Conspicuity for the rear of a vehicle is provided by rear position lights (also called tail lights). These are required to produce only red light and to be wired such that they are lit whenever the front position lights are lit, including when the headlights are on. Rear position lights may be combined with the vehicle’s stop lights or be separate from them. In combined-function installations, the lights produce brighter red light as stop lights and dimmer red light as rear position lights. Regulations worldwide stipulate minimum intensity ratios between the bright (stop) and dim (position) modes, so that a vehicle displaying rear position lights will not be mistakenly interpreted as showing stop lights and vice versa.
Red steadily lit rear lights, brighter than the rear position lights, are activated when the driver applies the vehicle’s brakes and warn vehicles behind to prepare to stop.
