Measurement Selection

Backlight vs Coaxial Lighting for Measurement

Use a backlight when the camera needs a silhouette: outer profile, holes, gaps, and edges. Use coaxial light when the feature is on a flat face and the light must return along the lens axis. A backlight does not show a surface scratch, while coaxial light does not draw a silhouette outline.

Discuss Measurement Lighting Calculate FOV & Working Distance

Machine vision backlight panels for dimensional measurement — Backlight panels for silhouette, edge, hole, gap, and outer-contour measurement.

LuxMV machining area with CNC equipment — Reference 01Machining area for lighting housings.Send the part or the images with this condition.

Selection considerations

Open the matching series, then send the part or the images.

When should you use backlight vs coaxial illumination?

**Use backlights to measure physical geometry and coaxial lighting to inspect planar surface defects.** Backlighting is the optimal choice for outer profile, hole, edge, gap, and silhouette contrast. Coaxial lighting is mandatory for flat reflective marks or face features that need light returned toward the camera axis.

Lighting Type	Primary Use Case	Best For	Typical Defects Found
Backlight	Silhouette / Profiling	Opaque/Transparent Edges	Burrs, missing material, dimensional errors
Coaxial	On-Axis Reflection	Flat Specular Surfaces	Scratches on glass, QR codes on metal

What are the key parameters for selecting a backlight?

The backlight should be larger than the field of view so the edge of the lamp is not part of the measurement. Record the silhouette, the edge tolerance, the object-to-light distance, and whether a telecentric lens is required. There must be room for the lamp behind the object.

Technical considerations

Transparent or translucent behavior, burrs, and multilayer edge response.

What are the critical inputs for coaxial lighting specification?

Coaxial light is for a face that looks back at the lens. A slope or curve sends the reflected beam away from the camera, so the face goes dark. Check the actual curvature, the optical aperture, the field of view, and the working distance before treating coaxial light as the setup.

Technical considerations

Evaluate whether curvature, height variation, or texture makes on-axis reflection unstable.

Questions for the engineering discussion.

Can backlight inspect surface scratches?

Usually not as the primary method. Backlight is intended for silhouette and edge information; surface scratches often need directional, low-angle, coaxial, diffuse, or polarized tests.

Can coaxial lighting replace a backlight for dimensional measurement?

Not when the measurement depends on a clean silhouette or edge. Coaxial light may help planar face features, but it does not create the same object-versus-background outline as a backlight.

When should I use collimated backlights?

Use collimated backlights when inspecting thick transparent materials or highly precise cylindrical edges where standard diffuse backlighting would create wrap-around light and blur the true dimensional boundary.