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 269
ingthe illumination on the test screen by which the intensity /„is measured. But for an extended disk, the quantity and the 254 LIGHT, PHOTOMETRY AND ILLUMINATION normal intensity, as we have seen above, are not the same.Thus, the quantity is b times the surface, or En = Q = 7za^b Q Jn 2 .2 ,.2… … Fig. 151.—Luminous circular disk. quantity Q is twice the normal intensity 7„. The total luminousflux is TzhS or - times the quantity, and the mean hemispherical Q intensity is — or half the quantity. In the case of a sphere of uniform brightness h the quantity is I hdS — Ana^h. The intensity…
Light · Photometry · Electric lighting
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