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It is seen that a source of radiant energy for heating human flesh to a depth should produce energy of 6,000 angstroms to 16,000 angstroms fairly efficiently. Tungsten-filament lamps are quite efficient sources of this long-wave visible and short-wave infrared energy. Inasmuch as human flesh is colored red by the blood, a red glass may be used for the bulb of a tungsten lamp. This greatly reduces the light without comparably reducing the energy which penetrates flesh. Even a cobalt blue glass transmits the deep red and the short-wave infrared energy quite efficiently.