A mouse that uses light to detect movement. Introduced in the late 1990s, optical mice superseded mechanical mice because their sealed bottom surfaces have no mechanical parts to absorb dust and dirt. They work by emitting light from an LED or laser, and a CMOS sensor detects the light reflections as the mouse is moved. Early optical mice required a special mouse pad, but modern devices can be rolled over traditional pads, as well as over almost any surface other than glass or mirror. Laser-driven mice are even more tolerant of their surface than LED mice. Contrast with mechanical mouse.