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:
“The family circle has widened. The worldpool of information fathered by the electric media—movies, Telstar, flight—far surpasses any possible influence mom and dad can now bring to bear. Character no longer is shaped by only two earnest, fumbling experts. Now all the world’s a sage.”
—Marshall McLuhan (1911–1980)
“He gives the impression of a strong mind which is composed and wise. His brown eye is exceedingly kindly and gentle. A child would like to sit in his lap and a dog would sidle up to him. It is difficult to associate his personality and this impression of kindness and gentle simplicity with what has occurred here in connection with these purges and shootings of the Red Army generals, and so forth.”
—Joseph Davies (1876–1958)