Illumination for Machine Vision

On this page, you will find a comprehensive guide and an overview of key product groups in the field of illumination for machine vision.

 

Learn which lighting technology is suitable for your application, what you should look for when selecting and integrating it, and how different types of lighting (e.g., LED or diode lasers) can be systematically compared. The content will help you better understand technical requirements and find the right solution more quickly, regardless of whether you are just getting started or already have specific criteria in mind.

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Explore our Lighting Categories for Machine Vision Applications

Why the right illumination is essential for efficient machine vision?

 

In machine vision, image quality is not created by the sensor or optics alone - it starts with the light. Purpose-built machine vision lighting produces the necessary contrasts, make relevant features visible, and thus enable reliable, automated inspection and measurement. Non-uniform, insufficient, or misdirected lighting, on the other hand, leads to shadows, glare, increased noise, or incorrect measurement results.

 

A precisely coordinated light source is essential, especially in dynamic applications, such as line-scan or high-speed cameras area-scan imaging. The camera type, exposure strategy, wavelength, timing (strobe duration, duty cycle), and illumination geometry must be suitable for the application scenario in order to avoid image artifacts and process instability. Factors such as ambient light, mechanical constraints, and synchronization with trigger events are also crucial for overall performance.

 

In short, without optimized lighting, any vision system will fall short of its potential. Only with the right lighting solution can the hardware be turned into a robust, reproducible inspection or measurement system.

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Not sure which light source is right for your application? We can help you with selection and integration quickly, independent of manufacturers, and with a practical, application-driven approach.

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From light selection to system integration: We accompany you through all project phases and ensure a tailor-made, high-performance vision solution.

Guide to illumination for machine vision

In machine vision, the right lighting determines contrast, stability, and ultimately the quality of your image data. With the multitude of technologies, designs, and spectra, the question quickly arises: Which lighting is right for my project? This guide helps you make a systematic decision - even without in-depth prior knowledge.

1. LED or laser? The fundamental decision

The vast majority of applications today use LED - it is durable, efficient, compact, and available in many variants (ring lights, bars, panels, etc.). It suits reflected-light, transmitted-light, and dome concepts and supports fast, repeatable strobing.

 

Laser illumination comes into play where structured light (e.g., lines/spots/grids for 3D triangulation or profiling) is required or where very high light intensity is needed on a small area or at long working distances. Diode lasers are also increasingly being used in NIR inspection (e.g., sorting/inspection in the food industry).

 

Typical decision criteria:

  • Structured light or 3D measurement? → Laser
  • Area illumination, or uniform backlight? → LED
  • UV or IR range? → Both technologies are possible (choose by intensity, homogeneity, and safety needs)

 

 

2. Which geometry is suitable for the application?

The arrangement and shape of the lighting have a strong influence on image contrast:

  • Ring light (LED): Uniform incident brightfield. Ideal for flat objects with medium contrast requirements.
  • Bar light/line light: Versatile; can be used at grazing/low angle to emphasize texture and relief. For line-scan/web/track inspections, use focused line lights.
  • Coaxial light: Shadow-free bright field illumination using a beamsplitter. Perfect for reflective, flat surfaces; minimizes shadows and glare.
  • Dome lighting: Diffuse, uniform illumination. Very good for glossy or curved parts; suppresses glare and directional shadows.
  • Transmitted light / background light: Reveals contours and silhouettes. For measurements or presence checks.
  • Dark-field (low-angle): Highlights edges, burrs, scratches, and relief on otherwise low-contrast surfaces. 

Practical tip:

Choose geometry based on the feature of interest

  • edges/contours → backlight (telecentric for metrology)
  • surface finish/defects → low-angle or diffuse
  • flat specular → coaxial.

3. Which wavelength is best?

  • White light (broadband): Universally applicable; preferred with color cameras for neutral color rendering.Monochrome colors (red, blue, green): Ideal with monochrome cameras. Selecting a specific wavelength maximizes contrast via material absorption/reflectance.
  • UV (365–405 nm: Excites fluorescence and can reveal surface defects or microcracks.
  • NIR (740-1000nm): Useful for semi-transparent materials, reduces visible glare, improves contrast in food/organics.
  • SWIR (1000-1700nm): Enables contrast based on moisture/water absorption, inspection through some plastics, and silicon inspection (>1.1 µm).

Basic rule: With monochrome cameras, a narrow wavelength (plus matching filter) often yields maximum contrast. With color cameras, white light usually takes priority for neutral, faithful color.

4. Continuous light or flash?

  • Continuous light: Simple setup. For stationary or slow-moving objects, line scan with constant speed.
  • Flash (strobe): Short, high-intensity pulses to freeze motion and boost SNR.. Ideal for fast movement or when higher F-numbers are needed.


Note: Strobe lighting typically requires a separate controller or integrated control. Ensure synchronization with the camera trigger/encoder.

5. How bright does it need to be?

  • Is the light intensity sufficient for the desired exposure time and F-Number?
  • Is the scene uniformly illuminated (no hot spots, no shadows)?
  • Is there ambient light that needs to be suppressed or outshone?

Rule of thumb: Plan in headroom. It is better to have more light and then dim it than to run the camera at high gain (which raises noise) or struggle with too little illumination.

6. What are the prevailing environmental conditions?

  • Temperature, humidity, dust: Use industrial-grade lighting with the required IP rating and specified temperature range.
  • Vibration/shock: Rigid mounting, strain relief, and robust connectors (e.g., M12) improve reliability.
  • Installation space: Some geometries (e.g., domes, telecentric backlights) need clearance; allow for working distance, cable routing, and clear aperture.
  • Extraneous light/daylight: May need to be shielded or suppressed with enclosures, bandpass filters, polarization, and synchronized strobing.
  • EMC/EMI & cabling: Ensure proper grounding and controller placement; strobe currents can induce noise.
  • Safety: Observe eye-safety (laser/UV) and surface temperature limits.

Recommendation: Clarify the conditions at the installation site at an early stage. This will influence the design and control of the lighting.

7. Does the light harmonize with the camera and optics?

  • Does the wavelength match the sensor sensitivity (QE)?
  • Are filter, polarization, and light wavelength compatible?
  • Is the lighting mechanically and optically aligned with the camera/optics?

Tip: Coordinate the camera, optics, and lighting as one system. The best result is achieved with the right combination.

Do you need help with the design? Our experts are here to help!

 

Our experts will help you select the optimal lighting – tailored to your camera, lens, and application.

Frequently asked questions

What happens if I just use the ambient light?

Uncontrolled ambient light (daylight or hall lighting) is unstable in level and spectrum and can introduce flicker. It causes changing brightness, shadows, glare, and reflections. This leads to faulty or non-reproducible image data. Defined, homogeneous, and application-specific lighting is essential for reliable evaluation.

What lighting is suitable for shiny or reflective surfaces?

Coaxial/on-axis lighting is ideal for flat, specular surfaces; it delivers uniform bright-field illumination and controlled reflections along the optical axis. Dome (diffuse) lighting is best for curved or highly glossy parts; it suppresses hotspots. Polarizers (cross-polarization) can further reduce glare.

Which light source is suitable for high-speed inspections?

For fast processes, high-intensity flash lighting (strobe) with short pulse widths is usually used. This enables short exposure times and reduces motion blur. Precise synchronization with the camera is important here; observe controller limits for pulse current, duty cycle, and repetition rate.

What do I need to consider when integrating lighting into an existing system?

The following are essential: space requirements, mounting angle, power supply, controller comptability (continuous light or strobe inputs), and optical coordination with the camera and lens (clear aperture, working distance, geometry). The wavelength of the lighting should match the sensor spectrum, and mechanical stability and, if necessary, ingress protection (IP) classes must be taken into account.

Can I retrofit lighting if the image has too little contrast?

Yes –contrast  can often be improved with targeted changes. Often, small changes (e.g., wavelength selection, geometry/angle, using polarization, and bandpass filtering matched to the light source) are enough to make relevant features visible. STEMMER IMAGING provides support in selecting compatible retrofit solutions – even for existing systems.

How do I proceed in the case of strongly fluctuating ambient light (e.g., daylight)?

In environments with changing light – such as open facilities or near windows – ambient light should be outpowered by high-intensity and narrowband lighting. Enclosed dome or coaxial setups help block stray light. Avoid automatic exposure adjustment on the camera, as it may react unpredictably to such fluctuations; use fixed exposure/gain.

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