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 151
ce known as the illumination tester for obtain-ing an idea of the illumination of interiors is indicated diagrara-matically by Fig. 75.^ The illumination is received on the test-plate c which is viewed through an opening a in hg. Directlyabove a is located a convex lens d which focuses the light…
Light · Photometry · Electric lighting
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