Excerpt from Visual Acuity With Lights of Different Colors and Intensities
Along with the increase in intensity secured by the use of the improved types of lamps have come also wide variations in the hues of the lights in common use. The carbon filament incandescent lamp is the only one of the new types whose color tone approximates that of the old time gas flame. The variations extend from the brilliant white of the Welsbach mantle and the tungsten filament lamp to the strongly colored light of such sources as the mercury vapor arc and the flaming are, in which certain parts of the spectrum decidedly predominate, and other parts may be entirely lacking.
Further than this, the high intrinsic brightness of these recently developed types makes it possible to vary the hue at pleasure by the use of colored shades, which, notwithstanding their high absorptive indices, nevertheless transmit sufficient light to serve for ordinary purposes.
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