The Vision That Couldn’t See (Bad Light)
We used a vision system (a camera) to inspect a part (find the part’s position). On the bench (dim light), it worked (the camera saw the part). On the floor (bright plant light, windows), it failed (the camera couldn’t see — glare from the sunlight). The problem: the lighting. The camera (without a controlled light) sees the plant’s light (glare, shadows). We added a controlled light (a ring light, article 193). The ring light illuminates the part (even, no glare). The camera sees the part (against the dark background). The inspection worked. The mistake was not controlling the light (the camera saw the plant’s light, not the part).
Vision lighting controls the light (for the camera). This article covers the basics.
The Light Sources
- Ring light: A ring (around the lens). Even light (for a flat part). General inspection. No glare (if diffused).
- Back light: Light from behind (the part is a silhouette). For measuring the part’s outline (no detail, just the shape). Sharp edge (good for gauging).
- Coaxial light: Light along the lens axis (for a reflective surface, a shiny part). No glare (the light is diffuse).
- Bar light: A bar (for a long part). Even (along the length).
Step 1: The Part (Reflective?)
A shiny part (metal, reflective) needs a diffuse light (a coaxial, or a diffused ring). A direct light creates glare (the reflection). A diffuse light (soft, even) illuminates the part (no glare). A matte part (plastic) is fine with a direct ring.
The vision lighting rule: Control the light (don’t rely on the plant). The vision that failed had no controlled light (glare from windows). Add a ring (or back) light. The camera sees the part (against the dark background). Shut out the ambient (a hood, or a shield).
Step 2: The Contrast
The camera sees contrast (the part vs the background). A light part on a dark background (or vice versa). For a dark part, use a bright back light (the part is a dark silhouette on a bright background). For a light part, use a dark background (the part is bright on dark). Maximize the contrast.
Step 3: Shut Out the Ambient
The plant’s light (windows, overhead) interferes. Add a hood (a shield over the camera) — the camera sees only the controlled light (not the ambient). The hood blocks the sunlight (glare). For a part on a conveyor, the hood covers the camera (and the part).
Step 4: The Color (Wavelength)
Use a light color (wavelength) that contrasts. A red light (for a blue part) absorbs (the part is dark). A white light (general). For a special part, use a matched color (e.g., infrared, for a feature).
| Part | Light |
|---|---|
| Flat (matte) | Ring light |
| Outline (gauging) | Back light |
| Shiny (reflective) | Coaxial (diffuse) |
| Long (shaft) | Bar light |
A Vision Lighting Checklist
- Is the part reflective? (Needs diffuse?)
- Is the contrast right? (Part vs background?)
- Is there a controlled light? (Ring/back?)
- Is the ambient shut out? (Hood?)
- Is the color matched? (Contrast?)
- Does the camera see the part? (Test?)
- Is the glare gone? (Sunlight?)
- Is the focus right? (Lens?)
- Is the trigger right? (Part present?)
- Is the inspection consistent? (Repeats?)
The Bottom Line
Vision lighting controls the light. The vision that failed had no controlled light (glare). Add a ring (or back) light. Shut out the ambient (hood). Maximize contrast. The vision that saw the part wasn’t the best camera — it had the right light.
