# Question #f08c3

Jan 4, 2018

Almost all kind of light sources if you restrict the definition of light to visible spectrum.

#### Explanation:

Light is by definition the visible part of electromagnetic radiation that has a wavelength between 400nm - 700 nm.

By this definition, most everyday light sources produce 700 nm light. They include fluorescent tube, incandescent light bulb, the sun, white LEDs, red hot heat plate (blackbody radiation), etc.

However, some people can see wider visible spectrum than others. So 700nm is not necessarily the limit to all people. If you restrict 700 nm as the longest visible light wavelength, you can find a LED that produces exactly this wavelength: see this 700 nm LED

Electromagnetic radiations such as infrared, microwave, and radio wave have longer and much much longer wavelength than 700 nm. The longest wavelength known is ${10}^{10} m$ . (Heirtzler, James R. "The Longest Electromagnetic Wave.", Scientific American. March 1962. (https://hypertextbook.com/facts/2001/RachelShapiro.shtml)