An electric eye is a photodetector

Photodetector

Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...

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

Garage door opener

A garage door opener is a motorized device that opens and closes garage doors. Most are controlled by switches on the garage wall, as well as by remote controls carried in the garage owner's cars, or more rarely, on keychains.- The electric opener :...

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

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

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

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 or the power line alternating current

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 frequency, but modern photodetector systems use an infrared light-emitting diode

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

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

• Also, 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 82 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 wave length was offered to businesses in need of a 24 hour alarm system.

External Links

• "Latest Way Beams Of Light Are Put To Work" Popular Mechanics, April 1931