An electric eye is a

photodetector Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or ...

used for detecting obstruction of a light beam. An example is the door safety system used on

garage door opener A garage door opener is a motorized device that opens and closes a garage door controlled by switches on the garage wall. Most also include a handheld radio remote control carried by the owner, which can be used to open and close the door from a ...

s 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 Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

radiation conceals the operation of the device and typically is used in modern systems. Originally, systems used lamps powered by

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...

or the power line

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

frequency, but modern photodetector systems use an infrared

light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

modulated at a few kilohertz, which allows the detector to reject

stray light Stray light is light in an optical system, which was not intended in the design. The light may be from the intended source, but follow paths other than intended, or it may be from a source other than the intended source. This light will often set a ...

and improves the range, sensitivity and security of the device.

Examples

Highway vehicle counter * In the 1930s, an electric eye vehicle counter was introduced in the US using two IR lamps set apart so that only cars and not pedestrians would be counted. First compact commercial unit * A compact type of electric eye was offered in 1931 that was enclosed in a small steel case and much easier to install compared to older models. Automatic wrapping machines * In the 1930s, an electric eye apparatus was developed to help a wrapping machine wrap 72 boxes a minute. Automatic door opener * In 1931, General Electric tested the first automatic door openers now popular in hospitals. They called their electric eye the ''Magic Eye''. Business alarm system * In 1931, an electric eye that used invisible UV wavelength was offered to businesses in need of a 24-hour alarm system. A system of this type is demonstrated in the first scene of the 1932 film '' Jewel Robbery''. Automatic cameras * In 1936, Dr.

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theor ...

and Dr. Gustav Bucky received a patent for a design which applied the electric eye to a camera. The camera was capable of automatically determining the proper aperture and exposure.Einstein invents automatic camera

Science News ''Science News (SN)'' is an American bi-weekly magazine devoted to articles about new scientific and technical developments, typically gleaned from recent scientific and technical journals. History ''Science News'' has been published since ...

Vol. 180 #6, September 10, 2011, p. 32.

References

External links

"Latest Way Beams Of Light Are Put To Work"
Popular Mechanics, April 1931 {{DEFAULTSORT:Electric Eye Optical devices Garage door openers

Examples

See also

References

External links