How It Works: Automatic and adaptive headlights

Headlight technology has advanced radically in recent years, and this is how these automatic systems work

Author of the article:

You're reading: How It Works: Automatic and adaptive headlights

Jil McIntosh

How It Works: Automatic and adaptive headlights
Automatic high-beam headlights turn off when other traffic approaches or is driving ahead of the vehicle. Photo by Toyota

At one time, virtually all car headlights pointed only straight ahead, and you had to turn them on and off, and operate the high-beam headlamps all by yourself.


Today, automatic headlamps are commonplace, and even many entry-level models can automatically switch the high-beams when they detect oncoming traffic. And among many premium models, you’ll find headlights that “bend” when you’re turning so you can see around the corner.

Read more: BMW 750 Li Bulb Size Guide

None of these ideas are new, of course. General Motors offered automatic high-beam headlights, called Autronic Eye, in the early 1950s. Even earlier, a couple of cars had headlights that swivelled when turning, including the experimental and ill-fated Tucker. But in addition to being a lot more common, these modern systems depend on far more sophisticated technology.

Today’s automatic headlamps come on whenever the switch is in the “auto” position and it’s dark enough to require them. They use a photoelectric sensor that’s usually mounted on top of the dash, or on the windshield near the rearview mirror. On some vehicles, the owner’s manual may warn you not to place items such as papers on the dash. It’s because these can block the sensor and prevent the lights from working.


Most automatic headlights are set by the manufacturer, although some allow drivers to change the light sensitivity to how dark it must be before they’ll come on. Most don’t activate when it’s relatively bright but your lights should be on, such as when it’s raining, so be sure to switch them on manually in these situations. Your daytime running lights will be on, of course, but very few of them also illuminate the rear lights that other drivers need to see you in rain or snow. Mandatory changes are coming that will require front and rear lighting, but not for another couple of years.

More On This Topic

  1. How It Works: Highway structures
  2. IIHS’ latest top safety standards give auto industry a rough ride

Automatic high-beam headlights help solve two issues. They shut off the brighter lights as needed to avoid blinding occupants of oncoming vehicles. At the same time, since they turn the high-beams on when the road ahead is dark, they can help drivers who don’t always think to switch them on even when they can provide more illumination down the road.

Article content

Like automatic headlights, the system is driver-selectable. Most commonly, the driver leaves the high-beam switch on all the time and activates a second button for the automatic function. The system uses a forward-facing camera, usually mounted in or near the rearview mirror. The camera detects lights – not just oncoming headlights but also taillights of vehicles ahead, as well as streetlights or other illumination that indicates the driver is in the city and doesn’t need high-beams. As soon as other lights are detected, the system turns the high-beam headlights off, and then switches them back on again once the light disappears.

This automatic system is mostly for driving on rural roads or unlit highways where people often “overdrive” their headlights – travelling too fast for how far their low-beams illuminate ahead, so they can’t stop in time if something beyond their illuminated field of vision is on the road, such as an animal.

Article content

That’s also the basic idea behind adaptive headlights, which swivel from side to side, or up and down, to adjust for curves or elevation changes. Without adaptive headlights, the road ahead isn’t fully illuminated until you’ve turned the corner and you’re travelling straight again. Since adaptive headlights swivel in the direction you’re turning, you have a better view of what’s ahead and can see issues, such as a stalled car or someone trying to cross the road, before regular headlights would have revealed them.

How It Works: Automatic and adaptive headlights
Audi’s Matrix LED headlights can provide illumination for the driver without blinding other road users. Photo by Audi

The few old cars that had swivelling headlights used a mechanical connection to the steering gear to turn them. On modern cars they’re moved by small electric motors, which react to information provided by sensors that determine how fast the vehicle is going and how far the driver has turned the wheel. On some vehicles, supplementary cornering lights might come on to add extra lighting to the side of the road. The motors may also react to sensors that determine if the vehicle is going up an incline or into a dip, and move the lights up or down to keep the beams level.

Article content

Of course, technology is always forging ahead, and one of the goals with lighting is to eliminate as many moving parts as possible. Audi has computer-controlled LED headlights – not yet available in North America, thanks to our lighting regulations – that can selectively extinguish part of the lights, pinpointing the beams so accurately that the driver can have the benefit of high-beam headlights, but aimed so that they don’t affect other drivers.

Other companies are also improving their headlights. Hyundai is working on adaptive lights with pixels that form horizontal beams; sections of these can be lit or shut off to produce the “bending” effect of adaptive headlights without physically moving the lamps. And these improvements will be important even when cars drive themselves. Even if they use beacons and sensors, and won’t have to see each other, they’ll still have to be visible to pedestrians. High-tech or otherwise, headlights are sticking around.

How It Works: Automatic and adaptive headlights’s Blind-Spot Monitor

Sign up to receive’s Blind-Spot Monitor newsletter on Wednesdays and Saturdays

By clicking on the sign up button you consent to receive the above newsletter from Postmedia Network Inc. You may unsubscribe any time by clicking on the unsubscribe link at the bottom of our emails. Postmedia Network Inc. | 365 Bloor Street East, Toronto, Ontario, M4W 3L4 | +61404532026

Category: Headlights