FAQ
Presence detector
What is a presence detector?
Presence detectors offer a range of functions to automate lighting. First and foremost is reliable movement detection. But presence detectors do much more than simply detecting movement – for example, they can switch on lights depending on thermal movement and ambient brightness. However, if the light levels are sufficient, the lights will not switch on, even if movement is detected.
Similar Questions
If your motion detector is no longer switching off, this may have several causes. End customers should cover all motion detectors on the system once. If all the devices are covered and the light goes off after the preset time, this means there is probably a heat source in the detection range of one of the devices.
If these measures are not successful, please contact your electrical engineering firm who will be able to help you find the error. You can find our dealer search tool here.
For passive infrared security lights, the following product families are available:
- Motion detectors (also called security lights)
- Presence detector
The similarity in the two device concepts is that the light switches on (depending on brightness levels) when movement is detected.
However, the differences between the two concepts result from the typical place of use and required switch-off behaviour.
For example, presence detectors are primarily built for ceiling installation in offices and switch off the lights when they are no longer needed, i.e. if it is either too bright or there is nobody there. The brightness is continuously measured and analysed when the lights are switched on. A presence detector also needs to detect small movements that are typical of office work and therefore requires a high-resolution detection field and a sensitive sensor.
Motion detectors are used to monitor corridors, access passageways, entrances, etc. The movements detected here are a lot more noticeable and high-energy and can therefore be detected more easily.
Outdoor areas have a lot more disturbances that must not be wrongly identified as movement by a security light. The response behaviour of security lights has been optimised for this purpose. The light only switches off (including in the case of security lights) when movement can no longer be detected – irrespective of brightness levels.
The primary purpose of a motion detector is therefore to switch on a consumer when it detects movement (e.g. for traffic route security). In contrast to this, a presence detector switches lighting off and thereby creates savings potentials (energy costs).
| Presence detector | Automatic control switch | |
| Switch-on behaviour | Depends on brightness | Depends on brightness |
| Switch-off behaviour | Depends on brightness | Does not depend on brightness |
Light sources such as light and halogen bulbs were developed to emit light radiation in the visible spectrum (approx. 400 to 800 nm); however, they give off the majority of the energy supplied in the form of heat radiation. Even discharge lamps (e.g. fluorescent lamps) give off a fairly substantial amount of radiant heat from their spiral filament. The intensity of these heat sources greatly exceeds the heat radiation given off by humans (see Fig. 1: heat radiation intensity of lights). For example, if a lightbulb is mounted within the detection field of security lights, switching off the light (from which point the light begins to cool down) may be detected by the security light as a change in heat. As a PIR security light cannot determine the source of a heat change, it switches back on. In order to avoid these “light swings”, the majority of security lights have a preset locking time. When the lights switch off, movement detection is blocked for approx. three seconds. A new movement can only be detected once this time has elapsed (see Fig. 2: Locking time after switch off). Note: Lamps and lights are not always fully cooled after three seconds, therefore, you should always ensure that there is a sufficient distance between the security light and other lights. If this is not possible, the security light detection field should be limited using covering panels or its sensitivity should be reduced (if possible).
You can use our TX_44 motion detectors outdoors at an installation height of 2.20 m The motion detectors with a 1.10 m installation height are not suitable here, as the devices do not have any natural boundaries and therefore could cause accidental alarm triggering.
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