Infrared Detection detects the movement of the human body by measuring infrared radiation (= heat) emitted by the human body and causes the luminaire to function. These detectors are said to be “passive” since they emit no radiation. The latter will be switched off if no other movement is detected during and after the selected time delay. The detection is done on an adjustable zone. A twilight cell is used to prevent the luminaire from being switched on when the selected brightness setpoint is reached.