How Do Automatic Headlights Work?

If you’ve ever driven a rental car at night and realized the headlights were set to “off,” you start to appreciate the automatic headlights you might have in your own car. Seeing and being seen in a vehicle have been paramount since the invention of the car itself, but headlights have come a long way.

And Then There Was Light

In the beginning, there was light — from an oil lamp, essentially. Electric lights started popping up around the turn of the century and, by the mid-1900s, automatic headlights could be found on some higher-end vehicles. Today, they’re more common and offer plenty of features that complement the automatic “on” and “off” — there’s automatic brightening and dimming and even light “bending” to help see around curves ahead.

Although headlights may seem straightforward, they’re important enough that further innovation is not just imminent, but necessary. They help show you the way and also show you to other drivers (without blinding them) while illuminating potential obstacles and dangers. In the end, anything dealing with safety is an area where improvement is always welcome.

This Little Light of Mine

Automatic lights are enabled through a system of headlight sensors — photoelectric sensors gauge ambient light and relay that information to the electronic control unit to turn the lights on and off as needed. These sensors are usually located on top of the dash where it meets the windshield. They can tell not only when the sun has gone down but also when you’ve entered a tunnel, garage or other low-light area.

There’s a small delay when switching automatic headlights on or off, which is sometimes controllable by the driver. Additional features, such as automatic brights and variable angles, are aided by cameras and additional sensors that can sense oncoming traffic, city lights and the turn of your steering wheel to adjust the direction of the beam.

The Shining

Even when they’re working perfectly, don’t take this feature for granted. Photoelectric sensors tell you about the presence of ambient light, but there are some situations, such as heavy fog, snow and rain, that require headlights, even during the day. These conditions won’t usually trigger your automatic lights when the sun is out, so you’ll need to remember to turn them on yourself. Daytime running lights won’t cut it because they aren’t as bright, and these systems don’t generally illuminate taillights. In bad weather, you want someone behind you with limited visibility to see you as soon as possible.

Most vehicles will tell you the status of your headlights on the dash, but there’s no default icon across manufacturers, so you really need to check out the owners manual to understand what your car is telling you. Automated systems are helpful, but they can never replace good, old common sense.

Check out all the headlight products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on automatic headlights, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photos courtesy of Blair Lampe.