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 sight of a planet through a telescope is worth all the course on astronomy; the shock of the electric spark in the elbow, outvalues all the theories; the taste of the nitrous oxide, the firing of an artificial volcano, are better than volumes of chemistry.”
—Ralph Waldo Emerson (1803–1882)
“The bottom line on bonding with multiples seems to be that if you see bonding as a static event—a moment in time at which you must have eye contact and skin contact simultaneously with two or more infants—you may indeed be in trouble.”
—Pamela Patrick Novotny (20th century)