An electric eye is a photodetector used for detecting obstruction of a light beam. An example is the door safety system used on garage door openers that use a light transmitter and receiver at the bottom of the door to prevent closing if there is any obstruction in the way that breaks the light beam. The device does not provide an image; only presence of light is detectable. Visible light may be used, but infrared radiation conceals the operation of the device and typically is used in modern systems. Originally systems used lamps powered by direct current or the power line alternating current frequency, but modern photodetector systems use an infrared light-emitting diode modulated at a few kilohertz, which allows the detector to reject stray light and improves the range, sensitivity and security of the device.
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Famous quotes containing the words electric and/or eye:
“Persons grouped around a fire or candle for warmth or light are less able to pursue independent thoughts, or even tasks, than people supplied with electric light. In the same way, the social and educational patterns latent in automation are those of self- employment and artistic autonomy.”
—Marshall McLuhan (1911–1980)
“Loosed betwixt eye and lid, the swimming beams
Of memory, blind school of cuttlefish,
Rise to the air, plunge to the cold streams....”
—Allen Tate (1899–1979)