Basic automatic headlights work through sensors that detect how much light is outside the vehicle. Most times, these sensors are located on the dash of the vehicle. The headlights turn on when the sensors detect a certain level of darkness.
Adaptive headlights are one type of automatic headlight. Adaptive headlights rotate when the vehicle is turning so that the road in front of the driver is always well lit. They use sensors to detect the speed of the vehicle, how far the driver has turned the steering wheel and the yaw, or the rotation of the vehicle around a vertical axis. Some adaptive headlights also sense when the brightness of the headlights needs to be adjusted. Generally, the sensors in adaptive headlights do not turn on if they are not needed, such as if the vehicle is parked or in reverse.
There are limitations to automatic headlights. Sometimes they do not turn on during heavy rain or fog, as the light sensor still detects enough light. Automatic headlights do not immediately turn on in cases of sudden darkness, such as if the vehicle drives through a dark tunnel. In these cases, it is important for drivers to use their best judgment and manually turn on their headlights if needed.