A car with a third brake light. Some cars have a third brake light, while others don't. Ever wondered why? Here's everything you need to know about a third brake light.

What Is A Third Brake Light For?

There are several laws governing automotive lighting, such as headlights, taillights, fog lights, and stop lamps, but what is a third brake light and what does it do? Automotive lighting serves three purposes: vision, visibility, and communication. This license plate bulb, for example, illuminates the license plate, helping to identify your vehicle.

  • Headlights improve your own vision, lighting roads and signs at night, and your visibility to other drivers, critical from about an hour before sunset to an hour or so after sunrise and in rain, snow, or fog.
  • Turn signals and stop lamps communicate your intentions to other drivers, so they can react properly to you turning or braking.
  • White, amber and red lamps also indicate the front and rear of your vehicle to other drivers.

What is a third brake light’s role in all this? Put most simply, the third brake light is a communication device, but we’re not talking about Morse code.

What Is a Third Brake Light in Relation to Stop Lamps?

Codified in the 1949 Geneva and 1968 Vienna Conventions, all vehicles are equipped with stop lamps.Third Brake Light Cars in Traffic Colloquially referred to as brake lights, they are installed in pairs at the rear corners of the vehicle. In North America, since 1986, all vehicles feature a third brake light. Legally, this is called the Center High Mount Stop Lamp, CHMSL for short, but informally called center brake lamp, high-level or eye-level brake lamp, cyclops brake light, or safety brake lamp.

Like stop lamps at the corners, the CHMSL indicates when the driver is braking, but its position and function add an extra layer of safety.

  • Positioned higher than the corner stop lamps, the third brake light is more visible to other drivers. The center brake light is usually located on the centerline of the vehicle, but may be offset if the vehicle features split rear doors.
  • Most vehicles feature an eye-level brake lamp which illuminates steadily whenever the driver is pressing the brake pedal. On some vehicles with combination stop-lamps/turn-signals, a steadily-illuminated CHMSL indicates braking, while the blinking stop lamp on either corner indicates the intended turn or lane change.
  • Depending on the vehicle, a blinking third brake light may indicate panic braking or initial braking.

What Is a Third Brake Light’s Effectiveness?

The third brake light improves visibility and driver-to-driver communication to reduce the occurrence and severity of rear-end crashes. After three decades of use, it’s hard to pin down how effective the CHMSL has been in these respects. Still, crashes occur every day, including rear-end collisions, anything that makes you more visible to other drivers is an improvement. Make sure your third brake light works as intended.

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

Photo courtesy of Flickr.

about author

Benjamin Jerew

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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