FAQ: Occupancy detection - What is the difference between presence and absence detection?
FAQ: Occupancy Detection - What is the difference between presence and absence detection?
Lighting control solutions often use occupancy detection methods to prevent lighting being left switched on unnecessarily, in order to reduce energy consumption and associated costs. The use of occupancy detection strategies can reduce the cost of lighting by up to 60% dependent on the usage of the room, level of occupancy and additional behaviours.
Occupancy detection solutions can be broadly split between presence and absence detection, which bring a number of benefits and limitations. It is important to consider the requirements of the different applications before deciding on the best solution for a particular space.
What is presence detection?
Presence detection is designed to reduce the amount of energy that lighting uses, by the lights only being switched on when the room is occupied.
For presence detection, sensors are used to detect occupancy within a defined zone. When a person enters the space, the sensor identifies that the room is occupied and the lights switch on automatically. Similarly, when the room is no longer occupied, the lights detect that the room is vacant and automatically switch off following a preset period of time.
Presence detection brings the benefits of increased energy savings and being a cost-effective solution as no wall switch is required.
What is absence detection?
Absence detection works in a similar way to presence detection, however this method generally provides greater energy and cost savings.
Absence detection typically works when a person switches on a light manually when entering the room. As the person leaves the room, sensors detect that the room is now vacant and the lights are switched off automatically, following a pre-determined amount of time. In addition, lights can be switched on or off manually to provide a local override.