The Vision That Couldn’t See: Lighting, Not Camera Resolution
A vision system reading a laser-etched code on a shiny metal part. The camera couldn’t read the code — the image was washed out by reflections. We increased the exposure. Worse. We changed the lens. No improvement. The problem was the lighting, not the camera.
The reflection problem
A shiny metal surface reflects light. If the light source is in the wrong position, the reflection goes straight into the camera. The image is overexposed (white). The dark code is lost in the glare. No amount of camera adjustment fixes a reflection problem.
The lighting options
| Lighting type | How it works | Best for |
|---|---|---|
| Coaxial light | Light along the camera axis, half-mirror | Shiny surfaces, flat parts |
| Dark field (low angle) | Light at a grazing angle | Etched codes, scratches |
| Diffuse dome light | Omnidirectional, no direct reflection | Curved shiny parts |
| Back light | Light from behind the part | Silhouette, outlines |
| Direct ring light | Ring around the lens | Matte surfaces (not shiny) |
What we used
We switched from a direct ring light to a dark-field light (low-angle, 15° from the surface). The light hits the shiny surface at a grazing angle. The flat surface reflects the light away from the camera. The etched code (which has rough walls) scatters light back to the camera. The code appears dark on a bright background. The camera reads it perfectly.
The coaxial alternative
For a flat, shiny surface (like a machined plate), a coaxial light works. The light goes through a half-mirror, along the camera axis, and reflects straight back to the camera. The flat surface returns the light uniformly. Any defect (etched code, scratch) scatters light differently. The camera sees the contrast. But coaxial lights are expensive ($500+). The dark-field light ($150) solved our problem.
The camera settings
After the lighting was correct, we adjusted the camera: gain low (no digital noise), exposure 5 ms, aperture f/8 (deep depth of field). The image was sharp. The code contrast was 3:1. The vision software read 100% of codes. The camera was fine all along — it just needed the right light.
The vision lighting rule: If the camera can’t read a shiny part, the lighting is wrong. Use dark-field for etched codes, coaxial for flat shiny surfaces, diffuse dome for curved parts. Don’t increase exposure to fight reflection — it makes it worse. The light determines the image; the camera just captures it.
