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what is a light

Light, electromagnetic radiation that can be detected by the human eye.
Electromagnetic radiation occurs over an extremely wide range of wavelengths, from gamma rays, with wavelengths less than about 1 × 10?11 meter, to radio waves measured in meters. Within that broad spectrum the wavelengths visible to humans occupy a very narrow band, from about 700 nanometers (nm; billionths of a meter) for red light down to about 400 nm for violet light. The spectral regions adjacent to the visible band are often referred to as light also, infrared at the one end and ultraviolet at the other. The speed of light in a vacuum is a fundamental physical constant, the currently accepted value of which is exactly 299,792,458 meters per second, or about 186,282 miles per second.


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