Machine vision lighting: techniques by material
Choose the right lighting technique based on material property or inspection challenge.
This machine vision lighting reference helps choose the right illumination technique for industrial image inspection, based on material properties such as glossiness, transparency, texture and color. It covers dark-field lighting for glossy and reflective surfaces such as metal and glass, bright-field diffuse lighting (ring or dome light) for matte surfaces, backlighting for transparent and translucent objects, grazing (low-angle) light for revealing texture, scratches and dents, spectral testing with white, UV and infrared light for color differences invisible under white light, cross-polarization to suppress glare on glossy surfaces, and pulsed/strobed lighting for moving objects prone to motion blur.
Pick a row based on the material property or the problem you are trying to solve. Each diagram shows the general layout of camera, light source and object.
Glossy/reflective (metal, glass)
Dark-field, or coaxial with diffuser
On glossy surfaces, direct light bounces straight into the camera and overexposes the image, while surface irregularities stay dark. Dark-field lighting illuminates the object at a steep angle so the smooth surface reflects light away from the camera, while scratches and edges scatter light back toward it and appear bright. Coaxial lighting with a diffuser works on the same principle for smaller, highly reflective parts.
Matte/diffuse surface
Bright-field diffuse (ring or dome light)
Matte surfaces scatter light in all directions, so uniform diffuse lighting from the front is usually enough. A ring light or dome light around the lens provides even illumination without hard shadows or hotspots, giving consistent contrast for color and shape recognition.
Transparent/translucent
Backlight (contour) or diffuse transmitted light
Front lighting gives little contrast on transparent or translucent objects. Backlighting the object produces a sharp silhouette, ideal for contour and dimensional measurement; diffuse transmitted light instead reveals internal structures, inclusions or density variations within the material.
Texture/height variation, scratches, dents
Grazing light (low angle, ~10-15°)
Surface relief such as scratches, dents or texture is barely visible under perpendicular lighting, since it produces little shadow contrast. Skimming light across the surface at a very low angle (roughly 10-15°) causes even small height differences to cast long shadows, greatly exaggerating the visible relief.
Color variation/stains not visible in white light
Spectral test (white, UV 365-395nm, IR)
Some material differences — such as chemical contamination, moisture stains or material transitions — are barely visible under normal white light but show up under a different wavelength. Test with UV light (365-395nm), which can trigger fluorescence, and infrared light, which penetrates some materials more deeply or is absorbed differently by others. Log results per wavelength to determine which light source discriminates best.
Glare on glossy surface despite correct angle
Cross-polarization (polarizer on light + rotatable analyzer on lens, 90° crossed)
When dark-field or grazing light alone isn't enough to suppress direct glare (specular reflection), place a polarizing filter in front of the light source and a second, rotatable polarizer (analyzer) in front of the lens. Rotating the analyzer 90° relative to the first polarizer (crossed polarization) blocks polarized specular reflection while largely passing the diffusely scattered light from the object — the result is a near glare-free image.
Moving object (blur-sensitive)
Pulsed/strobed lighting instead of continuous
At high product speeds, the required exposure time is often too short for continuous lighting to deliver enough light. Driving the light source in pulsed (strobed) mode, synchronized with the camera trigger, delivers a high peak intensity during a very brief flash — effectively "freezing" motion without increasing the average exposure time. See also the shutter-time calculation in the Optics Calculator.
Spectrum test log
Track how different light sources/wavelengths perform on your material. Data stays local in your browser and is never sent to our server.
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