An automatic headlight dimmer (also called automatic beam control) was a device on automobiles which used a photoresistor to automatically adjust the headlight beams from "high beam" to "low beam" (ie. high and low brightness respectively) when encountering oncoming vehicles during nighttime driving, and to switch back to high beam after the vehicles had passed. Car redirects here. ... LDR A photoresistor is an electronic component whose resistance decreases with increasing incident light intensity. ... A SAAB headlight with combination projector/reflector optics A headlight or headlamp is a lamp, usually attached to the front of a vehicle such as a car, with the purpose of illuminating the road ahead during periods of low visibility, such as night or precipitation. ...

Drivers could also use standard headlight dimmers (such as foot-operated devices) to override the automatic headlight dimmer on cars so equipped.

General Motors "Autronic Eye" / "GuideMatic"

General Motors introduced the first automatic headlight dimmer – called the Autronic Eye – in 1952, on its Cadillac and Oldsmobile models; Buick, Pontiac and Chevrolet models began offering this feature in 1953. Cars with the Autronic Eye were easily identified by a periscope-like phototube that sat on the dashboard's left side, just inside the windshield. General Motors Corporation (NYSE: GM), also known as GM, is an American automobile maker with worldwide operations and brands including Buick, Cadillac, Chevrolet, GMC, Holden, Hummer, Opel, Pontiac, Saturn, Saab and Vauxhall. ... Cadillac is a brand of luxury automobile, part of General Motors, produced and mostly sold in the United States and Canada; outside of North America, they have been less successful. ... Oldsmobile was a brand of automobile produced for most of its existence by General Motors. ... Buick is a brand of automobile built in the United States, Canada, and China by General Motors Corporation. ... This article concerns the automobile; for the Native American leader, see Chief Pontiac, for other uses see the disambiguation page. ... Chevrolet Logo Chevrolet (IPA: ʃɛv. ...

One criticism of early automatic headlight dimmers – GM's Autronic Eye in particular – was that the headlights tended to erratically flicker between low- and high-beams in response to minor fluctuations of light, such as street lamps.

GM discarded the troublesome Autronic Eye after 1958 in favor of a revamped automatic headlight dimming system called GuideMatic. Introduced in 1959, the GuideMatic – which had a slimmer appearance than the Autronic Eye and sat at the left side of the dashboard, later moved to the center – had a switch that allowed drivers to adjust when the headlights dimmed. Though the GuideMatic system was an improvement over the Autronic Eye, many GM customers were leery through past experience and fears that the new system was still too erratic. By the mid-1960s, this feature was dropped on all GM models except Cadillac (which continued offering GuideMatic through 1988). In recent years, however, Cadillac once again began offering an automatic headlight dimming system. Cadillac is a brand of luxury automobile, part of General Motors, produced and mostly sold in the United States and Canada; outside of North America, they have been less successful. ...

Other makes

Later in the 1950s, Ford Motor Company and Chrysler Corporation began marketing their own automatic headlight dimmers. Ford Motor Company is an American multinational corporation and the worlds third largest automaker based on vehicle sales in 2005. ... The Chrysler Corporation was a United States-based automobile manufacturer that existed independently from 1925–1998. ...

• Ford Motor Corporation – An automatic headlight dimmer called AutoDim was offered on several Lincoln models starting in the mid-1950s, and eventually the Ford Thunderbird and some Mercury models had it available as well.
• Chrysler Corporation – Available corporate wide in 1959, top-line Chrysler and Imperial models offered its Automatic Beam Control dimmer throughout the 1960s and early 1969s.

Lincoln is an American luxury automobile brand, operated under the Ford Motor Company. ... The Ford Thunderbird is a car manufactured in the United States by the Ford Motor Company. ... -1... The Chrysler Corporation was a United States-based automobile manufacturer that existed independently from 1925–1998. ... 1955 Imperial Imperial was the Chrysler Corporations prestige automobile brand between 1955 and 1975, with a brief reappearance in 1981-1983. ...

See also