The main task of lighting is to create the best possible contrast difference between the defect feature and the component. The lighting angle and form have a decisive influence on how the inspection and defect features become visible in the image.
The fundamental rule in the arrangement of lighting is the law of reflection:
Angle of incidence = Angle of reflection
Depending on the surface structure, material composition, and shape, the light can be directed from above, angled from one side or both sides, horizontally directed, or directed from underneath onto the test object. The light is reflected, scattered, absorbed, transmitted, or a shadow is cast on the test object and its defect features. In addition to the lighting angle, it is important whether the light strikes the test object directly or diffusely. The same object leads to a completely different result in the camera image depending on the positioning of the light.
Direct incident light can be used when highly reflective surfaces need to be examined for embossments, hatchings, or less reflective colors.
Similar to direct incident light, angled incident light is highly suited for inspecting surface textures. The slight tilt of the LEDs highlights edges better and shadows are created in depressions.
Dark field accentuate beveled edges and scratches while at the same time giving the flat surface within a depression a dark appearance.
Coaxial lighting provides a homogeneous illumination of highly reflective surfaces and, thanks to the internally built-in one-sided translucent mirror, creates an illumination without camera hole.
The dome light manages to illuminate uneven structures, thereby eliminating height differences. Additionally, glossy surfaces appear less shiny when exposed to indirect and extremely diffuse light compared to direct lighting.