Machine vision lighting is application-specific: the wrong lighting geometry makes a great camera and lens produce unusable images, while the right lighting makes inspection problems look easy. Selection depends on the target surface, the defect to be highlighted, and the required cycle time.
Lighting geometry by application:
- Ring light: coaxial illumination from around the lens — general inspection, label-presence verification, OCR/OCV. Easy to set up, produces hot spots on shiny surfaces
- Bar light: linear illumination from one or both sides — line-scan inspection, web inspection, raking light for surface defects
- Dome light: diffuse hemispherical illumination — shiny and curved surfaces (cans, bottles, painted parts) where hot spots must be eliminated
- Backlight: illuminated panel behind the part — transparent inspection, silhouette and edge detection, dimensional measurement
- Low-angle (dark-field): light grazing the surface at a shallow angle — surface defects (scratches, dents, embossing) that reflect light off-axis
- Coaxial / on-axis: light directed along the optical axis through a beam-splitter — mirror surfaces, foiled labels
- Structured pattern: projected line or grid pattern — 3D profile inspection, height measurement
Other specs:
- LED color: red (deep penetration on certain materials), white (color inspection), blue (high contrast on red marks), IR (covert detection, hot-object imaging), UV (fluorescence)
- Strobe vs. continuous — strobe extends LED life and reduces motion blur on fast lines
- LED controller — constant-current driver matched to the LED specification
- Trigger input from camera or PLC (typically 5 V or 24 V pulse)
- Cooling — high-power LED lights run hot and need adequate convection
Common gotchas: a bright LED light run continuously at full output overheats and degrades quickly; the same light strobed gets brighter peak output AND longer lifetime. LED color choice matters more than expected — a blue defect on red background pops with red illumination and disappears under white. Dome lights eliminate hot spots but lose much of their brightness through the diffuser; budget for higher-power versions than equivalent ring lights. Light controllers and lights are usually a matched pair — substituting either alone changes the LED drive current and the resulting brightness/color.
Typical applications: label presence verification (ring), web defect detection (bar with rake light), bottle inspection (dome), bag inspection for fill level (backlight), surface defect detection on machined parts (low-angle), and 2D code reading on shiny stainless (coaxial).
For obsolete machine vision lighting, send the OEM part number for a sourcing quote.
