Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . gle, then h = S cN direction, and c= ~ the distance in the other direction. bN The proper methods of spacing the lamps in a room are shown in and 161. Having settled the question of spacing the lightsources, the next item is the height of suspension. Uniform illu-mination is a good criterion to work for, and with the distance PRINCIPLES OF INTERIOR ILLUMINATION 263 between lamps established it follows that the minimum heightof suspension above the reference plane will be determined byth
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . gle, then h = S cN direction, and c= ~ the distance in the other direction. bN The proper methods of spacing the lamps in a room are shown in and 161. Having settled the question of spacing the lightsources, the next item is the height of suspension. Uniform illu-mination is a good criterion to work for, and with the distance PRINCIPLES OF INTERIOR ILLUMINATION 263 between lamps established it follows that the minimum heightof suspension above the reference plane will be determined bythe distribution of light from the unit chosen. At this point itAvould be well to refer to the polar curves near the end of ChapterIX and from the values of d/h given for ea^h polar curve onecan easily determine the height if the chosen unit has one ofthose types of distribution. Analyzing this phase of the subject Mr. Sweet (Ref. Cit.)has derived a set of curves, Fig. 157, showing the differentdistributions for d//i = A = l/2, 3/4, 1, 1 1/4, 1 1/2, and 2. In Apparent Candle-power40 60 80 100 120. Fig. 157.—Curves to give uniform illumination. (Two or more lamps.) other words, for uniform illumination, the maximum distancebetween lamps must not be more than 1/2, 3/4, etc., of theheight of suspension above the reference plane. Reflectors have been designed to meet the requirements ofthis class of service. The curves for 100, 150, and 250 wattlamps equipped with intensive and focusing types ofprismatic reflectors are shown in Figs. 158^ and 159^ of the extensive type shown in Fig. 155 may also beused for lighting interiors where it is desirable to place the lampseither lower or farther apart. Bui. 7 B, Nat. Elect. Lamp Assoc. 264 LIGHT, PHOTOMETRY AND ILLUMINATION For these three types of curves the relation of the distancebetween lamp centers to the height above the reference planefor approximately uniform illumination is: Extensive type curve, k^d/h =
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
