Eliminating Reflections & Glare with Polarized Lighting

The Physical Problem

Metallic, glass and wet surfaces reflect a large fraction of incident light specularly, in a narrow, mirror-like cone. When that reflection points straight into the camera's lens, it clips the sensor at those pixels — the region reads as pure white regardless of what feature, defect or code sits underneath the glare. Because a clipped pixel carries no information, no amount of re-exposing, re-gaining or re-processing the image afterward can recover what the sensor never actually measured; the only fix has to happen at the light itself, before the reflection ever reaches the lens.

The Optical Solution

Unpolarized light reflecting specularly off a non-metallic surface becomes partially linearly polarized in the process — a real, well-established property of dielectric reflection. Light scattered diffusely from beneath the surface or from a rougher matte area, by contrast, keeps a much more random mix of polarization states. Placing a linear polarizing filter on the light source, and a second linear polarizing filter on the camera lens rotated 90° relative to the first — a "crossed" configuration — blocks most of that specularly polarized glare while still passing a large share of the depolarized diffuse light. The saturated hot spot disappears, and the feature that was hiding underneath it becomes visible.

Integration Tools

• M12 5-Pin Wiring Diagram