Versatile and efficient Technology from Theben

Presence detectors for
energy-efficent lightning control

With Theben presence detectors, you have every option for energy-efficient and intelligent lighting control. In addition to classic use for lighting control in offices, corridors and public buildings, you can also control heating and air-conditioning based on presence. This lets you save energy costs and considerably reduce CO2 emissions. Presence detectors react to the slightest of movements and measure room brightness at the same time. If no more movement is detected, or a defined brightness value is exceeded, the presence detector automatically switches off the light.


Technology: How does a presence detector work?

Presence detectors work according to the same principle as motion detectors: They detect thermal radiation in their surroundings, that is, in their detection area. If thermal radiation is detected in the detection area, for example caused by a person approaching the presence detector, the detector converts the radiation into a measurable electric signal, and the light is switched on.

The difference between motion and presence detectors lies in the sensitivity of the sensors. Presence detectors have much more sensitive sensors than motion detectors and detect the smallest of movements. The sensitive sensors divide the detection area of a presence detector evenly into up to 1000 zones. Like a chessboard, the zones run through the entire detection area. Even slight changes in the thermal image, such as typing on the keyboard in an open-plan office, will be detected. In contrast, a motion detector only responds to greater changes in the thermal image and is therefore mainly suited for applications with larger, walking movements or outdoor use. A further difference between motion and presence detectors lies in the light measurement. A motion detector measures brightness once, when the light is switched on because of a movement. If it continues to detect movements, e.g. in the morning in an office, the light remains switched on even though daylight would be sufficient in the meantime and the set brightness value has already been exceeded. This means the light remains switched on unnecessarily. In contrast, presence detectors constantly measure the brightness: if a defined brightness value is exceeded, the presence detector switches the light off, even if it detects movement. This reduces energy costs and significantly lowers CO2 emissions.


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Square detection area of 360º

As most rooms are square or rectangular, a square detection area simplifies planning enormously. The detection areas of the individual presence detectors can be lined next to each other with no gaps. In addition to simplified planning, there is another practical benefit in that there are no "blind spots" or overlaps in the room. And movements are guaranteed to be reliably detected everywhere.

In contrast to presence detectors with a circular detection area, presence detectors with a square detection area ensure optimum coverage of rooms without unnecessary overlaps or gaps.


Light measurement in detail

Lighting control using presence detectors is based partly on detected movement and partly on light measurement. Presence detectors constantly measure the brightness inside the room. Through such continuous light measurement, the presence detector is able not only to switch on artificial light when there is not enough daylight, but also to switch off lighting again when daylight is sufficient. It sounds very simple, but in fact the presence detector must be able to assess, while the artificial light is still on, whether there will be enough daylight after switching it off.

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Switching mode

During switching operation, the presence detector measures the sum of artificial light and daylight. To switch off the artificial light when there is increasing daylight at the right moment, the presence detector must know the proportion of artificial light. This value is automatically learned by the detector, by constantly analysing the switching processes for the lighting in the room. This enables it to calculate the current daylight intensity at any time from the total measured brightness. The advantage of mixed light measurement is that it works with any light source – whether LEDs, halogen or fluorescent lamps. Mixed light measurement is the essential component of constant light control.

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Constant light control

With constant light measurement, the presence detector continuously measures the sum of daylight and artificial light. It determines the desired brightness value from these two light sources. On a misty or rainy morning the incident daylight is less. In this case, the presence detector increases the proportion of artificial light in order to reach the desired brightness in the room. If the sun breaks through in the course of the morning and there is more incident light through the windows, the presence detector reduces the proportion of artificial light. The brightness level in the room therefore remains constant, regardless of the incidence of daylight. Typical applications include production buildings where a specific brightness level is required by law.


Planning and installation

Correct installation of presence detectors

To ensure optimum functionality of the presence detector and to avoid sources of interference, a number of factors must be considered during installation. For example, there should be nothing obstructing the presence detectors field of vision, such as suspended lamps, partitions, shelves or large plants. Sudden temperature changes in the surroundings of the presence detector – for instance caused by switching fan heaters or fans on or off – simulate movement. Lamps which are switched on or off in the vicinity of the detection area (e.g. halogen lamps at a distance of less than 1 m) simulate movement and can lead to incorrect switching. Moving objects, such as machines and robots, simulate motion signals or temperature differences. However, slowly warming objects, such as heat radiators (lateral distance from lines and radiators greater than 0.5 m), IT equipment (computers, monitors), sunny surfaces, or room ventilation systems do not disturb the function of the presence detector as long as the warm air is notdirectly pointed at the presence detector.

Application examples for the ideal positioning of the presence detector in various rooms can be found here.

Planning security with sensNORM

As a member of the European association and quality label sensNORM, Theben and other industry representatives are committed to greater transparency, quality and planning certainty for motion and presence detectors in building automation. Products carrying the sensNORM quality label have been tested in line with standardised test specifications, allowing consumers to make a cross-brand comparison they can rely on.The measuring method according to sensNORM has established itself as an industrial standard and was included in the European standard IEC 63180. The measured detection areas according to sensNORM can be found in the data sheets of the respective products.

Free planning software for safe detector positioning

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Customers wishing to position, use and control the light correctly right from the start will benefit from Relux light simulation, which is generally free of charge. Relux offers professional planning software for development and implementation of complex lighting control tasks. The software for planners, architects and light designers is based on light-ing solutions from various manufacturers and is valued by its users around the globe. Theben is a Relux member in the sensors product group. More info at

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The RED CAD planning software can be used to create plans professionally and efficiently. Thanks to the integrated icon library with the proven Theben motion and presence detectors, the detection areas can be quickly and reliably included in the plans. More info at