Optical mouse

An optical computer mouse uses a light source, typically a light-emitting diode, and a light detector, such as an array of photodiodes or an image sensor, to detect movement relative to a surface. It is an alternative to the mechanical mouse, which uses moving parts to perform the same function. The earliest optical mice detected movement on pre-printed mousepad surfaces, whereas the modern optical mouse works on most opaque surfaces; it is usually unable to detect movement on specular surfaces like glass, although some advanced models can function even on clear glass. Laser diodes are also used for better resolution and precision. Battery-powered wireless optical mice flash the LED intermittently to save power, and only glow steadily when movement is detected. [Optical mouse. Wikipedia]