Glossary · Machine vision
Dark-field illumination
Also known as: Dark-field lighting, Low-angle lighting
German: Dunkelfeldbeleuchtung
In machine vision, dark-field illumination is a lighting arrangement in which light strikes the object at a low angle so that directly reflected light misses the camera; flat surfaces appear dark and features that scatter light, such as scratches, edges or embossing, appear bright.
- Machine vision
In one sentence
Dark-field illumination lights the object at a low angle so flat surfaces look dark and scratches, edges or embossing stand out bright.
Example
Dark-field illumination makes the dot-peened code on a steel part readable because the dots scatter light into the camera.
How it applies
- Engineering: Low-angle ring lights and bar lights create dark-field conditions. The method highlights surface texture, scratches, dust and embossed or engraved features. Dome and coaxial lights, by contrast, produce bright-field conditions and hide much of this texture.
- Commissioning: Working distance is critical because the light angle changes with height; parts must be presented at a consistent distance.
- Documentation: The documentation team should document light type, height and angle, and make clear to maintenance staff that moving the light changes the result.
Dark-field vs. bright-field illumination
In Bright-field illumination, directly reflected light enters the camera and flat surfaces look bright. In dark-field, only scattered light enters and flat surfaces look dark. The choice depends on which features need contrast.