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A person's face looks ghastly by the greenish light of a mercury-vapor lamp.

At night a large mercury-vapor lamp in the center of the room, supplemented by a number of well-placed incandescent electric lights, gives ample illumination.

In ordinary photographic printing tungsten lamps are widely used, but in blue-printing the white flame-arc and the mercury-vapor lamp are generally employed.

A red postage stamp looks greenish gray in the green light of a mercury-vapor lamp.