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 258
lement dS^ is hdS, cos e = 243 (IGla) as before. So also with the curved surface S^. In every case thegreater distance from P or the inclination of the angular positionis compensated by the greater area included within the given(imall) solid angle. Let us calculate the illumination at P due to a… … Fig. 143.—A large spherical source. of elementary solid angles. Each of the latter incloses an area,as S^, on the surface of the sphere, and also a corresponding areaSi, on the circular disk AB. As we have just seen, the illumina-tion produced at P by each spherical area Si, S^, etc., is exactlythe…
Light · Photometry · Electric lighting
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