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 261
s the brightness of ^S^ and co is the (small)solid angle subtended at P^ by S^; this is independent of theshape of Si or its distance from P^, The flux F passing throughdS at Pi is therefore F = hdajdS cos 0, over the area of S^ (1^) Or, F^hdsCcosO do) (168) Similarly, the flux due to dS at P^… … Fig. 147.—Surface source. As the same theorem holds for the elementary areas P, andP3, etc., it holds for their sum, and hence for a finite sui-face, S^(Fig. 147). Hence we see generally that the luminous flux due toa surface S^ passing through S^ is equal to the luminous flux due toS2 passing…
Light · Photometry · Electric lighting
Internet Archive · Boston Public Library · Public Domain Mark 1.0. Free to use for anything.
![An illustration from The American archaeologist [serial] (1898)](https://img.insideoutlibrary.com/img/200/ia-americanarchaeol02colu-15-8.webp)
