Automatic head light dimmer

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Thread Starter


Joined Feb 22, 2007
Our project aim is to dim head light in vechicles when opposite vechicle comes .This can be done by sensing light of opposite vehicle.

light should be dimmed when the Brightness of the opposite vehicle goes beyond our normal vision.which is 683 lumens/watt at 555nm.

I think LDR will be a suitable sensor for this.

Can anybody give circuit details and diagram. or any links that contain circuit.

Thanx in advance .....:)


Joined Feb 28, 2007
only problem with a light dependent resistor is that it might get confused my the car it is on's head lights otherwise its a great idea


Joined Mar 2, 2007
You're about 55 years too late ... it's been done. I worked in Cadillac dealerships for almost 20 years starting in the 60's and drove many cars with the feature. In fact, I had a friend with a '55 Chevy which he bought new .. it had one of those units also. Not too bad on desolate country roads, but a bit of a pain in the city or heavy traffic situations. I'm not positive but I believe the new Cadillacs again have a modernized version of the feature.

Here's some history I pulled off the net:

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.

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.


Joined May 16, 2005
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.
Not the kind of thing one wants in certain parts of Los Angeles...:eek:

LDR should work okay. Comparator might need some hysteresis to avoid the above scenario. Some kind of integration might also work.

The adjustment feature seems a good thing to me. My eyes are more sensitive to bright light in darkness than those of other folk I know. People just keep refusing to conform to those textbook figures!;)
On a nighttime car trip in 1949 from Cleveland to Washington, Rabinow came up with a solution to one of modern life's little irritations: the need for continual manual adjustment to the brightness of headlights. He patented 16 variations on his Automatic Headlight Dimmer. The main feature distinguishing his patents from patents on automatic dimmers by other inventors was the scanning system. This system prevented a photomultiplier behind it in the dimmer from integrating ambient light. It responded only to bright spots. A refinement on the original patent enabled the dimmer to distinguish the alternating current of bright street-lights from the direct current of bright automobile headlights. Although Rabinow's automatic dimmer was clearly superior to the few types then in use by car companies, no company was willing to purchase the rights to produce it. It would have cost them an extra dollar in materials because of its scanning system.


Joined Apr 20, 2004
Always check dates - the main thread stopped over a year ago.

I kind of question the one dollar amount. You speak of a photomultiplier tube. That in itself is more than $20 more than any CDS cell. Then you put in a scanning device plus some integration for ambient and the equivalent of a boxcar circuit to retain information on a bright spot? Plus a frequency-sensitive discriminator to ignore streetlights?

I think you may have a little convenience that might have cost several hundred dollars in production quantities and had problems with staying in operation. 1949 technology typically required a lot of tweaking to stay working.
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