Electromagnetic radiation in which wavelengths lie in the range from about 1 micrometer to 1 millimeter. This radiation therefore has wavelengths just a little longer than those of visible light and cannot be seen with the unaided eye. The radiation was discovered in 1800 by William Herschel, who used a prism to refract the light of the Sun onto mercury-in-glass thermometers placed just past the red end of the visible spectrum generated by the prism. Because the techniques and materials used to collect, focus, detect, and display infrared radiation are different from those of the visible, and because many of the applications of infrared radiation are also quite different, a technology has arisen, and many scientists and engineers have specialized in its application.