TIA's Glossary of Telecommunication Terms
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light
In a strict sense, the region of the electromagnetic spectrum that can be perceived by human vision, i.e. , the visible spectrum, which is approximately the wavelength range of 0.4 
m to 0.7 m. (188) Note 1: In the laser and optical communications fields, custom and practice have extended usage of the term light to include the much broader portion of the electromagnetic spectrum that can be handled by the basic optical techniques used for the visible spectrum. Note 2: The region embraced by the term light has not been clearly defined, but by convention and usage, is considered to extend from the near-ultraviolet region of approximately 0.3 m, through the visible region, and into the mid-infrared region to approximately 30 m.