Optical mouse

An optical computer mouse uses a light source, typically an LED, and a light detector, such as an array of photodiodes, to detect movement relative to a surface. It is an alternative to the mechanical mouse, which uses moving parts to sense motion.

The earliest optical mice detected movement on pre-printed mousepad surfaces. Whereas modern optical mice work on most opaque diffusely reflective surfaces like paper, they usually aren't able to detect movement on specularly reflective surfaces like polished stone; coherently-lit (laser) mice can function even on such glossy surfaces, but perform poorly on transparent surfaces; dark field illumination allows mice to function reliably even on 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.