Inspection lighting: backlight, ring, dome or strobe?

Start with the feature that must become visible

Lighting must create sufficient contrast on the inspected feature across the permitted product and position variation. Start by testing the part, viewing direction and available installation space.

Backlight

Backlight reveals silhouettes, outer edges, missing material and through-holes. It suits inspections where shape matters more than surface texture. Transparent material may require additional trials because of refraction.

Ring light

A ring light illuminates the surface from several directions around the lens. It suits presence checks, simple print and surfaces with limited reflectivity. Glossy film or metal may produce bright reflection spots.

Dome light

A dome distributes light across a wide range of angles. It can reduce reflections on curved or glossy parts and is therefore useful for cosmetic and print inspection. Allow for the required installation volume.

Strobe

A short light pulse helps freeze motion during exposure. Coordinate pulse duration, exposure time and trigger. Verify the thermal load and maximum repetition rate of the selected light.

Practical test

Capture good parts, defective parts and borderline cases at minimum, nominal and maximum line speed. Compare contrast, reflections, motion blur and sensitivity to position variation. The broader selection method is covered on the machine vision lighting page; products are listed under Lighting.