Daylight efficiency of artificial illuminants . utlined curves and the axis ofabscissae are the resultant of increasing the ordinates of the sen-sibility curve in the proportion indicated by the curves of Fig. areas of the outlined curves are therefore proportional to theintensity of the unscreened sources, the shaded area to the intensityof the white light remaining after screening. The ratio of theshaded to the unshaded area gives the value Intensity of White Light obtained by Screening from .42/xIntensity of unscreened source. This quantity, for which the values for several sources ar
Daylight efficiency of artificial illuminants . utlined curves and the axis ofabscissae are the resultant of increasing the ordinates of the sen-sibility curve in the proportion indicated by the curves of Fig. areas of the outlined curves are therefore proportional to theintensity of the unscreened sources, the shaded area to the intensityof the white light remaining after screening. The ratio of theshaded to the unshaded area gives the value Intensity of White Light obtained by Screening from .42/xIntensity of unscreened source. This quantity, for which the values for several sources are givenin Table III, column 6, is an indication of the loss in efficiencywhich may be expected upon producing artificial daylight by theuse of colored absorbing screens. The figures also lend themselvesto giving a value to a light source considered from the standpoint ^ Abney, Phil. Trans. Roy. Soc. 193, p. 286; 1900. This curve is for high inten-sities where the Purkinje effect is not noticeable. Ives.] Daylight Efficiency of Illuminants. 237. .4 .5 .6 .7/^ •Fig. 2.—Excess of Colored Light in Various Li^ht Sources, Represented in Terms of Luminosity. 238 Bulletin of the Bureau of Standards. [Vol. 6, No. 2. of its approach in color to daylight. They may in fact be calledthe daylight or white light efficiencies, as is here done. TABLE Sensation Values, White Sensation and White Light Efficiencies. Source. 1 Glow lamp, carbon, watts per meanspherical cp Glow lamp, carbon, watts per meanspherical cp Glow lamp, metallized, watts per meanspherical cp Glow lamp, tantalum, watts per meanspherical cp Glow lamp, tungsten, watts per meanspherical cp Acetylene Welsbach mantle, f per cent cerium 8 j Mercury arc (Nichols) 9 Average daylight I 2 3 4 S Sensations. Lumi-nosity. Hue. Whitesensa-tion. Whitesen-sa-tion effici- Red. Green. Blue. ency. .588/t .588 .585
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