Advanced Imaging

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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Lights! Camera! Action!

Illumination better come first when planning machine vision system
microscopic illumination
© Courtesy Volpi
Illumination is one of the most crucial aspects of any application. New users need to allot plenty of planning time.
lighting equipment
© Courtesy Mercron
Engineers have to make sure of the details. Figuring out lighting needs is one of their most difficult tasks.
Monster backlight from Spectrum
© Courtesy Spectrum Illumination
Pick the proper lighting before getting too far into the project. This is a Monster backlight from Spectrum.
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By Barry Hochfelder

LED lighting is the fastest growing because there's been such a huge increase in intensity, especially white, says Muyskens. "It has doubled in intensity from a year ago. The home market is trying to replace standard incandescent bulbs, and that's why white is advancing so much. You won't see it that fast with other colors. It's gone from 45 lumens to 90 lumens just that fast, but you can drive it to over 200 lumens per LED.

"Advances in LED [combine with] the disadvantages of halogen or fluorescent or xenon strobes, [which] have such a short lifespan. LEDs have made huge advances; they're getting closer and closer to where they can compete with the brightest. I have some projects switching from xenon strobe to LED because the brightness is getting so close."

Most LED users require a driver, or controller around each light source. LED current controllers typically provide a digitally controlled, repeatable constant current output, along with accurate pulse timing with variable delay and pulse width and selectable intensity. Current and pulse timing are set manually or dynamically from software and are stored in the controller, explains Peter Bhagat of Gardasoft Vision in the U.K.

The pulses are triggered on an opto-isolated digital input, usually from a PLC, frame grabber or camera. The pulse width and the delay before it fires can be controlled. "Often two or more views of an object are taken using different lights at different intensities," Bhagat says. "With an LED lighting current controller it is possible to switch lights on and off and to switch between several preset intensities."



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