Light, photometry and illumination : a thoroughly rev. ed. of ''Electrical illuminating engineering'' (1912)
Barrows, William Edward, 1878-1960 · New York ; London : McGraw-Hill Book Co. · leaf 189
ofthe preceding equations. As already indicated the illuminationdirectly under the source would be £. = i-: m ^Electrical World, Vol. 55, p. 1215. May 12, 1910. 174 LIGHT, PHOTOMETRY AND ILLUMINATION or from the values indicated by the polar curve of Pig. 100 whenthe lamp is placed 8 ft. above the… … Fig. 100.—Graphical solution of the point-by-point method. where Ef^ = the horizontal illumination in foot-candles. la = the candle-power a degrees from the vertical.h = height of lamp above the working plane.d — distance from beneath the source. It will be seen that the polar diagram is…
Light · Photometry · Electric lighting
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