Inspection lighting is different from general illumination because the objective is not simply to make an area bright. The lighting must make the feature being inspected distinguishable from its surroundings.
That may require emphasizing an edge, flattening reflections, revealing scratches, creating a silhouette, highlighting surface texture, separating colors, or producing consistent illumination for a camera.
Image Quality
Inspection Depends on Contrast
Cameras and operators identify features when those features differ visibly from the background. Increasing total light output does not necessarily increase useful contrast.
The angle, direction, color, polarization, diffusion, and geometry of the illumination may have greater influence than raw intensity.
Illumination Geometry
Lighting Angle Changes What the Camera Sees
Front lighting can illuminate visible surfaces, while lower-angle illumination may emphasize surface irregularities or edges. Backlighting can produce a high-contrast silhouette around an object's profile.
Ring-shaped illumination can surround the optical axis, while bar and linear lights can provide directional illumination from selected positions.
The most useful geometry depends on the feature being inspected, the material surface, and the camera position.
Reflective Parts
Managing Specular Reflection
Polished metals, glass, plastics, coatings, and wet surfaces can reflect concentrated light back toward the camera and create bright glare.
Diffusers can enlarge the apparent source and soften directional reflection. Changing fixture angle or using a larger illuminated surface can also alter the reflection pattern.
Reflectors & Diffusers →Automated Inspection
Lighting for Machine Vision Systems
Industrial machine vision systems depend on repeatable images. If illumination changes from one part to the next, image-analysis performance can change even when the product itself has not changed.
Related optical inspection systems demonstrate why lighting, optics, cameras, positioning, and software should be treated as connected parts of the same inspection process.
Mechanical mounting should keep the light stable relative to the camera and target while shielding the inspection area from uncontrolled ambient variation when necessary.
Optical Control
Lenses, Diffusers and Filters
Optical components can adjust both distribution and spectral content. Lenses shape the beam, diffusers spread light, and filters can transmit selected portions of the available spectrum.
Optical windows may also protect the emitter and internal components from the inspection environment.
Strobing & Control
Synchronizing Lighting With Inspection
Some automated inspection systems control the illumination in coordination with image capture. Lighting can be switched or pulsed according to the machine sequence where the electronic design supports that operating method.
Driver electronics, control signals, LED current, thermal conditions, and timing should be designed as a coordinated system rather than assuming any LED assembly can be operated in the same way.
Electronics & Controls →Color
Spectral Selection for Inspection
Different materials and surface features can respond differently to illumination wavelength. Selecting a particular spectral region can change the visual separation between a feature and its background.
Applications involving color measurement have different requirements from applications where monochrome contrast is the main objective.
Design Review