The 321 Multisensor combines a light sensor for constant light control and a passive infrared (PIR) presence detector to provide energy-saving functions in a DALI system. The light sensor measures reflected light from the surface directly beneath it, using this information to maintain a constant light level by adjusting the lamp outputs. The PIR sensor enables the Multisensor to switch the lights on when its coverage area is occupied, and off when it is unoccupied.