A laser beam and photoreceptors can be used to tell the difference between a smooth surface and a rough or matte surface with high albedo (low light absorbtion). A shiny surface, such as a sheet of polished metal or a pane of unfrosted glass, behaves according to the principle that the angle of reflection equals the angle of incidence relative to a plane tangent to the point of incidence. A matte surface, such as a sheet of printer paper, scatters incident light rays. If several photoreceptors are set up to capture reflected light, a shiny surface will reflect the beam back only to a receptor that is positioned in the path of the beam whose reflection angle equals its incidence angle. The matte surface will reflect the beam back to all the receptors.
A laser-based texture sensor cannot accurately measure the degree of roughness of a surface that is not shiny. A piece of printer paper reflects visible light in much the same way as a layer of flour, sand, or gravel. In addition, a visible-light-based texture sensor does not work well against rough or matte surfaces with low albedo. Such a surface, such as carbon black, produces a negative response at the photoreceptors. For surfaces of this type, high-speed electrons, infrared ( IR ) rays, or ultraviolet (UV) rays sometimes work. But efficient emitters and receptors of these forms of energy are expensive.