A light sensor monitors light levels and enables the automatic control of light scenes depending on available daylight. Using a lighting system in combination with changing daylight levels in rooms ensures a controlled illuminance, which is useful, for example, in order to maintain minimum values for workplaces or to reduce the radiation exposure on exhibits in museums. A daylight sensor on the roof (external sensor) measures the illuminance of the daylight and controls the lighting inside. If the light sensor is in the room (internal sensor), it measures the total illuminance of the incident daylight and the lighting in the room in order to control the light level depending on the daylight. The first process is referred to as open loop control, the second as closed loop control.
In combination with scene control, light scenes can be controlled depending on the daylight, for example, by using a twilight switch. In the same manner, the sensor control can be used to operate solar screening equipment.