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Basic knowledge illumination angle


Law of Reflection

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.

Illumination angle

The lighting setup should illustrate the approximate angle at which the light hits the D-SUB connector.


Incident light, direct

Direct incident light can be used when highly reflective surfaces need to be examined for embossments, hatchings, or less reflective colors.

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Incident light, angled

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, tilted

Dark field accentuate beveled edges and scratches while at the same time giving the flat surface within a depression a dark appearance.

Dark field, horizontal

The horizontal darkfield illumination is often used for position control. It creates a significant contrast between brightly illuminated edges and appearing black surfaces.

Back lilght

Transparency and backlighting can be used to illuminate thin materials, allowing for the detection of inclusions. Additionally, position control of opaque parts can be achieved effectively.

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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.

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