Passive Infrared (PIR): 
Infrared Systems For Detecting Heat radiated from the Body

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There isn’t a right or a wrong Passive Infrared technology, there’s just the option that suits a specific lighting situation. The solution you choose all depends on what you want it to do.

PIR sensors in theory

Infrared sensors receive heat radiated from the human body. Segment lenses divide the detection zone into passive and active zones. This way, the highly sensitive sensors can detect persons or warm objects moving between the zones as a change in voltage. Even the smallest of movements are registered. The quality is governed by resolution (number of detection zones), design and the software.

PIR sensors in practice

Movements at right angles to the sensor (tangential movement) can be detected particularly well by passive infrared sensors. With radial movements, reach is usually shortened because detecting a change in temperature in this walking direction is more difficult. The point at which sensors are positioned should ensure they are not disturbed or distracted by

PIR sensors from STEINEL Professional

While developing our IR systems, we pay attention to precision and reliability, we pay attention to precision and reliability. Technological advances, such as multi-lens and multi-sensor technology, permit tremendous accuracy in reach settings and detection spectrum. Working with an exceptionally high number of switching zones, our IR Technology ensures sensors ensure precision and reliability. 

What are infrared rays?

Any object with a temperature that lies above absolute zero (- 273° C), gives offelectromagnetic radiation. Heat radiation is well suited as automatic remote control.

How does a PIR motion detector work?

The surrounding heat radiation is grouped by a segment lens and guided to the pyro-detector.If a heat source moves in the detection area, the heat radiation changes and thepyrosensor releases a voltage. This voltage is assessed by the downstream electronics.

Benefits of PIR

  • Very good tangential detection
  • Detection reach and angle of coverage can be set with precision
  • High number of switching zones
  • Also suitable for outdoors as only heat radiation is detected
  • Twilight threshold and light ‘ON’ duration and detection zone can be set to suit individual needs
  • Electronic temperature compensation to avoid differences between winter and summer detection quality outdoors


  • Light for seeing – for optimum illumination
  • Light to be seen – that creates highlights
  • Light to see – as decorative element
  • Light for saving – for energy-conscious illumination
  • Light for safety – as deterrence


The detectors automatically switch the light depending on the respective environment brightness and presence of persons. The passive infrared technology makes this possible, i.e. built-in IR sensors record thermal radiation and convert the same to a measurable electric signal. Bodies, such as the human body, emit thermal radiation; such thermal radiation lies within the so-called infrared range and is invisible to the human eye.

The heart of passive infrared (PIR) sensor technology is the lens. As the “eyes” of the sensor, it collects the infrared energy data generated by matter in space. Moving energy sources, such as humans, will emit radiant heat that is then collected by the lens. These data are passed to the sensor circuitry for interpretation; based on this, a signal is transmitted to switch lighting in the area. Because appropriate signals depend on the collection of comprehensive and accurate data, the quality and design of the lens is critical.

Fresnel Lens Technology

The lens technology most commonly used in passive infrared occupancy sensors today is based on the Fresnel principle, which is that the contour of the refracting surface of a lens defines its focusing properties. A non-spherical surface contour (also referred to as “aspheric”) will minimize optical aberrations and refract a higher percentage of the light energy being collected in the desired direction. This aspheric surface consists of grooves that can be varied in depth and thickness.

Advanced Lens Technology

While Fresnel lens technology is the foundation for the lenses used in The STEINEL PIR sensors, there are important differences between common Fresnel lens and the advanced types found in our products. Most importantly, Steinel utilizes lenses that have been specifically developed for use in our sensors.

Structure of a Fresnel lens

Combination of single lenses,arranged in a circular segmentMaximum horizontalangle of coverage of 180° with a Sneak-by protection:STEINEL Fresnel lenses havea second optical window underthe main detection zone. The radiation under the sensoris therefore also detected.

This involves an exclusive specification and lens design process, during which a prototype lens is crafted by hand and tested for effectiveness. Once the lens has passed this rigorous testing stage, the manufacturing process can begin, utilizing advanced plastics materials to customize lenses with excellent infrared optical properties. This process is applied for each sensor product to ensure that the specific capabilities intended for each sensor type are obtained.

Another significant difference between Steinel patented lenses and common Fresnel lenses is the use of multiple lens segments and tiers. This unique design is accomplished by identifying and selecting specific segments or “cells” of a common Fresnel lens design that have exceptional optical properties for a specific range. These cells are then pieced together with other segments. The effect, rather like a patchwork quilt, is illustrated in the [image below], which represents a lens surface. Lastly, these segments are arranged in levels, or tiers, to achieve multi-dimensional coverage.

Experts in the field of optics have developed different designs or patterns, each of which is protected by its own patent, to provide different coverage capabilities.



For further information please contact:

  • Pammvi Group of Companies
  • Mumbai
  • India

Website:  For More Info Visit To Our Site

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Infrared Systems For Detecting Heat radiated from the Body

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