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 103
optical device whichpresents both sides of the screen to the eye as adjacent or con-centric fields. The Lummer-Brodhun photometer is built both as an equal- 88 LIGHT, PHOTOMETRY AND ILLUMINATION ity of brightness and as a contrast photometer. Thearrangement of each is essentially the same. The… … FiG. 32.—The Lummer-Brodhun equality of brightness photometer. ing through the telescopic tube 0 directed normally to B, clearlyviews a divided field illuminated partly by one source and partlyby the other. In the equality of brightness photometer the rays from I^ passdirectly through the central…
Light · Photometry · Electric lighting
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