What is the function of the high-mounted stop lamp?

[VonGriffin]

The function of the high-mounted stop lamp is to warn vehicles behind, thereby avoiding rear-end collisions. Vehicles without high-mounted stop lamps, especially low-chassis sedans and micro cars, often have rear stop lamps positioned too low and with insufficient brightness during braking. This makes it difficult for drivers of following vehicles, particularly those with higher chassis like trucks, buses, and coaches, to see clearly. Consequently, there is a greater risk of rear-end collisions. Since most vehicles already have two stop lamps installed at both ends of the rear (left and right), the high-mounted stop lamp is also referred to as the third brake lamp, high-mounted brake lamp, or third stop lamp. The primary purpose of the high-mounted stop lamp is to alert vehicles behind, thus preventing rear-end collisions.