Once upon a time there was the brake light
07/21/2016
For many years, two (or sometimes even three or four) lights lit up at the back of a car when the driver stepped on the brakes. The lights were triggered by pedal pressure or the brake hydraulics.
They usually lit up regardless of the braking force; in principle, it was sufficient to touch the pedal.
Today, brake lights are often controlled by the vehicle electronics, with the brake signal going to the light via the control unit and CAN bus.
However, nowadays it is no longer just a matter of brake pulses triggered by the driver. With the advent of electric and hybrid vehicles and self-driving/braking cars (cruise control, adaptive cruise control), "brake lights" also indicate when the car is decelerating without actively applying the brakes, either because it is recuperating or because the speed has to be decelerated automatically due to a vehicle in front. Of course, this makes a lot of sense in terms of road safety, but it has little to do with the brake light used in the past. Just as little as the violently flashing brake lights of modern cars during emergency braking.
Incidentally, the first cars with brake lights are said to have appeared in 1905, before (and even after) the planned deceleration was indicated by hand signals. It would be many years before brake lights became standard. In 1928, only 11 states in the USA required brake lights. However, these were usually activated by the driver "by hand" and not by pressing the pedal. And the third brake light probably goes back to the psychologist John Voevodsky, who carried out tests with cabs in San Francisco in 1974.
