Machine Vision Lighting Guide
A working reference for engineers selecting lighting for inspection, measurement, and automation.
Geometry First
Geometry — front bright-field, dark-field ring, diffuse dome, backlight, coaxial — usually has more impact on image quality than wavelength or intensity. Pick geometry from the surface and the feature to enhance, then refine.
Wavelength & Color
Use monochrome illumination matched to camera sensitivity for measurement and OCR. Red (625nm) is a common default for contrast. Blue (470nm) suppresses IR contamination and enhances fine surface texture. UV is reserved for fluorescence applications.
Diffuse vs. Directional
Diffuse light (domes, flats) hides surface texture and is forgiving on curved/specular parts. Directional light (bars, low-angle rings) emphasizes texture, scratches, and edges. Most defect inspection needs directional light; most OCR/print verification needs diffuse light.
Strobing & Speed
Above ~1 m/s of part motion, strobe the lighting and gate the camera. Continuous overdrive can damage emitters; use IOO controllers rated for strobe duty cycles.
Environment
Washdown, high-temperature, and hazardous-location requirements constrain housing material, IP rating, and cabling. Specify environment up front — retrofits are expensive.
Common Failure Modes
Hotspots on specular parts, ambient light leakage, polarization-induced loss of contrast, IR drift from heat, and aging of inexpensive LEDs are the most common reasons a deployed inspection drifts. Plan ambient-light shielding and lighting service life from day one.