Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ough the45-degree mirror, E, a convex lens, and falls upon the upperhalf of the translucent screen, B. A comparison lamp, C,illuminates translucent screen, G. Light which is transmittedthrough this screen passes through a convex lens, the 45-degreemirror, E, the totally reflecting prism immediately above E, andfalls upon the lower part of the screen B, where it is viewed fromposition H. Both of the lenses just mentioned have adjustable > Trans. Ilium. Eng. Soc, Vol. 2, p. 546, 130 LIGH
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . ough the45-degree mirror, E, a convex lens, and falls upon the upperhalf of the translucent screen, B. A comparison lamp, C,illuminates translucent screen, G. Light which is transmittedthrough this screen passes through a convex lens, the 45-degreemirror, E, the totally reflecting prism immediately above E, andfalls upon the lower part of the screen B, where it is viewed fromposition H. Both of the lenses just mentioned have adjustable > Trans. Ilium. Eng. Soc, Vol. 2, p. 546, 130 LIGHT, PHOTOMETRY AND ILLUMINATION diaphragms, D and D\ which are used to vary the intensity andeffect equality of illumination upon screen B. The adjustmentof these diaphragms indicates the result of the photometricsettings. The comparison lamp, C, is a flat-flame gasoline instrument is calibrated by means of a Carcel lamp, whoselight falls upon the test-plate, A. The sector type photometer,* designed by Walter Bechstein, isshown in Fig. G7. The test-plate, A, is placed at the point where. Fig. 68.—The Lumeter. it is desired to study the illumination. This plate can be rotatedthroughout a vertical plane about the photometric axis. B isa Lummer-Brodhun cube through which the lower surface of thetest-plate, A, is viewed. Through the prisms, B, may be viewedalso the translucent plate G, which is illuminated by the com-parison lamp, C. Equality of illumination is obtained byvarying the size of the opening in the variable sector disk, D,and is determined by viewing the plate, G, through a portion ofthe lenses, F, which can be rotated. The result of the photo- Trans. Ilium. Eng., Soc, Vol. 2, p. 546, 1907. PORTABLE PHOTOMETERS 131 metric setting is indicated by the size of the opening in the disk,D. This device is in effect a rotating sector disk except thatthe beam of light instead of the disk is rotated, thus facilitatingprecise adjustment of the sector disk. The Lumeter is
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
