The color of the light is determined by the light wavelength (or frequency). Certain wavelengths corresponding to a certain color. Solar radiation of the period of the wavelength of visible light range between about 0.76 microns to 0.4 microns, the corresponding color from red to purple, a total of 7 kinds of color, so the sun not monochromaticity. Launch a single color of light source is called monochromatic light source, light waves, it is a single wavelength. Such as krypton lamp, lamp of helium, neon, hydrogen light is monochromatic light source, such as fire only one color of light. Monochromatic light wavelengths of light, while a single, but there is still a certain distribution. Such as neon light emission only red light, good monochromaticity, known as the crown of monochromaticity, still have the range of 0.00001 nm wavelength distribution, so the neon red, identify carefully if still contains dozens of red. Thus, the wavelength of optical radiation distribution range is narrow, monochromaticity, the better. [2]

The wavelength of light, laser output distribution range is very narrow, so very pure color. With the output red light he-ne laser as an example, the wavelength of the light distribution can narrow the mu m level, the launch of the red light is krypton lamp two over ten thousand of the wavelength range. Thus, the monochromaticity of laser is far more than any kind of monochromatic light source.