Advanced Imaging


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.

By Barry Hochfelder

One way to avoid that error is to pick the right lighting as early as possible, says Dave Muyskens, President of Spectrum Illumination. "If they don't have the room later, it's hard to compensate for poor lighting. The earlier you can get involved in a project, the better. The design stage is better than trying to fit it in later."

Elements to consider: correct type, whether indirect or dark-field illumination or backlight. Most people know the different types but not necessarily how to use them. Lighting companies can tell them what will work best for their project. It's not all cut-and-dried, but until they actually test it they might find out that something may work better for their project.

Zeiler points out a food company that had a system designed for tungsten lighting. It was using too much power, so they switched to metal halite lamps. "They didn't put out light in the colors they needed," he says. "Those things should have been determined before the system design."

In the food industry, for obvious reasons, light sourced with glass has to be shielded from the product. The lamps will overheat. The fluorescent lamp was invented in the 1930s. It was designed to meet specific applications. The main thing for longevity and brightness is that if it gets hotter or cooler the output will go down, Zeiler says. "If you have a plastic box with a lamp inside, air needs to get in there to hold the temperature down. The output will decline up to 50 percent. The lamp driver watches the temperature and holds the light level constant. If the temperature goes up, the lamp driver adds power to maintain brightness. It could go to thermal runaway [the driver adds more power to hold brightness, but the result is less and less light]. In this case, just put a fan inside the box with the lamp. It will raise the ability to get rid of the heat four times."

While the cameras can pick up any color, the light has to have the target color, Zeiler says. We all know almonds are brown, but you're looking for black or yellow (defects) so the light source needs those. "French fries have to be white. If they're too yellow, they're out so the light source has to have features that will reject yellow. You can use tungsten or metal halite. They have the color bands."

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