Lighting tricks with wavelength

You know that lighting is the single most important part of any machine vision application. You also know that it makes sense to use LED lighting, thanks to the long life and relatively stable output, But how much thought do you give to the wavelength?

There’s no law that says you have to use light at 660 nanometers (a.k.a. “red light.”) In fact sometimes there are advantages from going out into the UV and IR regions of the spectrum, as discussed by Brent Evanger of Banner Engineering, in “Lights, Camera and Special Effects,” (Vision & Sensors magazine, November 30th, 2009.)

Brent gives a good summary of the benefits, although he does miss one point. In discussing the use of UV lighting, he covers only its use as a means of exciting visible wavelength fluorescence in the subject part. As some materials are naturally fluorescent that can be a neat way of doing presence/absence tricks, but there is another use too.

A consequence of the short wavelength is that diffraction effects are reduced. This means that if you need to do high precision gauging, and every pixel counts, UV light rather than red will give you a small but significant advantage.

But back to the magazine article … after exploring the value of wavelength, Brent also covers polarization. Now this is a really interesting topic because polarization, if properly understood and applied, can be a very powerful tool for solving “impossible” lighting problems.

I’m not going to steal Brent’s thunder by telling all here: use the link and read the source material: “Lights, Camera and Special Effects.”