Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . d it isoften sufficient to measure the illumination in a number of equalsections of a part of the total ^rea. Assuming that the result ofeach measurement represents the average intensity of that sec-tion, it follows that the average illumination will be the averageof these readings. The total light flux in lumens will equal the 182 LIGHT, PHOTOMETRY AND ILLUMINATION average intensity in foot-candles multiplied by the area In squarefeet. The method of laying off a room into sections for a test as
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . d it isoften sufficient to measure the illumination in a number of equalsections of a part of the total ^rea. Assuming that the result ofeach measurement represents the average intensity of that sec-tion, it follows that the average illumination will be the averageof these readings. The total light flux in lumens will equal the 182 LIGHT, PHOTOMETRY AND ILLUMINATION average intensity in foot-candles multiplied by the area In squarefeet. The method of laying off a room into sections for a test asexplained above, is illustrated in Fig. 105. The 15 lamps arelocated at 1, 2, 3, etc., as shown. It will be seen that the four-fourths of the room are similar, consequently one-fourth of theroom may be divided into sections and readings taken at a, b, c,d, etc., to obtain the average intensity for the room. It often happens, when all of the light is received from onelamp or cluster and where the class of service makes it impossibleto measure the illumination at the proper places, that a certain. Fig. 106.—Areas and test stations for circular equi-luminous areas. direction from beneath the source may be chosen along which theillumination may be measured, and the average intensity calcu-lated from these readings. The locations of test stations for asurvey of this nature are shown in Fig. 106 by the points a, h, c,d, etc. It is essential in a test of this nature that the distributionof light from the source be equal in azimuth and that the reflectedlight be proportionately distributed; in other words, the measure-ment at each station should represent the average intensity alongthe circumference of a circle drawn through that station with thepoint beneath the source as a center The representation, inter-pretation and calculation of the measurements thus obtained aregiven on the following pages. ILLUMINATION CALCULATIONS 183 The Representation of Results.—The results of calculat
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
