Optical sensors work by converting light into an electronic signal. The sensor is attached to a measuring instrument and an electrical trigger. When light strikes the sensor, it trips the trigger, so a measurement is taken.
The purpose of an optical sensor is to measure a physical quantity of light and, depending on the type of sensor, convert the readout for an integrated measuring device to display. Optical sensors can measure changes from several light sources at once, as in digital and electronic relays, making them common in automated industrial processes.
Optical sensors can be either internal or external. External sensors gather and transmit a required quantity of light, while internal sensors are more often used to measure bends and other small changes in direction.
For optical sensors to work effectively, they must be the correct type for the application, so that they retain their sensitivity to the property they measure. In addition they must not be able to measure any other property.
Optical sensors are integral parts of many common devices, including computers, copy machines and light fixtures that turn on automatically in the dark. Common applications include alarm systems, synchros for photographic flashes and systems that can detect the presence of objects.