It is possible for many different spectral distributions to produce identical color sensations. A yellow color sensation may be caused by a single wavelength of light, for instance 590 nanometers, or it may be the result of viewing two single wavelengths such as 590 and 600 nanometers. It is also possible to view the color yellow as a narrow distribution involving all wavelengths between 590 and 600 nanometers. The same argument holds for all colors in the visible spectrum. Tungsten light sources are commonly labeled incandescent because they radiate light when heated by electrical energy.
Fluorescent light is generated as a result of electrical current traveling through a charged gas.
The red spectrum represents the relative energy of tungsten light over the visible spectrum. As is apparent, the energy of tungsten light increases as wavelength increases, which dramatically affects the average color temperature of the resultant light, especially when it is compared to that of natural sunlight and fluorescent light. The yellow spectrum represents what we see with a natural sunlight spectrum sampled at noon. Under normal circumstances sunlight would have the greatest amount of energy, but we have normalized the spectrum in order to compare it to the other two. The blue spectrum is seen with fluorescent light and contains some notable differences from the tungsten and natural sunlight spectra.