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Seeing Eye to Eye: An overview of spectrophotometers

(April 2008) posted on Tue Apr 08, 2008

Spectrophotometers are valuable measurement tools that can help prevent costly color-matching mistakes and improve the quality of your printed images. Here

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By Ben P. Rosenfield

“Any color we can perceive can be quantitated,” explains Hal Good, director of marketing services for Hunter Associates Laboratory. “The eye can perceive nearly 10,000,000 shades of color—very sensitive, but not repeatable or reproducible—and that’s why these instruments are used.”

Three distinct optical geometries are most commonly employed in the design of spectrophotometers: integrating sphere, 45/0 (also known as bidirectional), and multiangle. In general, the sphere type is the most useful for screen-printing applications.

Spectrophotometers designed with sphere geometry illuminate samples diffusely—from all angles equally—and pick up measurements about 8° from perpendicular with the color sample’s surface. Measuring at this angle, according to Bob Marcus, Datacolor’s business-development manager for formulation systems, “allows you to either include a glossy reflection from the sample surface or use a light trap to exclude the gloss from the surface.”

The primary reason to consider other optical geometries is if you frequently use fluorescent, pearlescent, metallic, or other specialty inks. If you work with these materials often, you should mention that early in your talks with spectrophotometer manufacturers so they can guide you to the most suitable type.

Spectrophotometers, as pictured throughout this article, come in two main flavors: handheld/portable  and benchtop models. If you intend to use the device solely as a tool to aid with color mixing in the ink room, a benchtop model might best suit that purpose because it’s a stationary unit that you can keep next to a computer. But if you want to use the spectrophotometer in different parts of the shop, the portable version is the safest bet. Benchtop units are generally more effective for time-intensive, routine-based tasks, such as building color databases, while portable devices are geared toward taking more convenient, on- the-spot readings.


Why you need a spectrophotometer

“Anything that you can measure, you have a better chance of control-ling,” says Larry Gold-berg, technical director at Beta Industries. “Things that you don’t measure will eventually become the cause of mysterious problems.”Owning a spectrophotometer can allow you to play a bigger role in process control, from prepress through production. (For more information about the spectrophotometer’s influence on color quality, see “Accumulative Density: A Powerful Color-Control Tool” on page 30 of this issue.)


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