Many people know that light passing through a prism separates into the colors of the spectrum.
Just as ripples on a lake can be close together or far apart, the waves that produce light vary in how closely they are spaces. Sunlight is made up of different wavelengths. The human eye is sensitive only to some of these wavelengths-the ones we see in the colors of the rainbow. Although near-infrared light is invisible, it behaves in a manner scientifically similar to that of light in the visible spectrum, and is therefore considered part of the optical spectrum. Although invisible, near-infrared wavelengths can be recorded on special sensitized film and by scanning instruments such as those on the Landsat satellites.