THESIS AN TULUM AE CON ag HSA SED LS RAYMOND C. KINNEY oho P4 Cort EE eae ~~ - oF, ‘sa ~~ ~ “ wa . sy, c- ye . « ._ = a J NN . - . ee ~~ ; ; —_* Ee * f THESIS A A Commercial Lighting In Offices, Stores and Show windows A Report Subimtted to the Faculty of the Michigan Agricultural College Raymond C. Kinney A Candidate for the Degree of Bachelor of Science. June 1021. THESIS 401993 CONTENTS Preface----------- - 2-22 - + e+ - ee = 2-2 Bibliography----------------------------------------- IMTBODUCTION Fundamental Concepts Units OF Measure The Candle Mean Sph. Candle Power The Lumen Foot Candle Foot Candle Meter CHAPTER 1 The Story of Artifielal Light CHAPTER 2 COlor The Language of Color Effect of Color oh and Ceiling Meas. of Refl. Factor of Walls Color Chart Chapter 5 Good Lighting Practice Glare Eliminatio of Glare CHAPTER 4 Caleulation of the Lighting Installation Candle Power realtions Method of Using tables Flux of Light Method Utilization Constants Medified Flux of Light Method Examples Revising a Present Installation CHAPTER § Tests on Various Unite Phantom View of Comm « Unit Comperisen of Types of Units CRAPTER 6 Lighting of Office Buildings liethods Comparison of Systems Spacing of Outlets Wattage Required ¢ e 4 07 105 106 107 109 211 117 118 CONTENTS (Cont 'D) Lignting Corrédors 120 Misc. Uses of Light 122 Examples 125 Poair Graph of Duplexalite 127 Guplexalite Units and S hades 28 Hxamples 129 CHAPTER 7 Store Lighting : 133 Utilization of Light 133 Quantity of Light Required 133 Cause of Effect 134 Direct Lighting 134 Semi Ind. Lighting 157 Indirect ,ighting 139 Lighting biassware 139 Totally Bncl. Globes 140 Ceiling Outlets 141 Light and Advertisement 141 Dppartment and Larke Stofes 145 Stores ov Medium Size 149 Exclusive Stores 1§1 Small Stores 162 Yiuumin . Intensities 154 Coeff. OF UTILIzation 184 Calculation Of Required Wattage 156 Amount of Light Required 158 Classes of Installation 189 Comments 166 Examples 167 CHAPPER S How to Plan Window Lighting L171 Comparison of Illuminants 173 Brightmess of Window 173 Importance of Background 175 Reflectors and their use 176 Possibilities in Color Brfects 183 Spacing Rfelectors 187 Concealment of Tiluninants 188 Sign Transparencies 1.89 CHAPTER 9 Maintenance of Lighting Sgstem 1021 Depreciation of Lamps 192 " " * Reflectors 195 Surroundings 1398 CONTENTS (Cont'd) oystem of Cleantng Method of Cleaning TABLES NO. 1 Intensity on Horiz. Plame 8S Zumen output Of Masada Lamps S0Spacing Mounting Height 42 Spacing ceiling Height 13 Classification 14 Watts Per Sq git. (Semi Enel. Unit) ist" (Sotally Encl. ) 16 ” " " (8ndirect ) 17 " " " (Semi-End. ) 18 " " " (Duplexalite ) CURVES SYMBOLS 199 201 205 204 205 206 207 209 210 211 212 215 214 219 PREFACE In th’s thesis the author has attempted to compile under one cover all necessary information necessary to properly design the artificial illumina- tion for offices, sto-es and store windows, There are no books on the market to date which combine the theoretical with the commercial side of the designing. As far as possible the author has given concrete examples and illustrations of the different methods in use and their epplication. Although the greater part of this thesis is not original with the writer, he cannot help but feel that the time has been well spent, since a quick reference library on commbrecial lighting has been the result. The author is indebted to Frof. Foltz of the of the electrical department for his preliminary course on flluminatinpns, and for his his many timely sugges- tions as to available material. BIBLIOGRAPHY BULLETINS ITllum. Design Data Effect of Color on Walls Brascolite Lighting of Office Buildings Calculation of the Lighting inst. Numerous trade publications Transac. of EF. F. S. BOOKS Illuminating Eng. Prac. Tha Lighting Art MAGAZINES FE. Worid E. World E. Rev? Gen. Flec., Rev. Blec. Jl. ZH. World Elec. Rev. & West. Flec. Blec. Rev. & West. Flec. Bul. 41 W. E. Co. Bul. L. D. 102 G. E. Cat. No. 8 Bul. L. D. 108 G. FE. Bul. L. D. 117 G, E. Vol. IX No. 2. Vol. X No. 8 Tll. Eng. Soc. Luckiesh Vol. 52, No. 2. Vol 73, No. 7 Oct. 5, 1918. Mey 1918. June 1917 July 14, 1°17 May 12, 1917. Aug. 25, 1917. INTRODUCTION "Twas a light thet made Darkness itself appear A thing of comfort." Light is one of the dominating agencies in life and progress for it is important to our most important educative sense- vision. The possibilities extend into all those activities which make their appeal to human oonsciousness thru the door- way of tision. The importance of lighting is limited only by the bounds of human activities and its broadest sense, its importance extends even beyond them, for it is one of the most important in the scheme of creation. The activities of primi- tive man were practicall: bounded by sunrise and sunset, and darkness was feared as the abode of evil spirits and of lurk- ing dangers. Doudtless light was merely a by-product of the fire whose primary function was to furnish heat, nevertheless we may imagine primitive man with his burning kno® exultent in his victory over Nature. This achievement was one of the most important mile stones on the highway of human progress. Man's activities were no longer limited to daylight hours end greater opportunities were before hin. In the early days of lighting as a distinct profession, the engineering aspects were given prominence. In fact, lighting today is practiced largely from this standpoint not withstanding that the efficiency and adaptability of modern Llluminants have made possible the realization of lighting to meet very largely all the requirements of the human activities -_ fF and desires in respect to this agency. With this growing atten- tion to lighting we find as in many other activitics, that ag in-many other wetivittes; thet the deeper we delve the more extensive are the ramifications and comparitively smaller is the part of the apparent whole with which we are thoroughly familiar. For this reason arg the -hysiologist and ophthal- mologist have been attracted to the problems of lighting which involve the visual organs. The physicist ppecializes in many of the problems of production and utiligation of light. The psychologist finds an unexplored field for his endeavors for finally the problem of lighting is largely psychological. fhe artist finds an outlet for his ability in clothing scientific lighting principles with artistic exteriors in lighting fix- tures, also in using lighting as a decorative medium by "nainting” with licht as obtained primarily from the lighting units. As we delve deeper into the problem of lighting we find many intimate relations between lighting and the various sciences and arts all of which must be appreciated by the lighting practitioner before he is worthy of the title of lighting expert. The illuminating engineer should recognize that the esthe- tics sense however dormant, is possessed by all humen beings as is evidenced by the things about us. Perhaps we would not a-ply the term, artistic, to magy of the scenes that greet us during our daily routine; however, as we critically view any of these scenes and eliminate in our imagirea tion all that is not purely utilitarian, how different they would appeer. Imagine this done to everything on earth and a fair apprecia- tion of the value of the artistic and beautiful is obtained. On theother hand the artist should appreciate that in a broad sense in lighting, utility cannot be divorced from beauty. In fact it is misleading to use these two terms as if they had nothing in @mmmon. Beauty is in itself certainly useful as veiwed from the brodd outlook upon life. The philosophy of the deautiful teaches us that beauty is the harmonious en- semble of the various parts, hence in lighting figtures beauty in a broad sense is the harmony of scienoe and art. But the consideration of the artistic aspect of lighting should not end at the fixtures. In faot the greater figsld lies beyond them in the distribution of light on the various surfaces, such as walls and floor, and in the prduction of shadows appropriate to thes etting and in the color which best fits the spirit or mood of the occasion. This is one of the most neglected aspect of lighting altho it is one of the most extensive fields for development. Inasmuch as the prime object of the lighting specialist is to sefeguard vision he secks for rules which limit brightness and brightness-contrasts to safe values. Research is contributing much of value by direct attack on these problems. However, a rule which it seems safe to follow, is that if the lighting does not offend the finer esthetic sensibilities it is mot likely to be seriously hara- ful in its physiological effects. Such a rule cannot be app- lied safely as a criterion of the best possible illumination ~ but glaring lighting conditions have no place in an esthetic harmony of light, shade and color. In the industires and in various other activities in which the vision is taxed the problems of lighting are not solved by providing a sufficient intensity of illumination on the working planes. In each case the various specific activities should be studied in order to arraéug at the very best scondi- tions for seeing. Sometimes objects on which the eyes are focused are best seen as high lights on a dark ground and other cases as dark shades against a relatively brighter ground, The character of the shadows which is determined by the position and angular extent ot the light source and by the amount of scattered light reflected from the surroundings, is of importance in distinguishing objects. The color of the surroundings the spectral character of the illuminant and the environment as a whole are factors that should be considered and controlled by the lighting specialist in so far as he is able. What is Good Ligh‘ ing? fhe anawer to the above question depends upon the interpre- tation of the word "good", and this interpretation depends upon the viewpoint of the observer. An interior may be well lighted from the utilitarian viewpoint, with good uniformity and sufficient intensity and yet badly lighted from the artistic viewpoint. There is a great hisunderstanding regerd- ing what constitutes artistic lighting. Some believe that artistic lighting fixtures in the same ssale of mamificance as the interior decorations should be conaidered. In faot, t:i8 is the general impression of "ertistic lishting” and it has become so prevalent that those who are not skilled along this line have come to feel that, for the average atore or home, artistic lighting is an extravagance far beyond realization. This misunderstanding has arisen because no general information has been circulated resarding the true relation of esthetics to lighting. This relation is so {mportant that to neglect it is positively detracting from the complete value of lighting to the consumer, a detraotion which no eleetrical salesman should allow to exist in his community, and one which i8 is possible to avoid, providing a little consideration is given to the subleot. Every salesman who has to come in contact with the consumer realizes that the consumers’ satisfaction is the bigzest asset in the salesman’s and his company's favor. Satisfied customers do not complain, and become “boosters” instead of “knockers,” and every corporation needs as many friends az it can get. Satisfaction from lighting depends on something more than economy. The consumer who si continually subjected to the “eoonomy" argument is alway s anticipating, and demanding greater economy. And economy, like everything else, has its limit, although it is difficult to draw the dividing line in sich cases. For example, the proprietor of a drug store was dissatisfied with the lighting of the glass urns filled with colored solutions, suapended in his window, and requeated a b local electricrl salesman to suggest some method of improv- ing same. The salesman after a superficial study of the con- ditions recommended that larger Mazda lamps be used. In accordance with the usual method of lighting such urns the lemps were placed in sockets attached to flexible and adjust- able tubing so that they were placed directly behind each urn, constituting a misereble ineffective and inefficient arrange- ment, for the contents of the urn could only be effectively illuminated when the observer wes standing in one position-- Girectiy in front. The view from the side dis closed the lamp and the glare was so great that the whole effectiveness of the urn and its oolor was destroyed. In addition, the larger lamps increased the current consumption and at the end of the month the druggist became infuriated, upon receipt of a bill considerably in excess of his average amount. The salesman in his anxiety to satisfy his customer went from one extreme to énother and installed Mezda lamps of the smallest possible type, which failed utterly to reveal the coloring matter in the urns, leaving the druggist thoroughly dissatis- fied despite the reduction of his bill which ensued. By chance ea lighting expert in the employ of the lighting company was consulted and suggested that lamps of the originsl size be used in a new way. The novelty of his suggestion immediately eroused the interest of the druggist and 1t was carried out. The colore’ solutions were remcved from the slaas urns and their inner surface wae steined with ordinary lamp coloring. The lamp wes then pleced inside end the effect when lizhted ~~} was that of a uniformly colored turn, equally attractive from any viewpoint, either by night or ‘by day. The opal coloring which was used gave translucency without bprensparency and neither the lamp itself nor its filement could be seen through the colored glass. The dumgsist wes not only satisfied but enthusiastic and became a first-oless "pooster" for the com- pany, assisting their district representative on more than ene occasion to close a prospect. This is mm example of food lighting and good business combined, and where you find one \ . you will usually find the other. The Practical Side of| It. There is such a wide variety of Lighting equipment available to-day that there is positively no excise for not specifying the right thing. It is just es easy to give a customer what he needs, instead of what he thinks he needs, if you oan pre- sent the facts to him so he cm grasp them. Don't make the mistake of letting a man buy the wrong fixture because he thinks it's right, for eventually you will be blamed for the transaction. Be careful as to the size of a sixture with ref- erence to the interior or space it is to ocmpy. Nothing 1s more crude or inartistic than a massive fixture in a small interior or ceiling area, and a very small delicate fixture in a large room. After you havéd determined your watts per sQuare foot distribute them so that the effect to the eye will be harmonious and pleasing. Never specify lighting systems with direct a great deal of light upon a ceiling unless the ceiling is a good condition and will stand such exposure. Avoid gaudy ornamentation on glessware and fixtures. Those festoons, wreaths, and dedallions stamped out of cheap metal and soldered to cheap fixtures should be blacklisted. They are the stock in trade of the alley-way electrician and junk man. QObdtain some photographs showing examples of good taste in lighting for large and small stores and residences. Show these but don't make the cistake of copying exactly-- inject some originality tnto each particular case, and tell your pepsepect why he Should be determined to have something different. Remember that the efficienty of the Mazda lamp is so great that energy cost need not restrict you from planning and ocarry- ing out any lighting scheme which may decur to you, providing same is based upon the recognized prindiples of efficient direct indirect, or semi-indirect illumination. Don't expect to use the lamp é@nefficiently and obtain an artistic effect, tthat is where the principles cf illuminating engineering must be carefully observed. When inexpensive bowls are used, avoid "prassy" finishes (even brushed brass is becoming too common, ) amd other finishes can de obtained even in the cheapest kind of fixtures. Under conditions where blefiding or toning a fixture's metal work in with the celling is not possible you will get the best results from a bronze finish, which is le sting and does not depreciate so quickly from the effeots of dirt and general wear and tear. The idea of "matching a figture with the radiators and steam piping is a mistaken one from an esthetic viewpoint. Pipes and radiators are never objects of art, and their ugliness should be concealed by painting them (in a dead finish? to blend exactly with their background. Then they are unnoticeable. The same treatment applies to wall switch plates and panel boxes, lighting men seldom have the power to make stoh changes but they ought to know about them, and make sugges- tions whanever possible. Do not recommend silk shades which are so thin that the filament of the lamp shows throught If you are obliged to recommend such lamps, instruct thepurchaser how to cut a slit in the inside lining and introduce therin a filler of thin white paper (between the inner and outer lining) which will eliminate this defect. lu Fundamental Concepts + A mastery of the principles of illumination can ge grined only by studying the subject from the ground up. In this, as in other scientific subjects, it is necessary at the outset for us to familiarize ourselves with the various terms used in the art, especially those terms which designate units of measurement, for these terms constitute the foundrtion work upon which the final structthre is to be built. Just as we onoe had to learn that there is a unit called the yard which is used to measure length and t\at this unit has been subdivided into three feet and each of these in turn into twelve inches, that the gallon is a unit used to measure quantity and contains 251 cubic inches, so in illumination we have certain fundemental units to study before measurements can be made and before de- finite relations of cause and effect can be comprehended or expressed. Basic definitions have a very academic and some- times avery technical sonnd, although the units themselves, once their definitions have been assimilated, and not merely learned by rote, are comparatively simple. The @efinitions which appear from time to time in this bulletin need not, therefore, be committed to memory but should be thoroughly digested so that the reader will grasp the distinction between the different units end obtain a working knowledge of what each stends for and the quantity it represents. The school- # N. L. Wks of G. £. li boy may be able to define an acre wery accurately, but a farner may not even know hew many square feet there are in an acre and still heve a better conception of the extent of an acre; the one point they both must first appreciate is that the acre is a unit of area rather than oflength or volume. Very few electricians or électrical engineers could off-hand give a basic definition of the ampere, although they might all know that it is a measure of the rate of flow of electric current and have a praoticaé& conception of the maghitude of the unit. If illumination it is of more practical value to have a con- ception of the quantity of light represented by one lumen--to , ce e {, ds Cane ee \ Only a slender cone of light reeches the eye. | know that, for example, 75 of these units represent the quantity of light given off by a lO-watt lamp--than it is to be able to tell precisely what a lumen is. If the unit of length which we call amile were arbitrarily made shorter, the distance between New York and Chicago would still be the sam, or if the dey were divided into ten equal parts instead of 24 hours tie planets would not change their speed of trave) or rate of rotation. Obviously, it is of adv-ntage to standardize certain units so that relations of magnitude can be expressed and under- stood with precision, although the value we arbitrarily assign as a standard is of little pmportence except from this stand- point. Units of Measure The Candle A generation or two ago when new light sources began to supersede the cendle, it was sost natural that the illumina- ting power of these new sources should be expressed in terms of the candle familiger to all. It is probable that the very first comparisons of two light sources were made by setting up the two lemps in the line of vision and geuging them by means of the eye, the most natural direction in which to look at the sources being the horizontal. The eye is capable of measur- ing only a very slender cone of light at one tim; in fact; if the eye is an appreciable distance from the source, the cone of licsht coming from a light assumes a straignt line. While there are an infinite number of directions from which the eye might look at the source, the light-giving power in a horizontal direction was made the basis of oomparisons, and the streagbh of the light in this direction from a candle made according to certain definite specifications, was abbitrarily chosen as the unit of intensity and called a candle. The newer illuminants appearing on the soene were rated accorddng to their strength in t is same direction and were steted to Give so many candles, so that when we say a lamp gives 10 can- dles we really mean that its intensity or strength in a horizon- tal direction is equal to that of a group of ten standard can- dies. This rating of a lamp is made by means of an instrument called a photometer. a description of which will follow later. One essential point to remember in t is connection is thet the candle-power of a lamp represents the intensity in one direc- tion only. In practice it has been customary for years to rotate the lamp about a vertical axis while the candle-power was being deter: ined and the result was known as the mean or average horizontal candle-power, but even this determination gives an average value of the intensity in the horizontal directions only. It should be stated, however, that in compar- >? pe «- . . ” , “. were oe c . PMp tee eek - _— a . ” ~-ye me - - -. - Lone . en Oar eee , ee e ) 1 ° . wat ~ , . ’ oF Via pie wo . . = be . oe > The Candle-Power in the Direction of the Photometer is Not Changed by Partially Surrounding the light Source With a Non-Refleoting Surface. ing lamps on the basis of their horizontal candle-power, the light in directions other than the horizontal was not really ignored, for it was taken into consideration that mort eources of light then in use gave off their light in about the eame proportions in the different directions and that for this reason the candle-power in a single dttection furnished a cri- terion sufficiently accurate for the needs of the time. To carry our conception of candle-power a little further, let us asevume the conditons existing es the diagram above. In Case A we have on the left a» stendard candle end on the right a photometer pointed toward the candle. Prom what has elready been stated, it iroveious that when the photometer is balanced it will indicete an intensity of 1 candle. In Case B we have surrounded the candle with a ephere having a moderately large opehing. The inside of the sphere, we will say, has been painted a dead black so that none of the rays striking it are reflected but are absorbed and cease to be lisht--in other words, are thrown away as far as our experiment is conderned. In this case the photometer will still indicate ean intensity of one candle in spite of the fact that a great deel of light has been thrown away. In Case C, we have used a sphere with a much smaller opening and are therefore wasting still more of the light, but even in this case our photometer will indicrte an intensity of 1 candle. In fact, our reading wi!l be 1 can- dle regerdless of the size of the opening, that is, regardless of the quantity of light we allow to be emitted, provided the direct rays from the condle to the photometer are not obstruct- ed. The proverbial candle hidden under a bushel will still give an intensity of 1 cendle if there is a small hole in the bushel for a beam to escape, although as far ae its illuninat- ing value is concerned, it is still "hidden under a bushel”. This leads us to the important conclusion that the candle- power of source gives noindication of the total quantity of light emitted by that source. Cendle-power, we may sry, is A. Opening OR has Area of 1 square foot and emits 1 Lumen B. one Lumen fails on Surface OPGR analogous to a measurement of the depth of a pool of water at a certain point on its surface--a measurement which is use- ful for certain purposes but in itself gives no indication of the quantity of water in the nook. The firat fundsmental concept we have to deal with in illuminetion, then, is ceandle-power, which is the measure of etrength of a source to preduce illwninetion in a given direc- tion, and thepower in a horizont:1] direction of a crndle made according to certain specifications and burning under certain conditions has been arbitrarily chosen as the unit 6or mensur- ing this strength. The mean spherical candle-power os a lamp is simply the average of all the candle-powers in 811 directions about that lamp. Fig. 6--The Illumination on a Surface Varies Inversely as the Square of the Distance from the Source to the Surface. this same beam of light would have to cover four times the area of A; and, inasmuch as we cannot get something for noth- ing, we would find @hat the average intensity on B, 2 feet away, would be one-fourth as high as that on A, 1 foot away, or one- fourth of a @oot-candle.. In the same way, if B also is remov- ed and the same beam allowed to fall upon plane C, 8 feet away from the source, it will be spread over an area nine times as great as A, and ep 6h; at a distance of 5 feet we would have only one-twenty-fifth of a foot-candle. From this we deduce that the intensity of illumination falls off not in propor- tion to the distance, but in proportion to the square of the distance. This relation is commonly known as the inverse square Law. Important Relation Between Foot-Candle and Lumen. If we refer back to Fig. 3B we see that the surface OPQR is illuminated every point to an intensity of 1 foot-candle. We also know by definition that the quantity of light falling on the plane OPQR is 1 lumen. This gives us the important law that if 1 lumen is so utilized that all of the light is spread over a surface of 1 square foot, that surface will be lighted to an average intensit:: of 1 foot-candle. This rela- tion greatly simplifies the designing of a lighting installa- tion, for once the number of square feet to be lighted and the intensity of illumination which it is desired to provide are known, it is a simple matter to find how many lumens must fall on the working plane. If, for example, it is desired to il- luminate a surface of 100 square feet to an average intensity of & feot-candles, 500 lumens must be utilized. The designing of a lighting installation is taken up more in detail in succeeding pages. Foot-Candles Meter. An instrument calicd the foot-cendle meter has recently been designed to measure foot-candle intensities quickly and with a fair degree of accuracy. It is very simple in operation, so light that it oan be easily cerried about, and so small that readings can be taken in very restricted speces. The instrument is shown in Pig. 7. In operation, it is placed up- on or adjacent to the surfece on which a messurement of the foot-candle intensity is desired. rticularly advisable for wall tints where there is a large window exposure to the north and east light. It is a well known fact that the strong rays of light existing et certain seesons of theyear are very irritat- ing and injurious to the human eye, if they ere allowed to enter through a large window surface and strike the eye directly or indirdéotly from polished surfaces at certrin angles. If light tinted walls extended down to the floor line, employees, when looking up from their work, would be confronted with a ef. ZK. 8. 8S. Vol IX No. 2,1014. b4 bright wail surface which would to a certain extent, reflect too high an intensity of light and thus affect the visuel acuity or seeing efficiency of their eyes. With light green walls, the strong deylight rays are absorbed, diffused and re- duced in intensity, so that far more hygienic conditions are furnished the office worker. The same principle holds true with artifioiel Lllumination coming from overhead general i11l- uminetion. From a utiliterian standpoint, it is self apparent that a light green painted wall surfece is ersier to keep clean then one of a lighter color, when either a painted or celcimined finish is employed. Painted walls and ceilings, in preference to calcimined surfaces, are coming into use quite generally, because they are conceded to be preferable from both a sanitary and a utilitarian standpoint. Measurement of Reflected Facér. There are a number of laboratory metho’s of obtaining this value, some of which employ elaborate apparatus, and which take into account with a high degree of accuracy the direction of the incident light, color of incident light, and similar features. :st since the area of the oblique plane AC is obtained by dividing that of the normal Plane AB by cos a, the illumination of AC is that of AB multiplied by cos a, or for oblique illuminsetion, In= 608 Dosccccscccvcsecsccecserer (4) But from the triangle 08 A’ h So —- = COB Bececcccccsccesccesse (5) OF d SA h Ee cece ccc ce cn cece eccesccccesee (6) COS a h Squering, a? n_- cece cece ecco cecescvee(t) cos a Suystituting for a® in eqqation (4) In ne Cos” Becccccccccccsvscccescses (8) Where In is the intensity in foot-candles on the horizontal plane. Equation (8) is known es Lambert's law, and is very use- So ful in the calculation of illumination. In the reat of the bulletin on page 22 will be found values of cos” a for different values of "a" from 1 deg, to 90 dig. To facilitate the use of the above formula there are given in Tabhe No. 1 values of illuminrtion on horizontal planes at different heights and at different horizontal distances of a light souree of 1 candle-power and also the corresponding angles made by the light rays with the perpendicular to the plane, or angle "a". Method of Using Tabhe Odtain the distribution ourve of the lamp and reflector in use or to be used. Take from Table No. 1 the value [in foot-cendles) of flluminstion which a 1 crndle-power light source would produce at the point seleoted. Also note the engle corresponding to this point. From the distribution curve of the lamp, take the scandle-power at the correspond- igg angle. Multiply this velue by the illumination value found in the table, and the result will be the illumination, in foot-candles at the point selected, of the lamp under consideration. For example: Required the illumination produced by a 200- watt bowl enameled Mazda C lamp with RIM standard dome reflec- tor at a point 12 ft. below thelamp, and 12 ft. to one side. From Table No. 1, the value corresponding to these dis- tances is 0.0088, and the corresnondign angle is 45 deg. From the distribution curve of the 200-watt bowl enemeled Magda C lamp with RLM standard dome refilestor the candle- SS power at 45 deg. is approximately 475, then 0.025 x 475 equals 1.1878, which is the lllumimation 18 foot-pendles at the specified point. The illuminrtion on a certain spot where there is more than one lnmp in the firld of vision may be obtained in a similar manner, using the respective dis- tances, from the point directiy beneath the lemps to the spot and the vertical height of the lamps above the plane. Obtain values from Table No. 1 end proceed as above. The sum of the values thus obtained will be the total amount of Light on that specific point. Illumination of Vertical Surfaces, For formulee for the calculation of illumination on vertical eurfaces and surfaces at other engles than the normal or horizontal, see a paper by Mr. F. A. Benford , Jr., entitled "fhe Theory and Caleulation of Illuminating Curves," Trans- actions of Illumination Engineering Society, Volume 7, 1912. Flux of Laght Method (method No. 2) While the "point by point" method is fundamental and must be used in calculations involving equipment whose cheracter- istics are not fully determined, it will be found too ocumber- some for general use and a more convenient formala would ob necessity be essential. A lumen is a qurentity of light which will illuminate 1 squere foot of area to an intensity of 1 foot-candle. A table is here giving intensities in foot-candles recommended for the various classes of lighting service. The floor area So of any given room is readily ascertainable, and this multi- plied by the desired foot-candle intensity gives at once the lumens which should be effective on the working plane. From an inspection of the distribution curve of any lamp or of a lamp and reflector combination, it is apparent that all of the light flux (emitted lumens) from the lamp does not reach the working plane; for in the case of a bare lamp approximately one half of the total light is emitted upward, and to reach the working plane must strike the ceiling 6 end side walis and then be reflected. Since there is no perfect reflecting surface, any reflection is accompanied by abdsorp- tion and lose of light. This is true e-en in cases where re- flectors sare used, for a reflector, no matter what its re- flecting ecurface may be, has a certainportion of the light absorbed by it. This may be shown by comparing the light emitted by a bare lemp and the seme lamp equinped with a re- flector. An obvious method of determining this loss of light is to set up &n an average size room with certain colored walls and ceilings, an installation of one type of reflector; then to actually measure the illumination on a horizontal working plane, and also determine the total light supplied, or gener- ated lumens. Many such investigations have been made with various types of units from the direct steel refledtors to totally indirdct units, and utilization faetore thus de- terminédg may be found in Table No. 2. mhe values in this table represent the percentage of thé total lumens emitted by lamps thet reaches an assumed working plane. WHILE THE values of the constants civen in this table may appear to be a little low, theyrepresent average conditions of service Table No. 2. Utilization Constants - Per Cent Lumens Effective Allowing a 25 Per Cent Service Depreciation. Celling...srrcsccveseree Light Médium Dark Wall@.cccecrcscceese kt. Med. Dark Lt. Med. Dark Hed. Dark Reflector R.L.M. Standard Dome, Clear ....... .40 .47 .45 .48 .46 .44 .48 .44 RIM Stendard dome Bowl enameled........42 .41 .39 .41 #.40 #«F8 22 #=.38 Deep bowl, steel CleOarterccsccccccseseseh «oD 097 239 .88 1.37 58 .57 Reflecto Cap Diffuser Clearecccvecscccceesedd 0% of 4.34 655 = 66310 W528 SL Deep sowl, Glass Bowl enameled........40 .88 .56 .357 .385 .33 .32 «312 Dagfusing, onc. globe Clear.... S®ese0n0vee#e# @ eal 204 coe 2d eo eon end 209 Light opal, semi- ind. Clear....csce ev4 eel. ,28 .29 .26 1.25 21 «41 Dense opal, semi- ind. Clear @e79#2t 68 8 one on? 25 2a enn of 028 214 Totally indirect Clear.wcccccessecve e027 25 wero e820 118 1.16 12 210 “Bowl enameled lamp, not generally recommended with the deep bowl opaque reflectors on account of the pocketing of light and resultant low utilization. with surroundings and equipments as indicated, taking into consideration a depreciation in lamp and reflector equipment JL of 25 per cent due to normal dirt and dust collection. The results obtained from such testing, supplemented by calcula- tions, may be made use of in two ways. There are times when it is desirable to know the illumina- tion from an existing system and a portable photometer is not available. By the use of Table No. 2, the average foot-candles may be obtained in the following manner. The total lumens generated dy the lamps may be obtained from Table No. 6. Know- ing the type of fixtures and color of the walis and ceilings, a utilisation factor, appiicable to the special case, may be found from Table No. 2. The total generated lumens, mul- tiplied by this factor, will give the total lumens effective on the working plane. Again, the total effective lumens divided by the area of the floor in square feet will give the average foot candles. I2 this way, the flux of light method is applicable for use with existing installations. On the other hand, it is also possible to determine the size of lamp necessery in a proposed installation where it is desired to obtain a certain foot-candle intensity on the work. In this case, the area of the floor is multiplied by the foot-candles desired, which will give the total effective lu- mens necessary. Dividing this fugure by the utilization factor adaptable for the proposed installation, found in Table No. 2, will give a total emitted or generated lumens which must be furnished by all of the lamps. The lumens per lamp may then be found by dividing the total by the number of outlets, and then referring to Table No. 6, giving the total . a” fw lumens for any stenderd lamp, the necessery sizes of lamp may be selected. It is always advisable to use a lerger rather than a smaller lamp, if there is a smell difference in choice as a safety facoor. The spsecing and hanging heights of the units will be discussed at length in the following method. Modified Plus of Light Method (method No. 3) In order to facilitate the work of laying out an instal- lation by eliminating as many calculations as possible, a sys- tem of tables based upon the avove discussion, has been drawn up to show the relation of the watts per square foot of floor area to the foot-candles of illumination, for different reflector equirments and grades of colors of yvalls end ceil- ings. Accordingly the following is =» short end yet reagson- ably accurate method of desicning a generrl Lirchting instal- lation. Before attemtping to lay out a lighting installation, there are a few facts concerning the building or room which are essential. These are: Character of work to be carried on. Floor dimensions. Ceiling height (maximum hanging height) Distance between columns (if any) Color of walls and ceilings. In order to facilitate the gork, the first step should Jey be $o make a sketch to scale of the room under consideration. Having the information, before proceeding further ,it is necessary to determine the type of reflector which is to be used. Having determined the proper reflector for the special Glass of building, proceed tc Case 1 for direct lighting units, and to Case 2 for seni-indirect and totally indirect units. Case 1. For Direct Lighting Units. Waen an even illumination is desired over the entire working crea, there is a fixed relation between hanging height and apacing for the severel types of direct lighting fixtures. It is always ecviseble to hang the units as hizh as possible due first of all, to the fact that there will be more cross light and thus less dense shadows, and again, by increasing the heigit, the epacing is increased and a iess number of cutlets with the sore efficicnt larger sizes of lemps may be used. The celling heish:t cannot be taken as the maximun hang- ing height, however, as some space is taken up by reflector and fittings. Where it is possible to heng the units close to the ceiling, 1 foot clearsnce should be allowed. In other words, a ceiling 15 feet high would have a mazimum henging height of 14 feet. Again, if there is consideradle overhead horizontal belting which would osst objectionable shadows from lamps hung above it, the maximum hanging height is the heicht of the lowest horigontel belting. Ys To determine hanging height and spacing of units for the case uméer consideration proceed as folows: From table 10 showing the relation of the henging height of a unit to its spacing, determine the maximum distance be- tween units. Divide the widty of the room by the maximum spacing obtained above to determine the number of fows of outlets in the room. If this spacing does not divide into the width evenly, take the next larger whole nunber, wich will be the number of rows of outlets. In cease the roc is divided into bays by columns, as is usual in mill construction, consider each bay as a small serarate room. Divide thie number into the width of the room, finding the new sprcing, and thus determine the new henging heicht from Table 10. The dist«nee between outlets in each row should be approximately the seze as the distance jetween rows, and still have the length of the room evenly divided. Divide the length of the roomby the specing between rows determined above, and if this does not come out asa a whole number, take the rext larger whole number, which will be the number of outlets per row. Now locate the outlets on sketch so that the distence from wall to first lamps will be one half the distence between outlets (see Fig 2). We have now determined the spacing and hanging height of the units. It remains to decide upon the Ju size of the lamps to be used. Multiply distance between rows by distance between out- lets in rows to find the square feet area to be covered by each lamp. Refer to Intensity Table No. 13 for foot candles required for the partkcular class of work to be carried on. Find the equivalent watts per square foot from Talbes Nos. 14-18 for theparticular type of reflector to be used, and multiply this fugure by the area per outlet. The result will be the watts necessary per outlet. Salect the nearest sise of Kasda lamp, preferably the s size larger. Case 2. For Semi-indireot and Totally Indirect Units. A method of rrocedure similer to Gase 1 may be followed for these types of fixtures, using the values given in Tables 19 and 12. for spacing and hanging height instead of those of Curve No, l. Determine maximum speéing for e siven célling height from table No.1¢ and determine suspension length of fix:ure for fin- al sapecing from Talb@e 12. The size of lamp to be used is found in a manner similar to Case 1. Using the vrlues of watts per square foot for the desired foot-candles, found in tables 14 to 18. Revising a Present Instellation. Many times it is advisable or necessary to use the present out-lets in a building which is already wired for lighting, but where the new high intensity has not been in Ib use. In such cases, it is first necessary to determine the floor area of the building in square feet. Divide the area by the numberof ou‘ lets to obtain the average area to be taken care of by each lamp. Multiply this by the watts per square foot found in table 14 to 18. for the particular work and surrounding conditions. Seleet the nenreat size of lamp, preferably the one larger, which will be the necessary size to use. To determine the hanging height, knowing distence be- tweer. outlets use table 12. If this value ia much grerter than the raximum permissible, due to a low celiling, even 4llumination will not be obtained, and more outlets will be necessary. The room should be rewhred #nd celeulstions made as outlined in Cases 1 snd 2. 94 CHAPTER V TESTS IN VARIOUS TYPES OF UNITS Thies chapter deals with various arrangements and types of reflecting wnits installed in offices of the same size and finish, where the conditions for careful teating are especially feaovrable., The results of illumination tests are shown for the various systems on a basis of equal quantity of light flux generated and also in terms of the wattese which would be required to give an average intensity of 5& foot-candles. The character of the walls and ceiling surface is fully described and the results of surface brightness tests sre tabulated so as to indicate the contrasts which exist with various systems, and are given on a basis relative to white blotting paper and also in absolute vabues. Corridor lighting, loss of light due to dust collection and effect of room size on utilization factor are touched upon. The lamps used for tests were selected so as to give their rated csundle-pewer when cperated at the test voltage. The voltage for the test eireuite was reguiated by hand, thereby doing away with the necessity for voltage-eandle-power cor- rections. In the tests which will be direotly compared, the same lamps were used except where one test required clear lamps and the other bowl-frosted. The bowl-frosted lamps were rated before being frosted and the "clear' values used in computations. With the thought in mind that contrasts on the walls and ceiling are important factors in an illuminaticn design, sur- 28 face brightness readings wore taken at what arpeared to be the brightest and dimnest spots. These are siven in terms of equivalent foot-candles on white dlotting paper, for the rea- gon that it is a very simple and conveniont method and alse because the valnes so given furnish, it is believed, a better conception of the magnitudes than such wnits as ecandle-power per unit of area. fhe data would be incomplete without including velues showing the reflecting ability of the walls and ceiling. These reflection characteristics are given relative to white blotting paper, that is the ratio’ of brightness of the surface in question to that of white blotting paper in the same posi- tion and under constant and diffused light conditions. The various systems employed in these standard offices ere: (A) pour direct,opal glass units fitted with bewl- frosted tungsten-filament lamps. (B) Same as A except that reflectors are inverted and clear lamps used. (C) One semi-indiresct bowl with Glear lamps in central outlet. (D) One dndirect plaster bowl with clear lamps in central outlet. ‘B) Four mirrored glass indirect units with clear lamps. (F) pour direct prismatic glass, intensive, with bowl- frosted lamps. A single wnit of each system is shomm.in Fig. 7. marie System A is the cne gcnerally adoptod throughout the offices. The -thers are used in places where the require- nents are cpeoilal or where spocial consi ‘eration was givne te tne individual tastes of the occupant. In the tests A-F lamps of equal luminous output were used so that compariscns show the reeults obteineble with the different systems with the same amount of light generated at the lamps. It is hardly necesssry to state ‘nat the same wattage is not to be recommended; horever, it was thought best for purposes of comparison to make teste on this basis. Reflectors in ell cases were of the oorrect sise for the wat- tage of lamps used, except that in the mirrored glass re- flectors 1% was necessary touse an extension in order to in- sure the proper lamp position. A summery of the results of tests A-F, as outlined ebove, is given in Table s 1 and 2. Before comparing these systems with one another and with | the efficiensy figures in other installations, the exact con- ditions es regards spacing of outlets end character of walls an' ceiling surface should be borne in mind. The walls are finished with a greenish-grey paint which reflects 53 per cent ef much tungsten fllament light as does white blotting paper used in cll these tests showed on measurement by the Rutting# reflectometer method, a coefficient of reflection of 77 per cent. The walls, therefore, absorb 59 per cent. The *Tiluminating Engineering gociety Transrotions, Oct. 1912. alr ceilings refi: ‘6% 76 per cent. as compared with the blotting paper, and, therefore, absord 41 percent. of the light fali- ing upon then. fable I. - Intensity Distribution. Description Test Direct, 4 units opal glass, bowl frosted lamps A Semi-indirect, 4 units, opal glass clear lamps B Semi-indiresot, 1 unit, diffusing bowl, clear lamps C Indirest, 2 unit plaster bowl, Clear lamp..... D Indireot, 4 units, mirrored glass Glear lamps B Direct, 4 units prismatic, bowl- frosted lamps “°F Reom area--257.5 square feet and each test. Tilliumination Foot- candles on °O" plane Avera Maxie Mini- age mum 806 BU 4.68 §.54 3,8 2.69 5.91 2,32 3.10 §.6€8 1.78 2ece 3.66 1,42 2.65 ©el4 2.20 5.00 5.78 4.33 Brficiency Lumens Per Cent por Btili zation watt efficiency <.%5 02.8 1.70 19,9 2.05 22.6 1.54 17.0 1770 318.7 o.22 35.8 4--100-watt lamps used in Celling height, 11 ft. 10 in. Height of unit above floor, Tests A, Band F, 10 ft., & in.3 Test FE, © ft. 9 in. Tests C and D, S ft 6 in. Fable 2. - surface Brightness Distribution. “Surface brightness foot-candles equivalent to white blotting paper. Ceilings Mazi- Nini- Description Test num THU Direct, 4 units opal giase déwil-frosted iamps A §.23 0.663 Semi-ingieect, 4 units opal glass, cleer lamps “38 1.98a 2.8¢1b Semi-indirect, 1 unit, diffusing bowl, clear Indirect, 1 unit plaster bowl, clear lamps D 65.16 9.280d Indirect, 4 units, mirrored glass, clear lanps ¥ 60.8a 1,940b Direct, 4 mits, prismatic bowl-frosted lamps F 5.59a 09.995b Fable 3S. Walls Maxi- Wini- mum mum 6 0368 8462 2.13@ 0.477f 1.356 2.593f 1.32¢@ 0.2635f 2.528 9.461f 2.67@ o.782f Reflection coefficient, per scent Relative to white blotting paper as obtained by dright- Surface nese readings. White blotting paper Walls in standard offices Ceilings in standerd offices New faotory white paint, worst New factory white paing, best New white finish plaster 90 120 120 Absolute It 4s possible with the best white paint to obtain a coefficient of reflection as high as &5 per cent. Measurements on new white finished piaster surfaces showed coefrfieient of Urs refleetion aa high as 02 per sent. Therefore, with the very best possible conditions, as regards ceiling, the illwmina- tion of the indireet systems could be raised more than 650 per cent. The semi-indirect systems could, of course, be made to shew nearly as great an increase if the best possible ceiling surfaces were used. Table © is a summary of reflection data for all tests. The lighting of reoms of a character similar to those tested involves not only the illumination of the working plane, but many other considerations such as the lighting of the walls, the elimination of cense shadows on the desks, etc. Utilization efficiencies given apply strictly only to this one size room with the same character of walls and eeiling. fThey are not representative of what may be obtained with larger spaces, an example of which appears later in the paper. However the size of the room and the finish of walls and celling represent a fair average of office buildings in general. From Table 1 it may be seen that the four 19°0-watt direot prismatic units gave an average illumination of & foot eandles, which 46 hisher than for any ofhthe others. since the wattage in each test wes the same, the prismatic units gave also a higher efficiency. Teble 4 shows the wattaze which would have to be used to obtsin the same auantity of light on the 30-inch plane. The differences in the direct, semi-direct and indirect LU4 syatems of lighting would, of course, be decreased if the celling were of a high coefficient of reflection. Even though the coefficient of reflection of the cefling is only Sv per cent., it has been termed a good white celling by meny observers, and so perhans does not differ greatly from tne averace cellins used in semi-indirect and indirect systems. Table 4 Wattage necessary to produce an | intensity of 5 foot- Desoription. Test. cendiles. Direet, 4 units, onsl glass, bowl frosted lamps. A 1909 Semi-indiresct, 4 units, opal gless, clear lems. B 186 Semi-indirect, 1 unit, dif- fusing bowl, clear lamps C 157 Indirect, &@ unit, plaster bowl, clear 1 lanps,. D 209 Indirect, 4 units, mirrored glass, clear lanps E 180 Direct, 4 units, prismatic bdowl-frosted lamps F 100 fhe “duel ouy JO afeTS se ze -UTDTT@ puw uUOTSfA JO OUTT yOOLTp ouy WOU YUuSMBTT} duet ay} ST 3200U0)--TeOg JO Jigg JoMOT ALTP pus FSup JO UOTZBTNUMOIN BYUEASTY ‘YuUSIZS TIN us eMOp BuTzoeT Jou out youed 04 ‘TaOQG wory sAvl pezZoeT jeu ous pus duet ou4 wmouy sAvl plvadn Oud TTS SZ}uleg--Taog JO Jeg Zeddg *eusrtd BSuyysox 92 pakusdy Weyq 8yoorTpoezd pues sAew puvadn UY SOUOIeD “VULTT THJowsea TTB BSxoeudD *poeToeusus uTeToolod eV ° 19098 JO Opay--10}7900TJ9G *4yuN 944 JO {ated Aue JO Olen SseTZ 9} Buyaocmeu quourxfa uoTytsod szedoad oy4 0% duet ou3 Jo quemisnfpe Agee o7, saoTTy--dasuEH eTQayeul py "LOPLOY o.% UF SYOTINO OY YFnoLYy IFS pezysou-Joins [[w soATAp pus Buyuedo Tl wus sTyy sxeque Upe Loos jo fky4ueTg--exequl ITy °890ds 3ZUBTUQ Pus BSUTL HOSTQ ‘saopeus Buy yusresd ‘SUTTTOO oyy 0% plwadn JEIXTTS 0% BUBITT JO Zunome BUST ey yang szyyused -meyy seyngzsy -3TD ple suazzos ‘QUBTT jo safer pruadn au4 szouzen ‘“‘ssuTB TedoO Jo epey--d6H0gq FUT OCTIey ‘ITw peyesiuszadns JO 47X@ OU% JOJ WTA Bodin 84fT UT pepTAocud syoT3aNO ‘eos 94 AQ poyroddNns--ddSpTOH TVeyzoR "§ONOOS PUd OGBUqQ CUBT Oy BOLJ Cmvy~ suzy JO Yuou suyzy 8zZIITJOPD 19938T I SUL “fO BIUIDIIA *¥JOJION ANVdWOD ¥ SVWOHL ‘f ’s O8DI1y) “OD s0j;2aYfay Koy-xX JoUoHON wapsig Ourzy617 js0fwoy akq ay) Aq payourwn))7 hil Doses PM ie | se — Pitas pe - J i = > with the present low cost of light, a tinted ceiling is justified where essential to the decorative scheme of the room or where lighting o8 a certain color tone is desired. fhe lumincus-bowl type of indirect unit produces the same gen-ral character of illuminetion as thet produced by striatly indirect units, but the auxiliary bowl, being luminous, give s a direct component which assists slightly in illuminating vertical surfaces, and, in the opinion of many, adds to the decorative value of the installation. Semi-indirect units of dense or toned glass give an effect very similar to that given by liuminous-bdowl indirect units, but they transmit a higher percentage of the light, and are, under usual condition, slightly more efficient. With bowls of light density, she results approach more nearly those obtained from opal-giass enclosing units; contrary to what might be expected, however, the semi-indirect system is often more efficient due to the fact that less light ia abosrbed by the bowl, less light is emitted in angles near the horizontal, and more light is directed to and diffused from the ceiling at effective angles. It is possible to obtain either indirect or semi-indirect bowls in exclusive designs harmonizing with the decorations and conforming to the testes of the user; regerdless cf the design of the exterior, however, it is of the utmost import- enoe that the interior be a hard, smooth reflecting surface in order that good efficiency may be maintained. In an in- stalintion which rune into any considerable e xepnditure, popes 4t ie well worth while to secure the opinion of a competent architect or decorator before determining upon a definite exteriof design. Lighting units of the same general type as are used on the main floor are suitable for the upper floors of large stores; often a smaller size of the same design may be chosen. In some cases, a well designed direct-lighting system may meet the requirements satisfactorily. With open reflectors, powl-frosted lamps should always be installed and the units should be suspended at such a height that they will be, as nearly as possible, outside the range of ordinary vision. As previously stated, Mazda lamps of larger than 200 watts should not be used in open reflectors. Semi-enclosing units are available, however, which operate on much the same prin- ciple as an open reflector but which are provided with a dif- fusing glass bowl below the reflector which screens the lamp from view. With such units, any size of lamp may be used. Their efficienesy compares favorably with that of the prismatic % pe of enclosing unit. Onall floors, the fixtures should be located symmetrically with respect to the divisions or bays usually formed in the celling by the constructional features of the building, unless it is desired to arrange the lighting to enhance some architectural effect in light and shade, or color, in accordance with a skillful designer's well consider- ed plan. Stores of Medium Size The lighting requirements of stores of medium aize are cae pact itera 4° ae i a } nko es ens Sia ree ’ : me a : it 3 i jail! weenie t jut? wane at ' - tie same as these cited for large stores, except that a loo- ation amid less impressive surroundings may decrease the neéd for purely decorative features. In ti:is olass of store & semi-indirect asretem employing some form of inexpensive medium-density bowl will often fully meet the recuirements of a distinctive and economical installation. A well designed direet-lighting system, auch as micht be used @n the unper floors of large stores, is very frequently deened entirely satisfactory,--espoctally where a semi-enclosing unit, of which No. 1, Fig. 1, is a type, is used. Fxelusive Stores. Exclusive smell stores or shops, found principally in the larger cities, lend themeelves to an artistic trecstment which is impossible in larger areas. In many coses, the use of colored lmmps to provide lighting of a distinctive tone is highly desirable, while uniforiity of illumination is to be avoided rather than sought. The fixtures may well be of special design but care should be taken to avoid the very common error of allowing too brillisnt light sources within the range of vision. Modifications of semi-é@ndirect, indirect, and enclosing fixtures are used aimost entirely. A prismatic glass semi-indirect unit has been recently de- veloped which consists of two glass bowls between which may be placed flowered silk, oretonne, or other G6edorative fabric of any pattern desired. The prisms, which line theouter surface of the inner bowl where they are protected from dust, insure an efficient distribution of the light; the decorative - 6 ‘, LO) fabdrie may be changed at will. Small Stores in General. Effioetency is the first requirement of a lighting system for the usual small store. A high intensity is neces- serv for the convenience of customers and for advertising purposes, but the fixtures may be of very simple design. Con- sequently, direct lighting with open reflectors of the prise matic or dense-opal type, or with a good type of semi-enclos- igg unit, is, as a rule, most applicable sithough often the installation of en inexpensive semi-indirect or enclosing unit is preferable. cemi-enclosing units possess ang advantege over open reflect ors in t at they diffuse the light from the filament cvér a comperatively large area; hence they may be used with any sige of lamp, and in locations where open reflectors would sause annoying clare. They possess an advantage over opalenclosing units in that they distribute light in muoh the same yay 9s a Jerse opal open reflector and are therefore less derendont for their efficiency upon the finisn of the walls and ociling. A common mistake in sinall store lighting is the installae- tion of a single row of direct-lighting refiectoss along the center of the etore, whore at least two rows of small units should be used tc prevent the customer's shadow from interfering with hic examination of the wares, and to iilumin- ate the shelving or hich cesce slong the sidewalls. A — singie row of semi-indirect or enclosing unita is, however, usually antisfactory. An exception to the use of bowl- frosted lamps with oncn reflectors may be made in the case of small jewelry stores where b#illiant refleetions in gens and eut glass may be desirable; the units should, however, be placed well above the ususrl line of vision to avoid glare. Illumination Intensities. A lighting installation serves : couble purpese: first, it permits the merchandisc to be examined with comfort; second, it advertises the store. Light is recognized as one of the least expensive and most effective advertising nédiums and hence intensities higher than abdsolutely necessery for comfortable vision are almost universally demanded. The three f-etors which govern the selection of an intensity for any particular case are: the nature of the merchandise---for dark goods require a higher intensity than light gooda to a pear equally well illuminated’ the illuminaticn standerd of the immediate neighborhood; and, t ¢ amount which the owner feels is expedient to apportion fer the advertising value of a high intensity. The lower values of any tabdie of intensitiés should, therefore, be used cautiously and full weight given to local conditions. However, values aprilying to average conditions are useful as a basis upon rhich to estimate desirable intensities, and such values are civen in Table l. Coefficients of Utilization Intensities of illumination are commonly expressed in foo foot-candies and are not in themselves measures of the total quantity of light. To determine tne quantity of lisht re- quired te previde a given averege Liitensity, it is only necessary to multiply the earcrn in squere fest of the surface to be flluminated by the desired intensity in footecandles}3 the result will be tie quentity of licsht flux, or lurens, which must te supplied to the ares tc rroduce the desired feot-cendles inteneity. Obvicusly, if just sufficient wettace le inetelled tc aunnly the nurber of lémens so cale- culated the Jlluminetion will fell fer short of the desired value because of the light flux which wjJllbe ebeorbed by the reflector ecuippent end by the celling and verticel surfaces. The proportion of the light flux generated by the lempe which ie effective in illuminating the "working plene”, that is, an imaginary surface perallel to the floor and at a height of 2 1/2 to 2 feet above it depending upon the height of sounters, cesses, goods etc., depends upon the tyre of fixture selected, the color of the ceiling and walls, and the size of the room. Ceilings in stores are usually fairly light in color and @he walls are, in most cases, lined with shelves; hence, it is possible to give values for the propor- tion of light which is effective in illuminating the working plane for various reflector equipments for the different Classes of stores. These values, which are called coefficients of utilization, are given, as fractions of the total light of the bare lamps, in Tabie 2. 156 Calsulation of the Required Wattage In oaloulating the wattage required for a certain store the first atep is to decide, at least tentatively, upen the type of fixture, in accordance with the general principles discuesed above. The second step is to decide upon the in- tensity in foot-candles which will be needed on thwe working plane; Tavle 135 will be found helpful in determining this intensity. The t..ird step is to determine the lémens required to produce this intensity; this is calculated by multiplying the area of tine room in square feet by the intensity in foot- candles. Tne fourth step is to divide the calculated number of lumens by the coefficient of utilisation, expressed as a fraction; this fraction may be obtained from Table 2. The recult obtained will be the number of lumens which thex lamp must furnish to give the desired intensity. In order to take care of tne decrease from initial to average lignt output of the lamps, the number of lumens go calculated should be inersased by 19d per cent. A further number should be added to allow for depreciation due to the scollestion of dust upon tne lamps, reflectors, celiing, and walls. It is fo great imnortance that a schedule providing for regular and frequeng Gleaning be adopted, but even where units are cleaned thorough- ly once a ronth, 10 per cent additional lumens should be allowed for dust depreciation. The final value, then, re- presents the liwsene which the vere lamps should provide initial- ly. ues The lumens initially given by the Mazda lamps commonly used in store lighting are given in Table 6. With the total lusens known, the required number of lamps of any given wattage may be readily approximated by reference to Table 3%. Size of Lamp, Henging Height, and Spacing Distance. Of the lamps which will supply the required quantity of light, the sise to be chosen depends upon the ceiling height and upon the type of fixture, @.60., whether the fixture distributes the light over a large or a small area. Z@nclosing units and open reflectors should, as a rule, be suspended as high above the flcor as is consistent with good apperrance in order that the light sources may be as far removed as possibic from the renge of vision. This allowable hanging height determines the permissible spacing of units of any given type for reasonable uniformity of illumination. The maximum ratios 6f the spacin,; distance to the height of the unit above the working plane (not above the floor), which may be used with fair uniformity of flillumination with the various types of units discussed in toils bulletin, are given in Table lv. If greater spacing distances than tiose JIvctermined by tnese ratios seem desirabic, it should be remembered that as the spacing is increasec the degree of uniformity decreases rapidly. The greater the permissible spacing distance, the darger the lamps whioh may be used and the fever the nunber requirec. The fewor the units of a given type, the less the installation and operating expense, but the greater tre area affected by the failure of a lamp end the denser the shadows. 15s Gowever, if the ratios given in Table 10 are not exceeded, no trouble from t+ is source need be anticipated. It should be noted that conditions governing the hanging height and apacing distance for indirect and semi-indireot units are somewhat different sinse in installations of this type, the celling acta as the licht source. The hanging height may, in suoh installations, be chosef @rom considerations of con- venience snd appearance but it should be borne in mind that if units are hung close to te ceiling, the aress direotly ebove thr units will be brichtly lighted in contrast to “Antermediate areas; thie effect may be considered desirable or it may be considered undesirable, depending upon the effect which it fa desirecéd to produce. Shadows cast by the bowl of the unit and by the suspension rode or cheins may, if consid- ered objecticnable, be eliminated by dipping the lamps in an etechinz solution. The especing distence is debermined dy the helent of thse cellinz since the ceiling acts as the Light source. As previously mentioned, it may be Gealrable to obtain especial licht and shade effects in certain instances; where t..is is the case, the rules giver above ds not, of sourse, apply. Amount of Light Required. The first step in planning an installation {ia to deter- mine how much light will be required. The illuminstion te be supplies in any elven case will, of course, depend upon the purpose for which the light is used. An offices where people Poy are working continuously reavires relotively much more Light than en cuditorium. A store displaying derk colcred cerehane ‘ise reoulres a creater illumination then one dierleying lisht colored voods, for dirk coeds reflect te the eye only a very sreall proportion of the lfeht thet fells uron them. Again, beceuse of the neture of their business, sare stores require hisher intensities of Lllumincticen tren ethers of differert cherecter. A Seweler shevld heve brivhter lighting than a herdwere merehent. Then, too, the locetion cf the etore influences the degree to weich it shovld be lichted. In the brightly lic>tec downtown retail section, mere light 48 demended than in en cutlging or side-atreet business district. The fundementel requirements of satisfactory stors lighting installations ere: 1. Sufficient illuminetion of uniform intensity over the entire aree. 2, Freedom from glare, claring reflections, extreme contrasts in brightness, and troublesome shzdows. &, A system of good eprearance which is simple, reliable, ersy to maintain, end reasonable in operating cost. two Classes of Instellations In plannigs a commereial lighting inetalletion, one of the two following conditions is presentad: 1. Where the building hes not been wired previcusly, or where, if wired, the customer is willing to reorranga outlets, {if necesscry, to secure adequate illumination. Here the Wea; at greatest freedom is allowed in plaennigg the installation, which latitude permits t oroughly satisfactory lighting results. ©. Where no change or addition is to be made in existing outlets. In this case one has but to decide unon the proper type end size of unit to replace the present fixtures. The udvantage to be gained by changing over is then dependent entirely uoon the greater officiency end diffusion of light furrisned t” the newer units in comrerisen with less modern quipment,. The Planning or Jlluminabing for New Buildings of for Old Bulldirngss VWaere rxistins Outlets Need Kot be Utilized. e. Choose ti.c bype of lighting unit beat «depted te tne location, with due regerd to the several suggestions siven in tables. Db. Measure the ceiling neight of the room and decide upon the greatest praeticel mountings height of the lighting unite above the flocr consistent with the satisfactory appearance, For Encloaing and Semi-Enclosing Unita. In case the mounting may be close to the ceiling approximately ona foot must be allowed as the minirum mountable distarce tetreen the oeiling and the ocxter of the lamp fllement, as shorn. For Indirect Units. Ths cellirg is the principal listht source, hence the total distance from flcor to celling sivould be ccnsidered the mounting height. 6. Refer to the Spacing-Mounting Height Table, or the Spacing-Ceiling Height Table corresponding to the unit selec- ted, and find what the average distance between units should be that will correspond to the mounting height determined upon. The proper drop from the ceiling for Indirect and Semi- Indirect Fixtures is aiso shown in the table. @. Make a diagram to scale of the floor area of the room to be lighted and lay out on it the position of lamp outiets. If the width of the room is not much greater (fr.m 2 to & feet) then the spacing value just found, one row of outlets down the center will probably be sufficient, unless much work is performed near the walls. Otherwise, the outlets should be laid ou’ in two or more rows in the form of squares, or approximately so (see fig. 2) The distance between units being approximately the spacing distance found in c. ( see blue print ) at end of chapter Fig. 2. Showing how lighting outlets should be laid out to provide a practical degree of uniformity in light distribu- tion. Here each lighting unit is civen a definite area to illuminate,i.e., all the space falling within 7 feet from a point directly beneath the lighting unit. The distance between the outside row of units and walis should hot be greater than one-half the spacing distance (see fig.2). For office spaces it should be approximately =n Cc” « one-third the spacing distance. (The exception to this is in the case of general offices and other locations where it is essential to have a very good lighting clear out to the wails. Here two or more rows of wits are almost always necessary.) @. Compute the total floor area of the room by multi- plyihg its length in feet by ite width in feet (making due @llowance for irregularities in contour). f. Divide the area thus found by the number of outlets. This will give the average number of square feet which each unit must alluminate. &- Find from the Caassification Table, the class to which the lighting installation belongs. h. From the Table showing Watts per Square Foot corresponding to the type of fixture under consideration, select the column which most nearly describes t'e interior to be lighted. Tn this colum find the figure (watts per square foot) which applies to the Classification determined in g. multiply t::i8 value of watts per square foot by the area to be illuminated by each lamp. The result will indicate the size in watts of lamps to be used. i. The mounting height of units may be finally corrected for the actual spacing chosen under d. in accordance with Table. In other words, it is not necessary that totally and semi-enclosing units be placed right against the ceiling if the spacing permits a lower mounting height. Also, in the ease of units in the indirect class the drop from the ceiling abe should be corrected according to the spacing-Ceiling Height for the actual spacing distance chosen. Thus the problem is solved, as size of lamps type of fixnture, mounting height and spacing have been determined. For offices, stores, and other business places, a general system of illuminetion consisting of regularly spaced cutlets and units of uniform size is in almost every ease desirable. However, in auditoriums, churches, etc., sometimes more pleasing and decorative effeots can be ob- tained otherwise, although more often a uniform lighting system is used in such locations also. Case II--Planning an Installation Where Existing Outlets Must be Utilized. Here, in addition to choosing the type of fixture to be employed it is only necessary to decide upon the size of lamp and the mounting height of the units. Items b,o and d, as determined in Case I, need not here be cauculated. @. Compute the total floor area of the room to be light-~ ed by maltiplying the length in feet by the breadth in feet (making due allowance for irregularities in contour) f. Divide the area in square feet thus found by the number of outlets. This will give the average number of equare feet which each unit must illuminate. g. Find from classification Table No. 10 the class 66 which the lighting installation belongs. h. From the Table showing Watts per Square Foot corresponding to the type of fixtures under consideration, select the column which most nearly desgribes the interior to be lighted. In this colwan find the figure (watts per square foot), which applies to the classification (g). Multiply this value of watts per square foot by the area to be iliuminated by each lamp. The result will indicate the s size in watts of lamps to be used. i. It now only remains to determine the proper mounting height of the units. For enclosing and semi-enclosing units, when there is only one row of units, take the distance (A) between two units, See Fig. 3, of the width (B) of the room, 4f this value is larger than (A), find the best mounting height above floor gor this spacing. RPnelosing and Semi-Enclosing Units. If there is more than one row of units, determine the best mounting height, using the larger of the two spacing values, Aor A’ (see fig. 3). If, as is sometimes the case, the celling is not Quite high enough tp pespmit this mounting height, place the units as close to the ceiling as possible. But when the discrepancy between the mounting height indica- te@ by the Table , and the greatest height which the celling permits, is large, the number of outlets in the room is not sufficient to make possibile a lighting installation which will give uniform and sstisfactory light with any kind of lighting fixture. The customer should be urged to re-wire. For Indirect Units. For fixtures of the indirect class a check should be made from the Spacing-Ceiling Height Table II, to see if the ceiling is high enough to give aprroximately uniform illumina- tion with the distance which exists between outlets and alse to obtain @he proper drop from these units from the ceiling. If the spacing is found to be much too wide for the ceiling height the oustomer should be urged to re-wire. In ense the customer re-wires the lighting layout must be recalculated on the basis of figuring outlined under the Planning of Iliumina- tion for yew puildings or in Old puilldings where Existing Outlets Need Not be Utilized, Comments. Frequently it may be hard to decide between specifying one or two rows of lighting units,or the installation may so figure out that one is undecided as to whether, Gor exam- ple, 100 or 150-watt lamps whould be used. In such cases one must depend upon his best judgment and experience in arriving at the correct solution. In this connection it is well to keep in mind that in a store, absolutely uniform illumination is not necessary, and so the spacing ratios may be stretched a little where there is a considerable advantage to be gained by so doing. On the other hand, in an office, uniform illumination is a prime requirement, and when there is any doubt as to whether one row of units or two should be used always install two. Likewise, in deciding between two sizes of lamps, if it is felt that the location is one in which especially good lighting will not be s-preciated, one may be justified in choosing the smaller of the two. In the ed, however, the customer will usually be better satisfied with an ample intensity of light even though the first cost of installation and the current consumption may be a little hggher. Recommendations shold in nearly all cases be based on the highest lighting ‘ntensity classification as shown in Classification Tables. The better illumination which results is ensily worth the slight increase in initial cost and upkeep. rome cr e } Rzample Ro. 1. Lay out a lighting system for a newly built shoe store in the downtown distrist, requiring very good illwnination. Assume dark walisand ceilings and dimensions as follows: Length, 55"; width, 40's height, 16' a. The Ivanhoe Ace, a onespiece semi-e slosing unit, is chosen for this store. This unit is particularly suitable where the questionof maintenance is of considerable importance. B®. Sinee the ceiling height is 16° the greatest height at which the center of the fixture could be above the floor will be approximately 15'. However, in a room of these propor- tions a fixture suspended by 1 to 4 feet of chain would pre- sent a much better aprearance., We shell, therefore, set 13' as a tentetive mounting height. ¢. Referring to the Gpacing-Mounting Height Table, 10. we find that for a mounting height of 13’ the units should be 16'6" apart. ad. Pig. 4 shows how to diagram the room to seale and locate the outlets. It is evident that by dividing thelength of the room by the spacing distance (18'°6") we get the re- quired number of units lengthwise amd approximately 3 1/2. Oovicusly we should specify 4. Dividing the width of the store by the same spacing gives us arproximately 2 1/2 units. Bo we will have to put in three units across--12 units in all. This will mean a lengthwise spacing 1f 14° with 6'6" between end units and end walls, and a erosswise spacing of 14° with 6' between the two outer rows of units and the side walls. Lbs @e. Area of floor is 40x55x2200 sq. ft. £. Average number of sq. ft. each unit must illuminate is 2200 ¢¢ 12 or 185. 6. Turning to the Classification Table #135 we find that for very good lighting this shoe store requires an illumina- tion of 6 foot-cendles; that is, it falis in Class 6. h. Referring to Table 14, Watts per Square Foot for Semi-enclosing Units, it is found that a room witnr dark walls and ceiling having more than one row of units in class 6, requires 1.15 watts per square foot. 1.15 x 1835 = 210, which figure represents the wattage of the lamps to be used. Since Mazda C lamps are not made in the 210-watt size 200-watt lamps should be specified, enaus the problem is solved, and twelve 200-watt mazda C lamps in Ivanhoe Ace units should be installed, located as in Pig. 4. i. With our exact spacing (14 feet) determined we refer aghan to our Sproing-Mounting Height Table 10, and find that this spacing corresponds to a height of 11'6" above the floor. A length of chain which will bring the units approximately in this position will insure a good appearance and yoo@ illumination results. Should the sewner desire to economize on the number of outlets to the greatest possible extent it would of course be possible to place the units very close to the ceiling, thus securing a mounting height 0° 16'. From the Spacing-Mounting bY Height Table it will be seen that this height corresponds to @ spacing of 20', and under these condtions two rows of three units--8ix units in all--seuld setisfy the requirements. A study of the problem will show that 400-watt lamps should be used in this case. merase fe 2- Showing how sore ee hoe -O----%--loutlets should be laid out — at* to provide a practical degree Coie x _ fof uniformity in light dis- }tribution. Here each light- ing unit is given a definite | area to illuminate, i.e.,all the space falling within 7 -—jfeet from a point direotly beneath the lighting unit. a fond i ! eats LP ata eres : Pe een 2 Fig 3 = To the left is shown ; fr op the ground plan and an end ; elevation of a long narrow store, while Lower: down we have a store of the same length and height but of nh emma sbi 3 eo AC he Pe Oo Rd ct 2 narrow stores when one row i of outlets is sufficient, r the width of the store should | aes "i be taken as-the spacing fig- bre $e ure if it is greater than Babi the actual distance between a ; the outlets. When there are two or more rows of outlets 7 the ideal arrangement is b——« —| that of squares though rect- angles are satisfactory if the difference between the ~ length and breadth of the rectangle is not too marked. rd a Arrangement PY OLS co example eh Dy p Nee van) i Be > ; ene Cee hd - Lei . CHAPTER V2tt HOW TO PLAN WINDOW LIGE&TING The information contained in this thesis is the same sim- ple and complete ever compiled onshow window lighting. There is no superfluous technical data. The engineering of this important matter is boiled down and simplified so that mer- chants can quickly determine what is best for their particular windows. THB SHOW WINDOWS OF A MERCANTILE SSTABLISHMENT CAN BF MADE AS EFFECTIVE BY NIGHT AS BY DAY BY PROPER CONSIDERATION OF THE PRINCIPLES OF GOOD ILLUMINATION --- NEW EFFECTS POSé@ SIBLE BY SPECIAL CONTROL OF LIGHT DIRECTION AND COLOR The show window is an adjunct of recognized value in mer- chandising and should receive treatment in keeping with its commercial importance. » ae be soiree WB se SL ° = 3 = 38 Co fF = £5 3? 3 ze acs es s “_ 3a ge =. = & as 3 SG Serial Ne. 201, Description-Over _ s { Be | 7 Sa kj a: a L. WHITE COMPANY Columbus, Ohio Zz. y= ey ans S ness of the display near the window glass, this result can be obtained by combining the 18° reflector with the 30° and 45° reflectors in a ratio of 5 to l. X-Ray Reflectors Every window presents a distinct problem in lighting, and is treated as such with X-RAY reflectors. Those shown herein are the results of years of constant perfecting, experimental work and study, so that now we oen confidently present a reflector that meets any problem of window lighting. Clessification of Reflectors. For large rindows use the Jove or Jupiter with 100 Watt Mazda C lemps. For everage windows use the Scocp or Hood with 75 Watt Mazda C lamps. For very small windows use the Scoopette or Hoodette with 15 watt Mazda B lamps. Classification of Background Conditions. If the backsround permits people inside the store to seo the window lichting equipment use only Jupiter, Hood or Hoodette. If the equipment is not visible any of the reflec- tors may be used, fitting the proper style to the window under consideration. : Size Classification. For shallow windows use Jupiter, Hood or Hoodette, For average or deep windows use Jove, Scoop or Scoopette, These classifications will some time interfere. It is then necessary to decide which of the wrong conditions will Pra da BNA Brie) SG, oy Byes ae Si / . MMA hy) wes WY) iy Wile 7 least interfere with the production of perfect lighting, and sacrifice that one. Make note of the size, bvackground conditions and depth of your windows, check these against the above classifications and you will have no trouble in determining the proper reflec- tor. To secure perfect results you must use the lamp for which the reflector was designed and also the proper reflector holder. Spacing. In average installations the spacing, or distance from center to center for these reflectors, is about as follows: Jupiter-=- 100-Watt Masda C lamp........-.24 in. Jove -- 100-Watt Mazda C lamp..........24 in. Scoop - 76-Watt Mazda C LaAMpPwocccces seed in. Hood - 75-Watt Mazda C lamp.......2ee28 in. Poseibilities in Coler Fffects# Cclor is, of course, one of the show-window dresser's most effective tools, yet full advantage is seldom taken of the possibilities of artificial lighting in the renditionof colors. The color contrast in a display depends, among other things, upon the color quality of the light which is used. A favric is said to be red in daylight because it absorbs prac- tically all the other colors in the spectrum and reflects mainly the red. Under a green or a blue light, in which red rays are absent, the same fabore would appear almost black. Mazda lamps give all the colors of the spectrum, but their light contains relatively more of red and yellow rays than does day- *See chapter on color. light. Hence, these lamps emphasize the reds, yellows and browns, and likewise fail to bring out the blues and violets in their proper weight. By the cereful sel otion of color sc- reens, (see figure 1.) however, any color may be given emphasis. Thus for instance, if 1t is desirable to emphasize the whiteness of goods, on display or to bring cut the blurs in dressgoods *« color screen should be used which will absord a part of the excess red rnd yellow rays while freely permitting the others to pass. Blue-green glase of the proper selection will do this, but if correct color walue of ti:e light and a high efficicnoy are to be obtained a thorough knowledge of color must ve used in the sel ction. Lamps designated as Mazda C-2 lamps have been developed,whioh, through the effect of special coloring elemdénts mixed with the ingredients of the glass from which the bulbs are blown, give a light of afternoon sunlight quality at about the efficiency of the Mazda Blamp. The lamp manufaocutrer has placed the proper wWwuks color in the bulb instead of depending on auxiliary equipment, since other glass having the same anpearence as thet used in Magsda C-2 lamps might, bo the user's disedvantage, transmit light. of very different color value. Color variation is, perhaps, the most effeotive mecns of holding attention. A florist's window, for example, cen be made to change wonderfully by simrley changing the solor quality of the light which illuminates it. It it is lighted entirely by a white light, such as is obtained with Mazda C-2 lamps the whites, blues, greens and violets will appear to stand out because the reds, yellows and browns with which they are contrasted will be depressed. If the color qurlity of the light is made to change by adding tc the white light, brown and yellow lisht from amber-colored bulbs, the colors that first eppeerdd prominent will sppear to fade and the ysllows and browns will be given prominence. Again, if red light is addec to the white light, the effect will be to make the cons trasts between red and the other colors more marked. Such effects, cs mentioned, may be rea@ily secured by having aveileble in the window the colored lamns necessary. Tne chanzes from cne color to another may be made by a suite able flashing device and méy be sudden and contresting, or they mat be gradual and harmonious. The colors in rugs, dressgoods, wallpaper, pictures, reintings, etc., ere suscept- ible to the seme treatient. A window dresser who will make a etudy of the possibilities of colored li,ht as well as the possibilities of lisht direction will be nble to nroduce beautiful and unusual effects. The Intensity Necessary for Effective Lighting. The intensity required for show-window lighting depends largely on the brightness of the surroundings. Show windows located on "white ways” will require a greater intensity than those loceted on a der! side street. However, as light is one of the most inexpensive and effective means of advertising, an intensity higher than is absolutely necessaryfor suitable lighting can usually be employed to advantage. Another factor LSet Which must be considered in determining the intensity is the color of the display. An object is seen by the light which it reflects, and, therefore, dark-colored displays require more light than do those 6f Righter colors. Since the display of a show window is frequently changed doth in material and color, the flexible arrangement of lamp sockets suggested for securing directional lighting effects offers a method of vary- ing the intens ity at will. In general the intensities for window lighting range from 10 to 50 food-candles. The advantage of using reflecting equipment in show-win- dow lichting should be generally understood. When lamps are used without reflectors a greater part of the light falls on the walls, background and ceiling before it reaches the dis- play. Usually window backgrounds and ceilings are poor re- f'ectors and much of the light, which by the use of reflectors could be utilized, is lost. The mo t satisfacotyr reflectors for window lighting are the prismatic and the morrored glass. These reflectors afford good control of the light with a high efficiency. In lighting a show window the first question is usually one of how much light is needed. The statement that so many foot- candies are required is only of value when the equivalent is given in wattage. Many times the ammount of light required is expressed in watts per square foot of the window floor. While this designation is satisfacotry for windows in which the dis- play covers only the floor surface, it fails to do justice to to those many windows where the displays cover a considerable portion of the background as well as the floor. In other words, the floor space of a window is not the only consideration which enters into the determination of the wattage necessary to light a window properly. Simple Method of Caloulating the Lamp Fquipment. The following is a simple method of finding theintensity suitable for any show window re ardless of the display arrange- ment. This met':od is based on the efficiency of Mazda C lamps and of prismatic or mirrored-glass reflectors. For the purpose of calculatton show windows may be divided into ten olasses on the basis of intensity of illumination desired. Class 1 includes t ose windows in which the lowest standard of ill- umination will be permissible--an intensity, in fact, which would not be adequate in most cases. Class 2 includes the average country store, where a low intensity is sufficient. Classes 5 to 6 cover the average store; Classes 7 to & the de- partment stores of most cities. The finest windows of the largest stores end exclusive shops located on brightly lightcd streets fall in Class 9 or 10, representing the highest inten- sities which can be used to direct advantage. The first step in the calculation is to place the specified window in one of the ten classes. The next step is to add the Gepth of the window, in feet, to the height of the lamps above the window floor, in feet, and multiply this sum by the elass number of the window. The result will give the required watts per running foot of window frontage, assuming that 100-watt Mazda C lamps are to be used. To get the number of lamps neeessary the number of watts per running foot of window frontage should, of course, be multiplied by the window front- age in feet, and this result divided by 100. Should the window be other than rectangular in shape the length of the window f frontage whould be taken as the averace of the length of the actual window front and the length of the window background. This met od of calculation as described applies only where windows are to be lighted by a dirdot system using well de- signed mirrored glass or prismatic reflectors placed at the top of the window. Where Mazda C-2 lamps are to be used, since the 150-watt C-2 lamp cives approximately the same inten- sity as that of the 100-watt Mazda C lamp, due to the absorp- tion of light by the colored bulb, the number of units to be used is the same in either case. Location of Spacing of Reflectors. The spacing of reflectors varies from distances of 12 inches between centers (minimum) to 24 inches between centers (maximim). It would be absurd to define any set rules regard- ing the number of reflectors per window, eince every merchant has decided ideas regarding the brightness of his own window and insists upon carrying them out. Reflectors should be placed as close to the front of the window as possible to give best results. If a window is open on two sides, and it is necessary to illuminate the rear of a display, this can be accomplished by a second line of lights carried around th the side and equipped with reflectors of the proper type. mm certain lines of business the color of the display varies greatly, being either white or very dark. The dark dis- play requires much more light to bring out the quality of the merchandise. For t is reason it is desirable to have two sep- arate circuits, one 6or displays which are light in color and both for dark displays. Suggestions for this sort are greatly appreciated by users of electric light. Concealment of I) luminants. In order to give a finished appearance to a window, the illuminants should be concealed behind a strip of valance which may be formed of silk, paper, or paint upon the back of the window glass. The exposure of lights in a display window distracts the attention of the observer from the displey and is therefore undesirable. Another objection is the glare caused by exposed lamps which make it impossible for anyone to see the display clearly. The concealing strip can be placed directly below the transom bar in windows of medium height and, if the ceiling extends above this, the units can be placed upon a rack attached to the bar which is also coneealed by the valance. By lowering the lights in t:.18 wey and bringing them nearer to the display additional brightness is obtained. Moreover, in any high windows, the blank space above the mer- chandise is of no advertising value and, if brightly lighted, distracts attention from the trim. Such concealment of lighting, when well done, gives decided charsoter to a display window. MNO Sign Trensparencies. Tremslucent signs, painted on the back of the window glass at the top of display windows, require illuminetion, but it is westeful aml extravagent to employ translucent reflectors for this purpose. While the light which they emit in an upward direction accomplishes the effect, a considerable quantity is wasted in illumineting the ceiling. Such transparencies can be illuminated in a far more economical and attractive manner — vy placing behind them boxes containing small 15 watt Mazda lamps in aluminum reflectors, arranged so that their light is directed against the white inner surface (back) of the enclos- ing box, which diffuses the light, bhereby illuminating the sign perfectly without the characteristic "spotty" effect resulting from placing lamps directly behind sign letters. Incident Considerations. Whenever possible the polished surface of sabinet work within a window should be depolished, since it acts as a mirror in reflecting the images of the lamps and reflectors, causing a streak of light which detracts from the finished effect of a window and distracts attention from the display. To facilitate comparisons in window lighting a temporary strip of moulding, wired end fitted with lrmps, sockets, and reflectors, can be prepared and instelled in any window wi th- out disturbing the display. In this way one window may be com- pared with another and it is possible to immediately see any improvement which esists. This method is very effective in demonstrating the superiority of Mazda lemps over gas lamps and incandescent lamps of the carbon filament type. It also serves to show the greater efficiency and better light of the 100-watt Mazda C lamp compared with the 100-watt Mazda B lamp. Actual comparisons are always most convincing and “seeing is believing." CHAPTER IX MAINFFNANCR OF THE LICUTING SYSTEM * The proper maintenance of the lighting equipment is a very inportant factor in Lllumineticn. The housewife, for cxample, realizes that the home would soon become e very poor piace in which to dwell unless she msde periodic house cleane- ings ané attermed to the household duties in this respedat from day to day. T'.¢ industrisl plant, or office, would soon be- come unsenitary unless sorup people were employed. Qn the other hand, lighting equipment is often neglected from the time it 4s installed until it becomes obsclete. Fersons seem {2 believe that after onoe henging a fixture and screwing a lamp into « sccket no further attention needs to be given to this part of the home of office. A widespread campaign of educating the public in this respect is most essential and it is up to everyone interested in lighting to preach thk gospel of proper maintenance. The eleatrical contractor, ynen he has finished an installation of lighting, should not ieuve the job without advising the customer as to the necessity of cleaning. To quote a prominent officiel of the Department of Labor of an important industrial state, when addressing the annual convention of eleotric contractors, and dealers: * If you sell a man a motor, you usurlly give him an instruction ecard telling him how to ofl the motor, adjust the brushes, and the like. If y:u did Bbhe dem this and he did not %= TdT 7 7 On a ® Je -/ e@ ye oh! ~' @ ° ue a attend to the matter tirousn his own appreciation of the sub- jeot, the motor would sccr stall, turn out, and you would be justiy blamed. on the ether hand, many a lighting installation is sold sith no instructions or suscestions as to its maine tenance. "A ilgnting system demands careful maintenance. If it does net receive it, the intersity will scon drop so low that the men cannot see to perform their work. Ycu will get the blame. You will ve told that tre installation you dealigned anc installed is not adequate for the purpose. Your engineer- ing judgment will be criticized." Depreciation of Lamps. Inherent: As the Mazda larp is burned small particles of tungsten are evaporated from the filament and coltect on the lamp bulb in the form cf a dark deposit. with the Magda “C* lamp the gas current carries these particles to the upper part of the bulb, where they have lese effect in absorbing light than when deposited directly opposite the filament. Never- theless, any accumulation on the interior surfece cf the bulb ebsorbs light, and blackened lamps should, of course, be re- placed. It is comparatively simple to figure out the most economic point at which to remove lamps from the sokket, taking into account the price of lamps and the cost of current. For average conditions, when the candle-power has depreciated to between 75 and 89 per cent of initial rating the lamp should ve discarded. Of course, a photometric test might be desired to determine exactly the percentage of depreciation, but 190 ebservation and experience will soon indicate to tre Maintene ance Depsrtrent when a lamp has depreciated to approximately this velue. The Mazda lamp is designed to maintain ite cendle-power ebove the linits mentioned above for an average 1ife of 1000 hours’ burning, and at the end of this period | shouk@ be removed and discarded if the moat economic conditions are te prevail. Acquired: Not only does a black deposit occur on the inside of the lamp bulb, but dust coll: ets on the cuter surfece; flying particles of o11, or similar materials, are also de- posited here. Thie accumulaticn cuts down the light from the lemp and should te removed at the time reflectors are Cleaned. This is often more serious than realized. A ® @ concrete case, we mizht quote a test om some lamps which were installed in a grinding room, where the air was moist, and laden with stcel dust particles. talf of the lamps instalied for the test were removed st the end of a week and thr weneincor at the end of three weeks. The lamps vere taken toe the photometric lcoberatory end tasted. Those with a. weck's accumuleticn of dire showed en average absorption ef 16 por cent. Those removed et the end of three woens nad an everage ebsronption of 22 por cent. This cces not take intc account the loes of lignt which would Gcoeu due to the grease and dirt on the reflector. Putting this in other words, at ins end of a weit an increase over 15 per cent in Wattage, and at the end cf tiree vecks nearly 2c per cent increase in wattage, would be required in order to obtain the same illumination as secured when the lamps were clean. Of course, many conéitions are not as severe as this, and some-- for example, the foundry or large shop--are even more severe. Another important point, in regard to the lamp, is the question of having lamps of the proper voltage in use. While initially the installation may be correct as to voltage, on replacing or ordering additional lamps, an error may be made in specifying the voltage of these lamps. Mazda lamps are designed to operate at the voltage indicated on the label. This voltage rating takes into account renewal and energy costs. If the circuit voltage is appreciably higher than the label voltage, short life of lamps will result. If the voltage at the socket is considerably lower than that indicated on the lebel of the lamp in use it will not emit the peoper quantity = of light. To make up for this loss of illumination, it would be necessary to install additional lamps. yor instancéd, seven Mazda lamps operating at rated efficiency will give the equivalent amount of light of eight Mazda lamps operating 4 volts below the rated efficiency of the lamps. Before ordering lamps it is desirable to determine what average voltage is actually attained at the socket. where the volt- age of the system fluctuates during the day, or where it varies in different parts of the installat'on, it is proper to order lamps as near the average of this variation as possible. 1 oe 195 Depreciation of Reflecting Equipment. All Bamps and reflectors should be regularly washed and Cleaned. Thezx period between cleanings will vary with locality and type of equipment. Obviously, a stedél direct lighting reflector will not depreciate as rapidly as an indirect unit. In the case of the former the under surface of the reflector offers very little opportunity for dust to gather, and that on the lamp bulb will be the rpimary cause of loss. In the case of the inverted unit, however, a thin layer of dust soon settles on the entire reflecting surface,as well as on the lamp, which will reduce the light output appreciably in a very short time. Not only is this ture, but the very arrange- mont of parts makes the accumulation greater. With the direot lighting equipment, the reflector itself shields the lamp from falling particles, while they enter directly into the inverted unit. Table No. l. Approximate Loss in percentage of initial illumination on Working Plane. Weeks... 4 8 18 18 20 RIM standard dome...; § 8 10 12 14 Dense opal bowl direct Lighting. .ccveccsescers 7 10 15 16 19 Prismatic bowl direct LICHt~INg. -ecccccsccccs 9 13 16 19 22 Li~ht density opal vowl direct lighting... 12 18 24 28 30 Semi-indirect. ®@eeee8e@ee 14 22 29 58 40 Totally indirect..cece. 20 29 S7 44 §0 —_—r aes ee Se ate a 5 weet ee ee ee ee er ee ee ee oem. Cee 8 we ore na ew ewe wee Ons cu ee en 2 0 ee Se ae owe —- —— ew - _ -e — © ew e-em ee — =o me oe fae fees qs +4 < re 1 : . ~« . ‘ - - - , ‘ , 1 2 oe a —_— * - = 5 -~-- -@$@- -m2 «a= eee eee ¥ . 1 ' . ‘ . us - . ‘ . 1 “ ‘ » ‘ ~ - — - * - 4 “+e - - ws - - - -- ' = Y sam ” . . - we ee ewe ee _- - - { . ~~ L . - .« ‘ ce em ~ ' , a * e _ - i ' ’ \ ‘ ‘ - -- -- =e eo -- -- . = 1 4 { \ ‘ - 4 Table No. 1 presents figures on the approximate loss of iight for various lighting systems, based on average office conditions in an inudstrial city. For s me other locality other figures will apply. The country town will have less depreciation than the busy city. The figures presented, however, are fairly typical of average conditions. It can be seen that the steel reflector depreciates least, while the opal reflectors for direct lighting vary as to the density of the reflector. This is to be expected, considering that, with a ligt density unit, more light is transmitted through the glassware, and dirt on the outer surface will have appreicably more effect. Another feature enters in comparing direct and indirect systems. with direct lighting, the dirt gathers on the exterior surface and is readily visible to the occupants of the room. with the semi-indirect and totally indirect systems, the dirt gethers on the inner or reflecting surfaces and is not noticed until conditions become so aggravated that the illumination drops far below that intensity for which it was designed. Hence, a more careful maintenance of any ind:rect system ia exteemely important. Depreciation of Surroundings. As pointed out in another bulletin, the questionof color of walls and ceilings is very important. No matter how carefully painted a room may be, soot, smoke and other Loy agencies soon darken the surfaces of the room and cause it te lose considerable of its refleeting power. Any porous paint, suches calcimine or whitewash, is pergticularly suscept- idle to this effeet. In industrial localities it is fre- quentiy necessary, if maximum economy of iighting is to be obtained, to paint the ceilings every year and a half and sidewalls every three years. A test, to determine the reflection coefficient of the ceiling and walls at frequent intervals, may save considerable on the lighting bill. In general, paint is far eheaper than electrical energy, and in dirty piants painting or cleaning is especially important. System of Cleaning. Haphasard cleaning has not usually been found satisfactory, since the accumulationis so gradual that it is not readily noticed by those responsible. Much better success has been secured by organized cleaning, at stated intervals, under the charge of a maintenance department where one person is absolutely responsible for this. As pojnted out before, the periods between cleaning will vary with the locality and with the equipment. Considering average conditions and typical equipment, the fixtures in an office should be wiped out at least once every month, and removed for careful wash- ing emce every three or four mont s. In the foundry it is probably necessary to carefully clean fixtures once each week. The cost of cleaning again varies with the type of equipment and lator charges. As typical figures Gor indus- trial plants with direct lighting reflectors, from 3 to 5 cebhss UU for cleaning might be considered as average. Some figures o ovtained in a large office building where semi-indirect units of a fairly simple design are inuse, indicate that the cost for cleaning by wiping lamps and reflectors with a damp cloth and then drying is approximately 5 cents per unit. Removing the semi-indireot bowl from the fixture and carefully weshing costs approximately 10 cents. The most economic perio€ for cleaning a given installation can be obtained by taking into consideration the cost of power, the burning hours per day, the loss of light due to the accumulation of dirt, and the cost per cleaning. The caloulation is not involved, as indi- cated by the following exampéaéa. Using figures of light depreciation as given in Table No. 1, costs of cleaning, as quoted above for semi-indirect units, and a power eost of 5 cents per Kwehr., average burning hours per day assumed as 6, and 2)0-watt lamps in use. For a l2-week peridd, the following caloulatéons apply: total kwehr. consumed= 6 hours x 6 days x32 woeks x 200 wattts v9 = 86.4 kwe-hr. Case A, Fixtures wiped every 2 weeks, washed every 12 weeks. Cost of cleaning, 5%+5+5+5+5 ¢ 10 = 35/7 Equivalent power loss, 4% (from curve) or 86.4 x .04 = 3.45 kw-hr. Cost of loss energy, 3.46 x .05 = $.173 Case B. Fixtures wiped every 5 weeks, washed every 12 weeks. Cost of cleaning, 5 +5 + 5 410 = 25¢ Equivalent power loss, 5.5% 0 986.4 x .055 = 4.75 kwehr. 204 Cost of energy &e 4.75 x .05 = $.24 Case C. Fixtures wiped every 4 weeks, washed every 12 weeks. Cost of cleaning, 5 + & # 10 = 20¢ Equivalent power loss, 7% or 86.4 x .07 = 6.05 kw-hr. Cost of lost energy, 6.05 x .05 = $.30 Case D. Fixtures wiped every 6 weeks, washed every 12 weeks. Cost of cleaning, 5 + 10 = 15¢ Equivalent power loss, 9% or 86.4 x .09 = 7.8 kw-hr. Cost oflost energy, $.8 x .05 = $.39 —— Case BE. Fixtures washed every 12 weeks. Cost of cleaning, 10¢ Equivalent power loss, 14 1/2% or 86.2 x .145 = 12.5 kw-hr. Cost of lost energy, 12.5 x .05 = $.625 Method of clesning. For dry diré, wiping with a dry sloth or brush, then with a damp cloth, and finally drying all surfaces, will prove satisfactory. Greasy or wet accumulations en any type of reflector must be removed by washing. Seap and water are goed agents, but care must be taken to remo e the film of seap by rinsing thoroughly as dried soap accumulates dust very rapidly. There are a number of cleaners on the market, but before these are used on a polished surface care should be taken to see that they are soshoth as not to make microscopic scratches on the glass, and should not leave a film of clean- ing material. Most of these may be applied with a piece of cotton waste of soft cloth and polished off with dry waste or c’oth. Where lamps are hung high, and it is necessary to use a ladder to reach them, it is advisable to have on hand an extra gloye, or reflector, which may be put in place of the dirty globe, and the latter carried to the cleaning place. After washing, the clean globe can be substituted for the next dirty one, and so on. This procedure necessitates only one trip up the ladder for each globe or reflector. 2U0 Table No. 1. Showing the Intensity of Illumination in Foot-Candles on Horizontal site Plane at various distanced from a Light source of 1 Candle- &3 Power. od Table 6 # £=Lumen Output of Mazda Lamps. Subject to change Without Notice Size of 110-125 Volt 220-250 Volt Lamp Standard Lighting Service | in Mazda C Mazda B Daylight Mazde C Mazda B Watts Mazda Lumen Output 10. 76 15 125 25 226 191 490 o72 50 450% 480 442 60 575 75 6865 600 100 1260 875 995 945 159 2049 14290 200 51299 200 ZOOL 3900 4849 3.60 41900 §00 8750 5600 7850 750 15900 1090 19300 17500 *White Mazda Gu TABBE J # Spacing-Mounting Height Table for Semi-Enclosing and Total Enclosing Units. Stores Offices Mounting Permissible Permissible Permissible Permissible Height of Distance Distance Distance Distance Unit above Between Between Between Between Floor Outlets Outlets Outlets Outlets and and Side Walls Side Walls 9! ~ io? §' 10° 3! 9'e" 11° 5'6" 10 '6* 3'6" 10° 11 °6" 6! 11! 3'6" 10 '6" 12°6" 6'6" 12° 4! 11' 13 '6" yt 13° 4! 11 ‘'e" 14! 7! 13 '6" 4'e" 12! 18! 7'e" 14° 4%e" 13! 16 '6" 8 6" 16' 5! 14! 18'e" g ten 17! 5'e" 18° 20' 10! 19° 6! 16! 21'6" 11° 20° 6'e" 17° 23 '6" 12° 22' 7° 1s! 25' 12°'6" 23! 7'e" 19° 26 '6" 13 '6" 25' gS! 20° 28'6" 14'6" 26' 8'g" *W. EF. Bulletin 200 TABLE 12. Spacing-Ceilling Height Table For Indirect Semi- Indirect and Duplexalite Units. Stores Offices Ceiling Permissible Permissible Permissible Permiss- Drop Height Distance Distance Distance ible from Between Between Between Distanoe ceil- Outlets Outlets Outlets Between ing and and to top Side walls Side wallef Unit Q! 9°" 6! 9'6" 4' 16" 9°66" 10'6" 5 '6" 10 'g" 4'6" 19° 10! 11' 5'6" 13° 4's" 29" o'e" = 12! 6° 12" g' 21° 11! 12'6" 6'6" Lee" 6' 22° 11'6" 13'6" 7" 13 '6" 5'6" 23" 12¢ 14! 7° 14! 5'6" 25" 13 = s-18"6" 8! 15'6" e'e" 26" 14° 17° 6'6" 17° 7% SO" 15! iste" 9 '6" 18°68" 7*e" = 32" 16! 20! 10! 20! gt 35" 17" 22" 11° 22" s'6" 39" 18! 23° 11'6" 23! Q' 45" 19! 26' 12%" 25' 1a! as" 20! 26" 13! 26! 10'6" 64" “W. E. Bulletin. TABLE 13% Ciassification Table Stores and Other Commercial Buiidings Classified on the basis of Lighting Requirements. Department Stores and Large Specialty Stores Main Floors and Basement Other Floors Stores of Medium Size Book and Stationery Clothing Drug Dry Goods Furniture Grocery Exclusine Small Stores Light Goods Dark Goods Small Stores in General Cigar Clothing Confectionery Decorator Drug Dry Goods Florist Furrier Grocery Haberdashery Hardware Hat Jowelry Leather Keat Millinery “W. E. Bulletin. Average Lighting Class (foot candles) AAA PAOHMATAHARAAA AAA Off BHhhARA HM Very Good Lighting Class (foot candles) ~ vos RoaVrevDna Oo - DOADNADMMMOADMDDWGOAASBAD Claseification Table (Continued) Stores and Other Commercial Buildin s Classifieg on the Basos if Lighting fF quirements Small Stores in General (con't) Music Notion Piano Shoe Tailor Tobacco General Avditorium, Churoh Automobile Showroom Bank Barber Shop Dance Hall Depot--waiting room Drafting Room Bétel Lobby Dining Room Library Reading Room Lunch Room Office Restaurent School, Class and Study Rooms. Average Li ghting Class (Foot Candles) mm f mh hh Omnand & WD 2 hm OR sv lw t~ > _ Ss Very Good Lighting (Foot Candles) QADMDRAAAGA pas m= vVrA OOD & peo Or OAD TABLE 14 # Zable of Watts per Square Foot for Stores, Offices etc., When illuminated vith Semi-Snclosing Units and Clear Mazda C Lamps. sClass of One Row of Unite Tllumination as Expressed in Light Wallis Dark Waile Lizht Wells Dark Walls Foot Candles. and Ceiding and Cling and Ceiling and C'ling. More than one row of Units Watts per Watts per Watts per Watts per Square Foot Square foot Squere foot Square foot 1 ood ond aed 028 2 085 64 045 . 48 5 072 84 96 65 4 004 1.10 o 75 82 § 1.45 1.55 91 2.00 6 1.95 1.55 1.98 1.15 g 1.75 2.05 1.35 1.59 190 2.15 2.59 1.790 1.88 12 2.50 5 O00 1.98 2.2 Lé 2 00 oO 2.08 2,85 #*N, B. Bulletin. *# This table of Watte per Square Foot is based on the illumination requirements as shown in the classifisation Tables, pages 25 and 27. The number of each class is expressed directly in foot-candles. For the information of the engineer, it may be stated that the watts per square foot as given in this and following tables have been computed on the basis of the average lumens per watt for the most common sizes of Madda C lamps, and the approximate coefficient of utilization for the conditions assumed. An allowence has also been made to cover deprecia- tion in light output due to dust, etc. ~ & Class of Tlilumina- tion as Expressed in Foot Watts per Candles. foot 1 40 2 78 3 1.09 4 1.26 5 1.60 6 1.85 8 2.45 LO 2.8 “200 2 W. F. Bulletin. TABLE 15+ One Row of Units Light Walls Dark Walls and ceiling and c'ling Watts per foot — 57 1.10 1.40 1.80 2.25 2.60 5.50 4.290 5.90 Watts per foot 029 ® 5% 07S 9S 1.15 1.05 1.80 216 269 6q. For Mazda Daylight lamps increase these figures 50% Dark Walls and o'ling Watts per foot. 42 079 1.0§ 1.50 1.65 1.99 2.58 2 9S 0.65 Table of Watts per Square Foot for Stores, Offices, etc., When Illwainated with Totally Enclosing Units and Clear Mazda C Lamps. Hore than one row of Units. Light Walls and ceiling TABLE 16 # Table of Watts per Square Foot for Stores, Offices etc., When Illuminated with Indirect Units and Clear Mazda C Lamps. For Mazda Daylight lamps increase these figures 50% Class of One Row of Units Tllumina- Li tion as Light Walls Dark Walls Expressed and Ceiling and C'ling in Foot- Candles. Watts per Watts per eq. foot eq. foot ,43 82 1.10 1 40 Not re@- 1 «70 commend- 2.00 ed 2.65 5.20 5.80 wpoOeCaaeusr- ee eW. EB. Bulletin. More than One Row of Units. Light Wal&is Dark Wallis and ceiling and c'ling Watts per Watts per sq. foot sq. foot. 250 1.05 Kot re- 1.50 commend- 1.50 ed. Indirect lighting is especially dependent on the reflecting power of the ceiling and should not be used with dark colored ceilings. On the other hand, the reflecting power of the walls ocoes not make much difference in the illumination, and the values given above can be used with safety under most eonditions of walls. If, however, the walls are very dark and there is some question as to size of lamp the larger size should be used. wdez TABLE 17% Table of Watts per Square Foot for Stores, Offices, etc., When Illuminated with Semi-Indirect Units and Clear Mazda C Lanps. For Mazda Daylight lamps increase these figures 50% Class of One Row of Units More than One Row of Units Tllumina- tion as Light Walls Dark Walls Light Walis Dark Walls Expressed and Ceiling and C'ling anc Ceiling and C'ling. in Foot Candles. Watts per Watts per Watts per Watts per sq. foot eq. foot sq. foot sq. foot. 1 ~ 40 250 2 76 - 5 7 5 1.00 78 § 4.60 commend=- 1920 Gommend- 6 ‘1.85 ed 1.40 ed 8 2.45 1.88 190 2.95 2.20 12 3.50 2.65 *W. Z. Bulletin. Indirect lighting is especially dependent on the reflect- ing power of the ceiling and should not be used with dark colored ceilings. On the other hatid, the reflecting power of the walls does not make much difference in the illumina- tion, and the values given shove can be used with safety under most conditions of walls. If, however, the walls are very Gark and there is some question as to size of lamp the larger size should be used. 9 4% ode TA BLE 18 # Table of Watts per Square Foot for Stores, Offices, etc., When Tliuminated with Duplexalite Units and Clear Mazda C Lamps. For Mazda Daylight lemps increase these figures 50% One Row of Units More than One Row of Units Class of | Tlliumina- Light Walls Dark Walls Light Walls Dark Walis tion as and Ceiling and C'ling and Geiling and C'ling Bxpressed in Foot Watts per Watts per Watts per Watts per Candles. sq. foot sq foot Sq. foot sq. foot. 1 40 250 2 76 57 S 1.00 78 76 4 4.25 Not recom- 96 Not recom- & 1.60 mended 1.20 mended 6 1.88 1.40 8 2.45 1.85 20 2.95 2.20 12 5.50 2.65 “Ww, B. Bulletin. Duplex lighting is especially dependent on the reflecting power of the ceiling and should not be used with dark col- ored ceilings. On the other hand, the reflecting power of the walls does not make much difference in the illumination and the values civen above can be used with saefety under most conditions of walls. If, however, the walla are very dark and there is some question as to size of lamp the larger size should be used. Pea eee) a of ar | : 3 0008 p00 | 6009 002 Poot poe Oo DOr. 208. 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