Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . asthe test lamp, or by removing the intercepting screen and themirrors and obtaining the constant of the apparatus by com-paring the horizontal intensity obtained in this way with thereadings obtained when the mirrors were in the horizontal planeand the screen in position. It is obvious that the position of themirrors as shown is merely to illustrate the construction and » Trans. Ilium. Eng. Soc, Vol. 6, p. 641, 1911. 142 LIGHT, PHOTOMETRY AND ILLUMINATION when in actual operation each is simila
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . asthe test lamp, or by removing the intercepting screen and themirrors and obtaining the constant of the apparatus by com-paring the horizontal intensity obtained in this way with thereadings obtained when the mirrors were in the horizontal planeand the screen in position. It is obvious that the position of themirrors as shown is merely to illustrate the construction and » Trans. Ilium. Eng. Soc, Vol. 6, p. 641, 1911. 142 LIGHT, PHOTOMETRY AND ILLUMINATION when in actual operation each is similarly 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 used instead of two, but two mir-rors offer an advantage in arc lamp photometry by reducing thefluctuations in intensity due to unsteadiness of the arc and thetraveling of the arc around the 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 and standard lamp are suspended from a track locatedabove the photometric axis. Reflected light due to the standardlamp is intercepted by opaque screens placed between the stand-ard lamp and the sight box and having openings along thephotometric axis large enough to let the direct rays pass photometrical balance may be obtained by changing the sizeof the openings in the rotating sector disk and varying the dis-tance between the standard lamp and the sight box. The sightbox should remain in the same position as when the apparatusis calibrated so that the incident angle of the light T
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
