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Guides
Most lighting guides stop at angles and colors. These are the effects that catch experienced teams after the station is already running.
Our lighting and optics guide covers where to put the light. This page covers what the light does once it is there: how its spread, its color, its temperature and the way it is dimmed change the picture, sometimes enough to move a measurement or fail good product.
Light from a diffuse panel leaves at many angles. Some of it wraps around the curved edge of a pin, needle or tube and eats into the silhouette, so the part measures undersize. A collimated backlight, where the light travels parallel, keeps the edge where it really is. Use it for gauging round parts.
Light spreads a little as it passes an edge, and shorter wavelengths spread less. Switching a gauging backlight from red to blue can tighten the edge without changing the camera or lens.
Red and amber LEDs lose noticeably more output with heat than blue ones. A brightness or color check taught on a cold light can drift by midday. Strobing keeps the LEDs cool, and a warm-up before teaching avoids the drift.
A white LED is a blue chip under a yellow coating, with a dip in the blue-green range between them. Teal and blue-green features can look flat or shifted under it. Test color checks on the real light before trusting them.
Many controllers dim by switching the LED on and off very fast. A rolling-shutter camera reads the sensor line by line, so it catches that flicker as bright and dark bands that move from frame to frame. Dim with current, or strobe the light in step with the exposure.
A polarizer on the light and a second one on the lens, turned at right angles, cancels the mirror-like glare on foil, film and wet product while keeping the print visible.
Every one of these can be tested on the bench in an afternoon with real samples. Test before the station ships, not after the first complaint.
FAQ
No. It matters most for round or thick parts where light can wrap around the edge. Flat, thin parts measure well on a diffuse backlight.
No. Short pulses keep the LEDs cooler than running them all the time, so they usually last longer and drift less.
Your eye adjusts for flicker, color and brightness. The camera does not. What looks steady to you can change frame to frame for the sensor.
Often a monochrome camera with the right colored light is more stable. A color camera is needed when the check has to tell many colors apart.
