The third brake light, prominently positioned on most modern vehicles, serves a crucial safety function. While commonly referred to as the "third brake light," it goes by several other names, and understanding these, along with its history, purpose, and legal requirements, is essential for every driver. This guide provides a comprehensive overview of this vital automotive safety feature.

Third Brake Light: Nomenclature, Function, and Regulation

Term Description Significance
Center High Mount Stop Lamp (CHMSL) The technically correct and most widely accepted term. Refers to the light's central location and elevated position. Emphasizes the light's position for improved visibility to following drivers, reducing rear-end collisions.
Third Brake Light The most common and easily understood term. Describes the light's function as an additional brake light. Simple and intuitive language for everyday use and communication.
High-Level Brake Light Less common but still accurate. Highlights the light's elevated position relative to the standard brake lights. Emphasizes the visual separation from the standard brake lights, increasing its conspicuity.
Center Brake Light Similar to CHMSL, but less specific. Focuses on the light's central location. A shorter, less technical alternative to CHMSL, still conveying the central positioning.
Auxiliary Brake Light Describes the light as supplementary to the primary brake lights. Highlights the light's role as an addition to, rather than a replacement for, the standard brake lights.
LED Brake Light Refers to the type of bulb technology used in many modern third brake lights. Indicates the energy efficiency, brightness, and longevity benefits of using LEDs.
Rear Center Brake Light Specifies the location of the light at the rear and center of the vehicle. Provides a more precise description of the light's position.
Supplemental Brake Light Emphasizes the light's role in supplementing the primary brake lights, enhancing overall visibility. Underscores the added safety benefit provided by the third brake light in preventing accidents.

Detailed Explanations

Center High Mount Stop Lamp (CHMSL): This is the technically accurate and most formal term for the third brake light. It precisely describes the light's location, being centered on the vehicle's rear and mounted higher than the standard brake lights. The "stop lamp" designation clearly indicates its function as a brake light.

Third Brake Light: This is the most common and widely understood term. It simply refers to the fact that the vehicle has a third brake light in addition to the two standard ones located on either side of the rear of the vehicle. Its simplicity makes it easy to understand for the general public.

High-Level Brake Light: This term highlights the elevated position of the third brake light compared to the standard brake lights. The higher position makes it more visible to drivers in vehicles further back, especially in heavy traffic.

Center Brake Light: This term focuses on the central location of the light. While technically correct, it is less specific than CHMSL as it doesn't explicitly mention the elevated mounting position.

Auxiliary Brake Light: This term emphasizes the supplemental nature of the third brake light. It is an addition to the primary brake lights, providing an extra signal to following drivers.

LED Brake Light: This term refers to the type of light-emitting diode (LED) technology used in many modern third brake lights. LEDs are known for their brightness, energy efficiency, and long lifespan. Many older vehicles used incandescent bulbs, but LEDs are now the standard.

Rear Center Brake Light: This term provides a more specific description of the light's location, clarifying that it is at the rear and in the center of the vehicle. This is helpful in distinguishing it from other lights on the vehicle.

Supplemental Brake Light: This term highlights the light's role in supplementing, or adding to, the effectiveness of the standard brake lights. By providing an additional visual cue, it enhances safety and reduces the risk of rear-end collisions.

History and Development

The third brake light, or CHMSL, wasn't always a standard feature on vehicles. Its development and implementation are rooted in safety research and regulatory efforts aimed at reducing rear-end collisions.

  • Early Research: Studies in the 1970s and early 1980s demonstrated the effectiveness of a centrally mounted, high-positioned brake light in reducing rear-end collisions. These studies showed that drivers responded more quickly to a brake light positioned in their direct line of sight.

  • NHTSA Involvement: The National Highway Traffic Safety Administration (NHTSA) played a crucial role in mandating the CHMSL. Based on the research findings, NHTSA issued a Federal Motor Vehicle Safety Standard (FMVSS) requiring all passenger cars manufactured after September 1, 1985, to be equipped with a CHMSL. Light trucks and vans followed suit, with the requirement being phased in between 1994 and 1996.

  • Impact on Safety: The introduction of the CHMSL had a significant impact on road safety. Studies have consistently shown that vehicles equipped with CHMSLs experience a lower rate of rear-end collisions compared to those without. The improved visibility and quicker reaction times attributed to the CHMSL have saved countless lives and prevented numerous injuries.

  • Evolution of Design: Over the years, the design and technology of CHMSLs have evolved. Early models often used incandescent bulbs, but modern vehicles almost exclusively use LEDs. LED CHMSLs are brighter, more energy-efficient, and have a longer lifespan. Design variations include different shapes, sizes, and mounting locations, but the fundamental principle of a centrally mounted, high-positioned brake light remains the same.

Legal Requirements and Regulations

The presence and functionality of the third brake light are governed by federal regulations to ensure safety standards are met.

  • FMVSS 108: In the United States, the primary regulation governing vehicle lighting, including the CHMSL, is Federal Motor Vehicle Safety Standard (FMVSS) 108, "Lamps, Reflective Devices, and Associated Equipment." This standard specifies the requirements for the location, size, brightness, and color of the CHMSL.

  • Mandatory Equipment: As mentioned earlier, FMVSS 108 mandates that all passenger cars manufactured after September 1, 1985, and light trucks and vans manufactured between 1994 and 1996 be equipped with a CHMSL.

  • Functionality: The CHMSL must function properly whenever the standard brake lights are activated. It must be clearly visible and not obscured by any object.

  • State Laws: In addition to federal regulations, many states have their own laws regarding vehicle lighting. These laws typically reinforce the federal requirements and may include additional provisions.

  • Inspection Requirements: During vehicle inspections, the CHMSL is typically checked to ensure it is functioning correctly. A malfunctioning CHMSL may result in a failed inspection.

Benefits of the Third Brake Light

The third brake light offers numerous benefits that contribute to enhanced road safety.

  • Increased Visibility: The high-mounted, central position of the CHMSL makes it more visible to following drivers, especially in heavy traffic or adverse weather conditions.

  • Reduced Rear-End Collisions: By providing an additional visual cue, the CHMSL helps reduce the risk of rear-end collisions. Studies have shown a significant decrease in rear-end accidents in vehicles equipped with CHMSLs.

  • Faster Reaction Times: The CHMSL helps drivers react more quickly to braking vehicles, giving them more time to avoid a collision.

  • Improved Safety for Vulnerable Road Users: The increased visibility provided by the CHMSL also benefits pedestrians, cyclists, and motorcyclists, making them more aware of braking vehicles.

  • Enhanced Overall Safety: The CHMSL contributes to a safer driving environment for everyone on the road.

Troubleshooting and Maintenance

Like any other vehicle component, the third brake light may require occasional troubleshooting and maintenance.

  • Bulb Replacement: If the CHMSL stops working, the first step is to check the bulb. If the bulb is burned out, it needs to be replaced with the correct type. The owner's manual will specify the correct bulb type.

  • Fuse Check: If the bulb is not the problem, check the fuse that controls the CHMSL. A blown fuse can prevent the light from working. The fuse box location and fuse diagram can be found in the owner's manual.

  • Wiring Issues: In some cases, the problem may be due to wiring issues. Damaged or corroded wires can prevent the CHMSL from functioning properly. If you suspect a wiring issue, it is best to consult a qualified mechanic.

  • Lens Cleaning: Keep the CHMSL lens clean to ensure optimal visibility. Dirt and debris can reduce the brightness of the light.

  • Professional Inspection: If you are unable to diagnose or repair the problem yourself, it is best to take your vehicle to a qualified mechanic for inspection and repair.

Frequently Asked Questions

  • What is the main purpose of the third brake light? The primary purpose is to increase visibility and reduce rear-end collisions by providing an additional, centrally located brake light. It helps following drivers react more quickly to braking vehicles.

  • Is a third brake light required by law? Yes, in the United States, all passenger cars manufactured after September 1, 1985, and light trucks and vans manufactured between 1994 and 1996 are required to have a CHMSL. This is mandated by FMVSS 108.

  • What does CHMSL stand for? CHMSL stands for Center High Mount Stop Lamp. It refers to the light's central location and elevated position.

  • What type of bulbs are commonly used in third brake lights? Modern vehicles typically use LED (light-emitting diode) bulbs in their third brake lights due to their brightness, energy efficiency, and long lifespan.

  • What should I do if my third brake light stops working? First, check the bulb to see if it is burned out. If the bulb is good, check the fuse that controls the CHMSL. If neither of those is the problem, consult a qualified mechanic.

Conclusion

Understanding the various terms for the third brake light, its history, function, and legal requirements is crucial for all drivers. The "Center High Mount Stop Lamp" (CHMSL), "third brake light", or whatever name you choose, plays a vital role in preventing rear-end collisions and enhancing overall road safety, so keeping it functioning properly is paramount.