By Stuart W. Singer and Jim Sullivan, Schneider Optics, Inc.
The human eye can only see, approximately, wavelengths between 0.400 μm (blue) and 0.700 μm (red). All those wavelengths combined appear to us to be white light, such as the natural light we see outdoors. Most, if not all, commercial off-the-shelf lenses are optically designed to create a high-quality image using white light.
However, while machine vision light sources exist that can create close-to-nature white light, many users do not use white light sources in their applications. As a result, digital camera-based vison system users can experience problems related to the responsivity of digital sensors to discrete wavelengths, including those produced by lasers and LEDs. A critical element of avoiding such issues is properly defining lighting requirements early in systems engineering when designing a vision system. Just as important, if white light is not being employed in the application, system designers and end users should understand the problems they might encounter, as well as how to identify and resolve those problems before the impact on their imagery is too late to correct.