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Best Practices for Light Control

Why is controlled light so critical when applying vision systems? Light is the most critical tool for creating adequate contrast for a successful and reliable machine vision application. Quite simply contrast is the delta between the light levels on the feature(s) of image, and every other feature visible to the imager--the background. The total scope of the area seen by the imager, or field-of-view, is divided between the feature(s) of interest, and the background of these featured. Illumination of the feature(s), or conversely the background of the features when they are darkened, is the heart of a successful application. Choices for lights to create and amplify contrast are nearly infinite. Lights are available in differing photon producers---Halogen, incandescent, LED, . . .---differing shapes---spot, area, linear, collimated, diffused, co-axial, . . . and differing colors or wavelengths. To cut through the cacophony of options---a quick method to simplify is if you can backlight the application, do it. Backlighting---or placing a light(s) opposite the smart camera maximizes contrast. Backlighting creates a silhouette. Opaque objects are dark---and more translucent or empty air space in the rest of the field-of-view are contrastingly bright. Often backlighting is not feasible---the mechanical space to fit the part between the camera and light is unavailable. Or the feature(s)-of interest are on the surface of an opaque background. Thus the “art” of optimal lighting for creating contrast quickly becomes more complex. Once the lighting method is determined a critical practice is to make controlled light immune from “light pollution.” The best ways to eliminate ambient light from affecting robust contrast are: 1. Mechanically shroud the part being inspected and its lighting---build a chamber isolating the application from outside light. 2. Use high-powered lights for the application. Create enough photons and shadows that the ambient lights have no effect on the application’s contrast. 3. Use infrared light and filters to optically shield the application from visible light. Learn more about creating contrast using machine vision lighting on pptvision.com