Adaptive brake-lights are being equipped to help drivers reduce reaction time during emergency braking

Electric turn signal lights were invented as early as 1907, but were not widely offered by major manufacturers until after 1939. Hand signals were commonly used, though many vehicles had a semaphore signal. These were small, retractable mechanical side arms which were illuminated for indication.

These were generally mounted on the sides just behind the front door and swung out vertically. A non-self-cancelling lever on the dash was used to operate them. However, they had a tendency to break easily and were popular for some time, but not for long.

Until the early 1960s, most front-turn signals worldwide emitted white light and most rear-turn signals emitted red. Amber front-turn signals were voluntarily adopted by the auto industry for most cars beginning in the 1963 model.

At Mercedes-Benz, S-Class, developers also factored in drivers approaching from behind. They equipped the vehicle with adaptive brake-lights that begin flashing rapidly during emergency braking. Tests have shown that this signal reduces the time the drivers following behind take to react by 0.2 seconds.

This may seem insignificant, but it can make a crucial difference, reducing braking distance by 4.4m when the vehicle is travelling at 80kmph and 5.5 kmph at a speed of 100 kmph. The latter figure corresponds to the length of a typical sedan.

Turn signal lights must comply with technical standards that stipulate minimum and maximum permissible intensity levels. Their horizontal and vertical angles of visibility and minimum illuminated surface area should be designed to ensure that they are visible at all relevant angles. They should not dazzle those who view them, and should be suitably conspicuous in conditions ranging from full darkness to full direct sunlight.