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 248
actually greater. Assuming, as a fair approximation, that the cosine law can beapplied, the integration for the total illumination at P, Fig. 134,will be performed. Application of Cosine Law.—Let Fig. 136 represent a length oftube and P be the point at which it is desired to determine… … Fig. 136.—Space diagram of positions. s = slant distance from P to tube, in feet./ = distance (parallel to tube) from P to element dl.CO — angle between ray P-dl and normal to reference plane.0 = angle between ray P-dl and normal to tube.(j) = angle subtended at P by the tube./? = angle between s…
Light · Photometry · Electric lighting
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