Coaxial light

Coaxial light (coaxial illumination) is used in machine vision systems to inspect flat, reflective surfaces where conventional lighting fails to provide stable contrast. By projecting light through a beam splitter along the optical axis of the camera, illumination and observation share the same path, causing specular reflections from flat areas to return directly into the lens. In practice, this results in a bright and uniform appearance of flat surfaces, while deviations such as scratches, etching, or contamination disrupt the reflection and become visible.

The effectiveness depends strongly on surface flatness and reflectivity; even small angular variations can redirect light away from the camera and create contrast. A common mistake is using coaxial light on curved or diffuse surfaces, where the coaxial effect breaks down and contrast is lost. The interaction between illumination, lens aperture, and viewing angle determines whether reflected light is captured efficiently by the sensor.

Coaxial light is widely used in electronics inspection, PCB inspection, and surface defect detection on polished materials. In combination with a suitable lens and sensor, it enables stable and repeatable contrast on uniform surfaces, where selection depends on field of view, working distance, and required defect sensitivity. Our LED coaxial light solutions are designed for industrial integration, offering high uniformity and stable optical alignment for reliable inspection performance.