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 154
HOTOMETERS 139 cited above is that where the horizontal distribution curvedeviates considerably from a circle so that a bad flicker resultswhen the lamp rotates at 180 r. p. m., some other method fordetermining the mean horizontal intensity should be employed.A fourth method of obtaining the mean… … Fig. 77.—Rotating mirrors. axis, the tip of the lamp being turned toward the photometerscreen. The two mirrors, inclined at approximately 90 degreesto each other, reflect to the photometer screen, light emittedfrom the lamp in a direction perpendicular to its axis. Thedirect rays from the lamp are…
Light · Photometry · Electric lighting
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