It’s officially known as the Center High Mount Stop Lamp (CHMSL), commonly referred to as the third brake light.
Understanding the official name
The designation Center High Mount Stop Lamp describes both its function and its location: a brake signal placed higher than the rear tail lamps, usually centered on the vehicle’s rear. This elevated position helps following drivers notice braking sooner, especially when normal taillights are obscured by vehicles in adjacent lanes or cargo in the back. The everyday term “third brake light” remains widely used by drivers and in media coverage.
Regional terminology
While CHMSL is the formal term in the United States, regional variations exist. Some markets use High Mount Stop Lamp (HMSL) or Centre High Mounted Stop Lamp (British English spelling). In practice, “third brake light” is universally understood across many languages and nations.
Common regional terms used to refer to the feature include:
- Center High Mount Stop Lamp (CHMSL) — the formal US designation
- High Mount Stop Lamp (HMSL) — a shorter variant
- Centre High Mounted Stop Lamp — British/European spelling
- Third brake light — everyday, non-technical term
In practice, the exact wording varies by country and regulatory body, but the concept remains the same: a third brake light positioned higher up for better visibility.
Regulatory background
Safety regulators around the world mandate some form of third brake light to reduce rear-end collisions. In the United States, the National Highway Traffic Safety Administration (NHTSA) required CHMSL on all new light passenger vehicles beginning with the 1986 model year, under the Federal Motor Vehicle Safety Standard (FMVSS) 108. European and other UNECE member countries adopted analogous requirements during the late 1980s and early 1990s, leading to widespread standardization of center-high brake lamps across many markets.
A brief historical note
Early experiments with rear lighting showed that elevating a brake signal could improve recognition at a distance. Automakers incorporated this into production models through the 1980s and beyond, transitioning from incandescent bulbs to more durable LEDs in the 2000s and 2010s. Today, CHMSLs remain a proven — and often mandatory — component of rear lighting systems.
Design and technology
Today’s CHMSLs are typically mounted in a central location on the rear of the vehicle, frequently integrated into the hatch or trunk lid. Modern versions almost exclusively use LEDs for brightness, longevity, and quick response. Some designs incorporate dynamic features or micro-LED arrays that can improve visibility in bright daylight or with certain viewing angles.
Key design considerations include:
- Light source: incandescent bulbs (older cars) vs LEDs (modern cars)
- Positioning: centered high on the rear, often above the rear window
- Color and compliance: red is standard in most regions, with strict regulations against non-red colors for brake signaling
- Brightness and uptime: regulatory minimums for visibility and reliability
- Integration: sometimes a standalone module, sometimes integrated into the tail lamp cluster or the hatch frame
These design choices balance safety, cost, and aesthetics while ensuring the signal remains visible in a variety of driving conditions.
Practical impact and consumer awareness
For drivers, the CHMSL serves as a critical reminder to brake promptly when traffic ahead slows. For regulators, it remains a proven safety feature tied to rear-end collision reduction. Manufacturers continue to optimize CHMSL performance with energy-efficient LED tech and, in some cases, smart lighting features that respond to braking dynamics and ambient lighting.
Summary
The 3rd brake light is officially called the Center High Mount Stop Lamp (CHMSL) and is widely recognized as the third brake light. Originating from regulatory safety requirements in the 1980s, it remains a standard feature designed to enhance rear visibility and reduce crashes. Across markets, terminology may vary slightly (CHMSL, HMSL, Centre High Mounted Stop Lamp), but the concept and purpose are consistent: a higher, centralized brake signal that helps drivers see braking sooner.