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Infrared Machine Vision lighting

Infrared (IR) Machine Vision Lighting

Why use infrared imaging?

Infrared (IR) machine vision lighting enables vision systems to properly recognize an object and its condition under difficult lighting conditions; for example, reflective surfaces that produce high levels of visible-spectrum noise, excessive or extremely low levels of illumination or target areas with variable light intensities. IR has a longer wavelength than visible light so can transmit further into certain materials such as glass, semiconductor, paper, cloth and plastic. As a result, certain defects or flaws can be detected with IR which cannot be seen with visible light. 

IR Spectrum

Machine Vision System Considerations

When building an IR vision system, the correct combination of camera, lighting and software components must be considered.  For cameras, the speed of measurement, level of sensitivity and price are important factors when deciding on the optimum system configuration. The choice of illumination directly affects the choice of camera since different camera sensors have different optimum wavelength sensitivities.

In machine vision, most of the IR applications are located in the near infrared range, which comprises the spectral range from 780 to 3000 nm. NIR cameras for machine vision are primarily based on Silicon (Si) or Indium-Gallium-Arsenide (InGaAs) based sensors where Si is sensitive to light in the range of 400 to 1000 nm and InGaAs cameras are sensitive to light in the range of 900 to 1700 nm. 

Infrared Machine Vision Lighting Considerations

Designing any machine vision system is as much about managing trade-offs as it is about optimizing the systems performance at an acceptable cost.

The material under inspection determines the range of wavelengths that can be utilized as different materials absorb different wavelengths more easily. It is important to choose your wavelength correctly as even wavelengths a few nanometers apart can have wide variations in price and optical efficiency.

Once the wavelength or wavelengths have been selected, the overall scene to be illuminated needs to be examined to ensure the illumination solution captures the relevant information in the camera sensor. It is important to consider the size of the illumination area and understand what shadows and reflections will be present during the systems operation. The beam profile, the intensity, the working distance and the positioning of the illumination module are critical to producing the optimum illumination profile. Careful design of the LED layout, lenses and reflectors maximize the modules performance. All of these factors need to be considered while taking into account that there can be strict constraints on the modules form factor when integrating IR illumination modules into OEM systems.

IR illuminators operating at high intensities or located in constrained or enclosed spaces benefit for well-designed heat-sinking. Good thermal design will take the environment, IR LED packing density, specified run time, current drive rates, strobe flash, and correct heat-sink material into consideration to develop the proper solution ensuring the efficacy of the LED illuminator and longevity of the LED chips.

ProPhotonix specialize in developing custom IR LED solutions to maximize our customers’ system performances by focusing on wavelength precision, uniformity control, power management and miniaturization.