A daylight sensor measures ambient light and provides a signal that a control system can use to switch or dim lighting. It is one possible input to adaptive or smart lighting. Availability and control behavior depend on the specific lighting system. The sensor can help avoid unnecessary lighting in bright conditions and maintain a chosen illumination level as daylight changes. Placement and calibration are important because shadows, dirt, reflected light, or the vehicle’s own lamps can affect the reading. The sensor normally forms one part of a larger control system rather than directly defining a lamp’s output.