Glossary · Machine vision
Backlighting
Also known as: Backlight illumination, Transmitted light
German: Hintergrundbeleuchtung
In machine vision, backlighting is an illumination technique in which the light source is placed behind the object, facing the camera, so the object appears as a dark silhouette against a bright background. It gives high-contrast edges for measurement and presence checks.
- Machine vision
In one sentence
Backlighting places the light behind the object, so the camera sees a sharp dark silhouette for measuring outlines and checking presence.
Example
With backlighting, the camera measures the diameter of turned pins to 0.02 mm because only their silhouette matters.
How it applies
- Engineering: Backlighting suits outline measurement, hole detection and inspecting transparent or translucent parts. Combined with a Telecentric lens and collimated light, it enables precise dimensional measurement. Diffuse backlights give even silhouettes; collimated backlights give sharper edges for gauging.
- Operation and maintenance: Dust or residue on the light surface appears as defects; cleaning intervals matter. Because only the outline matters, backlit inspections are largely insensitive to surface color and texture of the part.
- Documentation: The documentation team should document the lighting geometry with a sketch (light, object, camera), the light model and intensity, and cleaning instructions for the light surface.
Backlighting vs. front lighting
Backlighting shows only the outline; surface features are invisible. Front lighting such as Bright-field illumination or Dark-field illumination shows the surface.