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Luminescence Sensors FAQ

What is luminescence? How do luminescence sensors work? Where are these sensors used? This page answers frequently asked questions about the luminescence sensors. 

Luminescence refers to the illumination of luminescent materials under UV light.

A luminescence sensor lights a fluorescent substance with invisible UV light (wavelength below 380 nm). The luminophores in the substance are activated by this and reflect visible light in the wavelength range of 420 to 780 nm. The luminescence sensor detects the reflected light and evaluates it.

Luminescence sensors are used to detect fluorescent markings on various objects and substances that are invisible to the human eye and other sensors. Markings on food cans can be detected, for example. Other possible uses include detecting chalk on marked knotholes in the woodworking industry, scanning labels on pharmaceutical products or aligning objects without optically visible markings.

Luminescence sensors detect luminescent markings on almost all materials. Natural luminophores, for example, are found in white paper, which glows blue when exposed to UV light. For materials that do not contain luminophores – such as glue, plastic, paint, ink, fluorescent chalk, cleaning agents and oil – they can be added artificially. These luminescent materials are not visible to the human eye.

Since luminescence sensors detect both visible and invisible luminescent markings, they are particularly suitable for use in products where the design must be free from markings.

The standardized IO-Link communication technology enables sensors to be connected to an automation system. The IO-Link interface for the luminescence sensors offers the following advantages:

  • Easy configuration of parameters and output of intensity values
  • Operation of condition monitoring or setting and setting of on/off delays

wenglor’s luminescence sensors reliably detect luminescent markings in the event of slight differences in color and contrast, as well as bright ambient lighting.

The luminescence sensors from the P1PA series differ with regard to the receiving range and the receiver filter. The P1PA001 luminescence sensor receives light that is emitted in the wavelength range of 420 to 750 nm and features a blue-permeable receiver filter. The P1PA002 sensor detects luminescent markings that emit light in the wavelength range from 570 to 750 nm and is used on surfaces luminescing in yellow-green.

Luminophores are substances that emit light after they have been exposed to short-wave light. This phenomenon occurs in fluorescence and phosphorescence. With fluorescence, luminophores only light up when they are exposed to the light. Fluorescent tubes use this principle, for example. Luminophores, which remain lit for a time after exposure due to phosphorescence, are used in the production of safety signs, for example.

There are three types of luminescence: Fluorescence, phosphorescence and bioluminescence. If the light is emitted immediately after the luminescent medium is activated, this is referred to as fluorescence. This phenomenon can be seen with black light. Phosphorescence occurs when the energy is held by the activated object for a certain time. Dials on watches or star stickers for the ceiling in a child’s rooms glow in the dark and contain phosphorescent materials. Bioluminescence describes the generation of light by living creatures, such as fireflies or marine phosphorescence by algae or plankton.

We can distinguish between three wavelength ranges: infrared light, visible light and ultraviolet light. Infrared light is present at a wavelength above 780 nm and is also referred to as thermal radiation. The light visible to the human eye is in the wavelength range from 380 to 780 nm. For wavelengths below 380 nm, ultraviolet light is used. Like ultraviolet light, infrared light is not visible to the human eye.

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