The filament of light bulb glows incandescent as an electric current passes through it. We can observe the spectrum emitted by the filament by viewing the light through a transmission diffraction grating. The light bulb is attached to a variable power supply that allows the temperature of the bulb to be increased. At first the bulb glows faintly red with most of the light in the infrared region of the spectrum. As the temperature increases, the intensity of the light increases and more colors are seen in the spectrum. The peak of intensity of the spectrum shifts from red toward blue.
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