^^mw^^Sm^^m. CODE OF LIGHTING SCHOOL BUILDINGS Copyright 1918 by ILLUMINATING ENGINEERING SOCIETY 29 Wert 39th Street, New Yofk, N. Y. |^0|,-;;^;;!>; PI CODE OF LIGHTING SCHOOL BUILDINGS Copyright 1 9 1 8 by ILLUMINATING ENGINEERING SOCIETY ii 29 West 39th Street. New York, N. Y. MAV 2\ ISI8 • CLA500081 PREFACE. There are 20,000,000 school children in the United States who are devoting several hours each day to study or to the per- formance of other work equally trying to the eyes. According to the available statistics nearly 10 per cent, of the number of school children examined are found to have defective vision. The severe requirements imposed upon children's eyes by mod- ern educational methods create need for the best of working conditions. Among these conditions lighting is of first import- ance. Improper lighting causes eye-strain, resulting in functional disorders, near-sightedness and other defects of the eyes. The following Code of Lighting School Buildings has been prepared by committees of the Illuminating Engineering Society in order to make available authoritative information for legisla- tive bodies, school boards and others who are interested in enact- ments, rules and regulations for better lighting. The requirements of the code as set forth in the Articles, are based upon good practice at the present time. Standards of illu- mination and other requirements are subject to revision by the Society with advances in the art of lighting. While the code is intended primarily as an aid in formulating legislation relating to the lighting of school buildings, it is also intended for school authorities as a guide in individual efforts to improve lighting conditions. Acknowledgment is made of the valuable co-operation of many members and non-members of the Society in the preparation of this code. Further information on this subject may be obtained by ad- dressing the Illuminating Engineering Society, 29 West 39th Street, New York, N. Y. CODE OF LIGHTING SCHOOL BUILDINGS. Article I. General Requirements. — When in use, all buildings should be provided, during those hours when daylight is inade- quate, with artificial light according to the following Articles. Buildings hereafter constructed should be so designed that the daylight in the work space is reasonably uniform and the dark- est part of any work space is adequately illuminated under nor- mal exterior daylight conditions.^ Article n. Intensity of Artificial Ulumination. — The desir- able illumination to be provided and the minimum to be main- tained are given in the following table :- Desirable and Minimum Illumination. Artificial lighting Foot-candles (Lumens per square foot)* At the work Minimum Ordinary practice t Storage spaces 0.25 0.5- 1.0 Stairways, corridors 0.5 1.0-2.5 Gymnasiums 10 2.0- 5.0 Rough shop work 1.25 2.0-4.0 Auditoriums, assembly rooms 1.5 2.5- 4.0 Class rooms, study rooms, libraries, labora- tories, blackboards 3-0 35- 6.0 Fine shop work 3-5 4-0- 8.0 Sewing, drafting rooms S-O 6.0-12.0 Article III. Shading of Lamps. — Lamps should be suitably shaded to minimize glare. Glare, either from lamps or from un- duly bright reflecting surfaces, produces eye-strain. * It should be borne in mind that intensity of illumination is only one of the factors on which good seeing depends. t Under the column headed "Ordinary practice," the upper portion of the range of in- tensities is preferable to the lower; where economy does not prohibit, even higher in- tensities than those cited are often desirable. 1 Daylight illumination values should be at least twice the values given in the Table Article II, for artificial lighting. » The illumination intensity should be measured on the important plane which may be the desk-top, blackboard, etc. The method of computing the flux of light (lumens) required to do any desired illu- mination is described under the heading "Design of I,ighting Installation" on page 12. For more specific information regarding the lighting of shops, see ''Code of Lighting Factories, Mills and Other IVork Places", issued by the Illuminating Engineering Society. 6 CODE OF IvIGHTiNG SCHOOIv BUILDINGS Article IV. Distribution of Light on the Work. — Lamps should be so arranged as to secure a good distribution of light on the work, avoiding objectionable shadows and sharp contrasts of in- tensities. Article V. Color and Finish of Interior. — Walls should have a moderate reflection factor; the preferred colors are light gray, light buff, dark cream and light olive green. Ceilings and friezes should have a high reflection factor; the preferred colors are white and light cream. Walls, desk-tops and other woodwork should have a dull finish. Article VI. Switching and Controlling Apparatus. — Basements, stairways, store rooms, and other parts of the building where required, should have switches or controlling apparatus at point of entrance. Article VII. Emergency lighting. — Emergency lighting should be provided at main stairways and exits to insure reliable operation when, through accident or other cause, the regular lighting is extinguished. Article VIII. Inspection and Maintenance. — All parts of the lighting system should be properly maintained to prevent deter- ioration due to dirt accumulation, burned-out lamps and other causes. To insure proper maintenance, frequent inspection should be made at regular intervals. NOTEIS — Data and Recommendations. DAYLIGHT. Intensity of Daylight. — In general, the minimum intensities of daylight illumination should be considerably greater than those provided in artificial lighting, owing to the adaptation of the eye to a much higher level of illumination (brightness) in the day- time. Direction of Light. — One of the fundamental rules for proper lighting of desks is to have the preponderance of light come from code; of IvIGhting school buildings u u u Ir^VrVr^^^^^ es'-o* . ELEVATION. ^ XE 31 DDDDnnnDn m DD D n D nn mnDDnnnn II D D D n D n D n mnnnnnnn Q -s-e'o" 1 A PLAN. Fig. I.— Unilateral daylighting. Scaled drawing of a typical modern class room. 8 CODE OF LIGHTING SCHOOI, BUII^DINGS the left side. For this reason many school authorities advocate unilateral lighting, that is, lighting by windows located on one side of the room only, especially for class rooms (see Fig. i). This method of lighting is recommended where the rooms do not ex- ceed about 24 ft. (7.9 m.) in width, with windows about 12 ft. (3.9 m.) high. If the rooms are much wider than this, bilateral lighting, that is, lighting by windows located on two sides of the room, may be required in order to provide sufficient illumina- tion in every part of the room and at the same time to prevent too great a diversity of contrast in the intensity of light on the work spaces. To secure the highest lighting value it is recommended that the room be so designed that no working location is more distant from a window than one and one-half times the height of the top of the window from the floor. Windows at the left and rear where practicable are preferable to those on the left and right sides of the room, because of cross shadows created by the latter arrangement. Lighting by over- head sources of natural illumination although sometimes used for assembly rooms, auditoriums and libraries, with relatively high ceilings, has ordinarily little application in class rooms and has found little favor in practice. The sky as seen through a window is a source of glare. For this reason the seating arrangements should always be such that the occupants (pupils) of the room do not face the windows. Window Openings. — Tests of daylight in well lighted school buildings indicate that, in general, the glass area does not fall below 20 per cent, of the floor area. As the upper part of the window is more effective in lighting the interior than the lower part, it is recommended that the win- dows extend as close to the ceiling as practicable. Lighting Value of a Window. — The lighting value of a window at any given location in the room, will depend upon the bright- ness of the sky, the amount of sky visible through the window at the given location in the room, and indirectly upon the reflection factor of the surroundings and the dimensions of the room. Observations in well lighted school rooms having a compara- tively unobstructed horizon, show that under normal conditions CODE OF LIGHTING SCHOOL BUILDINGS 9 of daylight, satisfactory illumination is usually obtained when the visible sky subtends a minimum vertical angle of 5° at any work point of the room. In cases in which the horizon is obstructed, as by adjacent high buildings or by high trees, provision should be made for a larger window area than would otherwise be required; also if need be, for redirecting the light into the room by means of prismatic glass in the upper sashes of the windows, or by prismed canopies outside of the windows. Window Shades. — Although direct sunlight is desirable in in- teriors from a hygienic standpoint, it is often necessary to exclude or diffuse it by means of shades. These shades should perform several functions, namely, the diffusion of direct sunlight, the control of illumination to secure reasonable uniformity, the elimi- nation of glare from the visible sky and the elimination of glare from the blackboards wherever possible. These requirements make it desirable to equip each window, especially in class rooms, with two shades operated by double rollers placed near the level of the meeting rail. The window shades may thus be raised or lowered from the middle, which provides the maximum elasticity for shading and diffusing the light. The shades should be prefer- ably of yellow-colored material that is sufficiently translucent to transmit a considerable percentage of the light while at the same time diffusing it. A more complete control of the light may be obtained by the use of two independent sets of shades at each window. Where two sets of shades are used, one should be preferably a very dark green of heavy material that will exclude the light entirely, and the other preferably a yellow-colored material as above described. Different views of a window equipped with a single set of ad- justable shades as used in the public schools of New York City are shown in Fig. 2. It will be noted that this method of in- stallation permits of lowering the window from the top or raising it from the bottom without interference with the shades. Light Courts. — Reflection of light from the walls of courts is very helpful in increasing interior illumination. Hence the walls of courts should have high reflection factors. Dark colors should be avoided. lo code; of lighting school buildings Maintenance. — Windows and overhead sources of natural light (so-called skylights) should be washed at frequent intervals and surfaces such as ceilings and walls should be cleaned and refin- ished sufficiently often to insure their efficiency as reflecting sur- faces. It should be borne in mind that the maintenance of ade- quate daylight indoors is also dependent upon various external factors, such as the future erection of buildings and the growth of trees or vines. ARTIFICIAL LIGHT. Systems of Xighting. — It is customary to divide the systems of artificial lighting into three classes, namely, direct, semi-indirect, and indirect. This division is arbitrary and the boundary lines are quite indefinite. A direct lighting system is known as one in which most of the light reaches the work plane directly from the lighting unit including the accessory which may be an opaque or glass reflector or a totally enclosing transparent or translucent envelope. Direct lighting systems may be further classified as localized and general or distributing. In the former the units are so placed as to light local work spaces, and in the latter they are well distributed so as to light the whole area more or less uniformly. A semi-indirect system, is know^n as one in which a portion of the light reaches the work plane directly from the unit and a relatively large portion reaches the work plane indirectly, by reflection from the ceiling and walls. The accessory is usually an inverted diffusing bowl or glass reflector. When this glass has a high transmission factor the lighting effect approaches that of ordinary direct lighting, and when of low transmission, the effect approaches that of indirect lighting. An indirect system is known as one in which all or practically all the light reaches the work plane indirectly after reflection from the ceiling and walls. The accessory is usually an opaque or slightly translucent inverted bowl or shade containing a re- flecting medium. All three of these systems of lighting (illustrated in Figs. 3, 4, and 5) are in successful use in schools. There has been a grow- ing preference for semi-indirect and indirect lighting, especially since the introduction of modern lamps of great brilliancy. Local lighting by lamps placed close to the work is unsatisfactory ex- Fig. 3. — Good direct lighting. In general, semi-indirect or indirect lighting is better for .school rooms. Fig. 4. — Good indirect lighting. Fig. 5 — Good semi-indirect lighting. Kig. 6. — Bad lighting. The lighting units are hung too low and the light sources are not adequately shaded. Note the glossy varnished surfaces on benches and woodwork. Fig. 7.— Bad lighting. The local lamps, if used at all, should be provided with reflecting shades to protect the eyes from glare and at the same time to direct the light to the work. General illumination by overhead units is preferable. 8.— Bad lighting. The use of local lighting by adjustable table lamps usually results in glare from lamps on neighboring tables; also in annoying shadows. The difficulties may be overcome by the use of a system of general illumination. CODE OF LIGHTING SCHOOL BUILDINGS II cept for special cases such as the lighting of blackboards, maps, charts, etc. Examples of bad lighting are shown in Figs. 6, 7, and 8. Shading of Lamps. — Except in very rare instances bare light sources should not be exposed to view. They should always be adequately shaded or completely hidden. Even when shaded by translucent media, such as dense glassware, the lighting units should be placed well out of the ordinary range of vision; in other words it is recommended that lighting units be of low brightness,^ even if they are located high in the field of view. The maximum brightness contrast of juxtaposed surfaces in the normal visual field should be preferably not greater than 20 to I ; that is to say, the darkest part of the work space observed should have a brightness preferably not less than one-twentieth of that of the brightest part. Glossy Surfaces and Eye-Strain. — Glossy surfaces of paper, woodwork, desk-tops, walls and blackboards are likely to cause eye-strain because of specular or mirror-like reflection of images of light sources, especially when artificial light is used. Matte or dull finished surfaces are recommended. It is to be noted that a high reflection factor does not necessarily imply a polished or glazed surface. To minimize eye-strain it is recommended that unglazed paper and large plain type be used in school books. • Preferably not to exceed 250 tnillilamberts. A millilambert is equal to the bright- ness of a perfectly reflecting and diffusing surface illuminated to an intensity of 0.929 foot-candle, (0.^29 lumen per square foot). It is also equal to 0.002 candle per square inch. The foMowing table shows the order of magnitude of the brightness of some light sources in common use: Approximate brightness Indirect lighting: ceiling, directly above the light- ing unit Semi-indirect lighting: heavy density glassware . " " " light density glassware . . Direct lighting: 10 in. (25 cm.) opal glass ball con- taining loo-watt vacuum tungsten lamp at center " " vacuum tungsten lamp, (frosted) in open bottom reflector .... Vacuum tungsten lamp, filament exposed to view . Gas-filled tungsten lamp, filament exposed to view Gas-mantle, bare " " concealed in 6 in. (15 cm.) opal glass globe 1,000. 2. Mercury arc tube (glass) 8,000. 16. Daylight: clear blue sky i,ooo. 2. Millilamberts Candles per sq. in. 5- to 75. o.oi to 0.15 35. to 100. 0.07 to 0.2 200. to 1,000. 0.4 to 2.0 250. to 500. 0.5 to I.O 2,000. to 3,000. 4. to 6. 500,000. I, ,000. 2,000,000. 4 ,000. 15,000. 30. 12 CODE OF UGHTING SCHOOL BUILDINGS Children should be taught to hold their books properly, to as- sume a correct position relative to the light source, and to safe- guard their vision. Color of Light. — It has been found in practice that the admix- ture of daylight and artificial light is not satisfactory unless the latter is derived from lamps designed with special reference to producing daylight color values. Hence in w^aning daylight it is desirable to shut out the daylight and to use artificial light exclusively unless the lamps are of the type mentioned. Design of Lighting Installation. — The illumination intensity on the horizontal v^ork plane should be as uniform as possible. The variation should not be greater than 4 to i.'* Approximate Coefficients of Utilization— Modern Lighting Equipment. Small Rooms (Offices, Corridors, etc.). I,ight color Medium color walls walls l,ight color ceiling Light color ceiling Direct lighting; dense glass (open bottom reflectors) 0.40 0.3S Semi-indirect lighting; dense glass c.25 O.22 Indirect lighting 0.23 0.20 Medium Sized Rooms (Class Rooms, Laboratories, etc.). Direct lighting; dense glass (open bottom reflectors) 0.50 0.4S Semi-indirect lighting ; dense glass 0.35 0.30 Indirect lighting 0.30 0.25 Large Rooms (Auditoriums, etc.). Direct lighting; dense glass (open bottom reflectors) 0.62 0.60 Semi-indirect Ughting ; dense glass 0.43 0.40 Indirect lighting 0.40 0.38 The chief factors which must be considered in arriving at the size and number of lamps to be used in a given room are ( i ) the floor area; (2) the total luminous flux^ emitted per lamp, and * This ratio refers to the light received by the object illuminated and should not be confused with the ratio of 20 to i for brightness contrast previously given on page 10, which refers to the light radiated by the object. For example, a blackboard and a white sheet of paper on it may receive the same amount of light, but the latter will reflect much more light than the former, thus causing a marked brightness contrast between the two surfaces. 6 The flux is measured in lumens. A lumen is the unit of light flux and is the quan- tity of light required to illuminate i square foot of area to an average intensity of i foot- candle. CODE OF UGHTING SCHOOL BUILDINGS 13 (3) coefficient of utilization of the particular system considered. The first should be measured in square feet. The second may be obtained from a data book supplied by the manufacturers of lamps. The third involves many factors such as the relative di- mensions of the room, the reflection factor of the surroundings, the number of lighting units and their mounting height, and the system of lighting. By coefficient of utilisation is meant the pro- portion of the total light flux emitted by the lamps which is ef- fective on the work plane. In the accompanying table ap- proximate coefficients of utilization for modern lighting equip- ment are given. The work plane in this case is a horizontal plane 30 in. (76 cm.) above the floor. These values refer to the initial installation without any allowance for depreciation. For determining approximately the size and number of lamps to be used in a given room by means of the coefficients of utiliza- tion given in the preceding table, it is necessary to know the lumi- nous output in lumens per watt for the electric lamps considered or in lumens per cubic foot of gas consumed per hour if gas lamps are considered. At the present time (191 7) the light output of tungsten filament electric incandescent lamps, based on average service conditions of regularly maintained installations, ranges from 8 lumens per watt for the smaller vacuum tungsten lamps to 14 lumens per watt for the larger gas-filled tungsten lamps em- ployed in school lighting. For incandescent gas systems similar service values range from 150 to 250 lumens per cubic foot of artificial gas consumed per hour. The computation for the total lumens required to give a certain illumination intensity in foot- candles is as follows: N = number of lamps. L, = lumens output per lamp. E = coefficient of utilization. A = area of floor or horizontal work plane in square feet. I = illumination intensity in foot-candles. N X LXE ^ A that is, the number of lamps multiplied by the output per lamp in lumens, multiplied by the coefficient of utilization, divided by the area of the horizontal work plane in square feet, gives the illumination intensity in foot-candles. 14 CODE OF UGHTING SCHOOL, BUILDINGS If the size of the lamps is to be ascertained the computation is made thus : ^ I X A ^ NXK To illustrate by an example, assume a room, whose floor (also work plane) is 30 ft. by 18 ft. (9.1 by 5.5 m.), to be lighted by a semi-indirect system from six fixtures containing one lamp each. It will also be assumed that the ceiling is highly reflecting, the walls moderately reflecting, and the illumination intensity de- sired is 5 foot-candles. The luminous output required of each of the six lamps will be found by substituting the assumed values in the equation, thus : 5 X 30 X 18 , L = = I , SCO lumens 6 X 0.30 '^ Allowing a depreciation factor of 20 per cent, as representing a well maintained installation, the lumens actually required would Ije h^^ = 1,875 lumens. If gas-filled tungsten lamps are con- 0.8 sidered, whose average output under service conditions is 12 lumens per watt, it is seen that a 150- watt lamp in each fixture will give the desired results. If gas mantle lamps are considered, whose average output in lumens under service conditions is 250 lumens per cubic foot of gas consumed per hour, it is seen that a lamp consuming 5 cubic feet of artificial gas per hour will be satisfactory in each fixture. The above example is intended solely to illustrate the method of computation. Estimates of the illumination intensity obtained from an actual installation may also be made by a similar com- putation. Suitable switching and controlling arrangements should be made to permit of lighting one or more lamps independently as conditions may require. The teacher's desk may be illuminated by one of the overhead lighting units, or if necessary, by a desk lamp. With the usual lighting equipments the distance between the units should not exceed one and one-half times the height of the apparent source of illumination above the working level. CODE OF LIGHTING SCHOOL BUILDINGS IS Blackboards. — Blackboards should be of minimum size prac- ticable and should not be placed between windows. Their posi- r- *^ C — ^-- ^ — -/4^ ^^^=^[ ^ ^^r^" La^ r^l Fig. g. — Diagrammatic illustration of glare from blackboards, (a) Showing that occupants of seats in shaded area are subjected to daylight glare from blackboards. (i) Showing angles at which glare is experienced from daylight and from artificial light. (c) Arrangement of local artificial lighting to minimize glare. tion should be carefully determined so as to eliminate the glare due to specular reflection of images of either artificial or natural light sources directly into the eyes of occupants of the room. The surface of blackboards should be as dull as possible and this dullness should be maintained. i6 CODE OF LIGHTING SCHOOL BUILDINGS Glare, due to specular reflection from blackboards, may be re- duced or eliminated by lighting them by means of properly placed and well shaded local artificial light sources. In Fig. 9 are shown some simple graphical considerations of blackboard lighting. In (a) is shown a plan view of a room with windows on one side. Rays of light are indicated by A, B and C in a horizontal projection. These are supposed to come from bright sky. By the application of the simple optical law of re- flection — the angle of incidence is equal to the angle of reflection — ^it is seen that pupils seated in the shaded area will experience glare from the blackboards on the front wall. In (&) is shown the vertical projection of the foregoing condition. It will be ap- parent from this graphical illustration that by tilting the black- board away from the wall at the top edge, the pupils in the back part of the room will be freed from the present glaring condition. Whether or not this tilting will remedy bad conditions may be readily determined in a given case. In (&) the effect of specular reflection of the image of an artificial light source is shown by D. In (c) is shown a proper method of lighting blackboards by Fig. 10 (a). — Old artificial lighting equipment. means of artificial lighting units. This will often remedy bad daylight conditions whether due to an insufficient illumination in- tensity of daylight or due to reflected images of a patch of sky. In order to avoid excessive brightness contrast which is try- ing to the eyes, blackboards should not be placed on a white or highly reflecting wall. Rehabilitating the Lighting of Old Buildingfs. — This will be il- lustrated by an actual case where the artificial lighting of a class CODE OF LIGHTING SCHOOL BUILDINGS i7 room was made satisfactory at a small expense. In Fig. lo (a) is shown an elevation of a section of the class room showing the old fixtures. In Fig. lo (c) the circles containing crosses (^) indicate the positions of the two old fixtures in this room. The chief objections to this old system were as follows: (i) The lighting units were hung too low, so that eye-fatigue resulted from the bright sources in the visual field. ^ TJ-V 7 10- 0' TKS^^S, 3- J" 3-9' Fig. to (i).— New artificial lighting equipment. :0::GM;D::0:Ln::0::n:i0 . r-h' D::E:@:E;r ■-L \^ a;:di0:n:i!n:;E:n ! ^ .f '^E:"n:"SJn";B::n:i0 4r B::aia::D:i 0::d.t0:n:srM:B::q:»" - /O' [— h4- 8-9' 1 *\* 8-9" ■ I H* 7'/ 5--I0" !n"E:d:[0 . Fig. 10 (c).— Old ( ?5^ ) and new ( (j ) outlets for artificial lighting equipment in a class room. i8 code; of lighting school buildings (2) The light sources were not shielded from the pupils' eyes. (3) Two fixtures are insufficient to provide satisfactory il- lumination over the entire work plane in a room of the dimen- sions shown. This unsatisfactory condition was remedied by means of six fixtures placed as indicated by the circles (]2^) in Fig. 10 (c). These fixtures, shown in elevation in Fig. 10 (&), consisted of inverted diffusing glass shades containing one lamp each. The dimensions of the room are shown in the illustration. Maintenance. — A systematic maintenance should be provided in order to insure against depreciation in the illumination inten- sity due to burned-out lamps, broken gas mantles, discoloration, etc., and to accumulations of dirt upon the lamps, and upon the surfaces of the reflecting and transmitting media. It is found in practice that carelessness in this respect may easily reduce the effective illumination by 50 per cent., especially in indirect and semi-indirect lighting. Issued Apiil 30, 1918. ««•. w'Ti ;■■'■■ ' SiP a 2 1»