“Electric eye” is an old-fashioned term for a photodetector, an electronic circuit activated by light. First developed in the 1890s, this concept has been adapted to new devices and technology and is still in use in the 21st century. Common applications include remote controls, automatic doors, and motion detectors. This particular term has gradually faded from use at the end of the 20th century, although it was revived in 2009 to describe advances in artificial sight.
A photodetector operates by detecting the presence or absence of light or radiation of a similar wavelength, such as infrared (IR) radiation. The earliest photodetectors were designed in the late 19th and early 20th century. They used cathode tubes that released electrons in the presence of light, activating or deactivating a connected electrical circuit. The term “electric eye” was used to describe the device by comparing it to an eye, which also responds to light. Other terms included “magic lamp” and “magic eye.”
By the 1930s, the photodetector had multiple uses throughout the developed world. Safety devices use them to stop machinery if a worker crossed into a hazardous area. They detected intruders and counterfeit bills, security functions that are still in use today. Set to a certain color, which is determined by the wavelength of light, photodetectors could be used for sorting and quality control in industry. This same property allowed them to work with IR light, which is invisible to the human eye, making the device itself undetectable.
The once-novel electric eye had become a commonplace device by the last third of the 20th century. Familiar uses included automated doors in supermarkets and other public buildings and remote controls for garage doors and electronic devices. The concept was so useful that it was adapted to new technologies as the cathode tube became obsolete. Light-sensitive computer chips called photovoltaic cells eventually fulfilled the same function. Another consequence of the device’s ubiquity was the gradual disuse of the term.
In 2009, researchers into human sight announced a new prosthetic device for blind and sight-impaired people. This consisted of a microchip attached to the eyeball, where it could interface with the optic nerve. The chip detected signals sent from a face-mounted camera and transmitted them to the brain. The result did not fully restore sight, but at least allowed the user to detect shapes and faces. Media reports on the device naturally described it as an “electric eye.”
