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 157
larly placed on oppositesides of a vertical line passing through the center of the sourceof light. Thus if it be desired to determine the candle-power15 degrees below the horizontal a mirror should be placed onopposite sides of the lamp 15 degrees below the horizontal. Obviously one mirror can be… … Fig. so.—Single-mirror Crane-type photometer. It will be seen from the figure that a rotating sector disk drivenby a small motor is placed in the photometric axis. This isused to increase the range of the apparatus by decreasing theintensity on that side of the photometric sight box. The sightbox…
Light · Photometry · Electric lighting
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