Fig. 7. The emission spectrum of a common incandescent (tungsten filament) light bulb is compared with a “cool white fluorescent tube.” The peak irradiation of the incandescent bulb lies much farther in the nonvisible infrared area of the spectrum than does the wavelength of the maximal irradiation of the fluorescent tube. This illustrates the relative efficiency of fluorescent lighting in producing visible light, whereas incandescent bulbs produce a much greater portion of nonusable heat.