The third brake light is officially called the center high mounted stop lamp (CHMSL).
In everyday language, it's also known as the center brake light, center high-mount stop lamp, or simply the third brake light. This feature is designed to improve rear visibility and reduce collisions by signaling braking from a higher position.
Official terminology and regulatory background
Regulatory bodies standardize the name and installation. In the United States, the term CHMSL (Center High Mounted Stop Lamp) is defined under federal motor vehicle safety standard FMVSS 108. The CHMSL is typically mounted high at or near the top of the rear window or trunk lid, and can use LEDs, incandescent bulbs, or other lighting technology.
Placement and function
As a high-mounted light, the CHMSL provides a distinct, faster-visible signal to following drivers, especially in heavy traffic or during lane changes.
Common names and usage
People refer to this light by several names across regions and industries. The most widely used are:
- Center High Mounted Stop Lamp (CHMSL) — the official term in U.S. regulations.
- Center High Mount Stop Lamp — alternate wording.
- Center brake light / center brake lamp — generic term.
- Third brake light — common colloquial name.
- High-mounted stop lamp (HMSL) — another frequently used variant.
In practice, the official term varies by regulatory jurisdiction, with CHMSL used in the United States and "Centre High Mounted Stop Lamp" used in some European contexts; many people simply say "the third brake light" in everyday speech.
Historical context and design trends
Introduced as a safety feature to improve rear visibility, the CHMSL has evolved from incandescent bulbs to LED arrays in most modern vehicles. LEDs offer faster response times and greater reliability, helping to communicate braking more quickly to drivers behind.
Regulatory and design notes for drivers
When replacing or modifying a brake light, ensure any aftermarket units comply with local regulations and do not create glare or brightness issues that could distract other drivers or fail roadworthiness inspections.
Summary
The third brake light is officially known as the center high mounted stop lamp (CHMSL). It is a federally regulated feature in the United States and many other regions, designed to improve braking visibility. While it carries an official designation (CHMSL), it is also called center brake light, center high-mount stop lamp, third brake light, or HMSL depending on locale and context.