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Problem Solver Page 3

Electronics — November 2004
By Ben Ellison

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Is there a common standard for measuring screen brightness? A.C., via e-mail
Yes, sort of, but no, not really! Apparently it’s impossible to put a solid number on “brightness.” In the words of vision expert Charles P. Halsted, “Brightness is a subjective attribute of light to which humans assign a label between very dim and very bright. Brightness is perceived, not measured. The response is nonlinear and complex.” That may sound dry, but it’s actually a key point in a rant Halsted wrote to his fellow engineers, and their marketing colleagues, imploring them not to confuse brightness with luminance.

Luminance, whose definition is just too complicated to attempt here, is related to perceived brightness, and it can usually be measured. Units of luminance are expressed as candela per square meter (cd/m2) or, strangely, nits (from the Latin nitere, “to shine”). That’s the sort of “light intensity” measurement that you may be seeing in the display brochures (and in this month’s new products), which probably prompted your question. My experience is that screens with nit ratings of more than 1,000, look pretty bright, but screens with lower ratings do not necessarily seem less bright, definitely not proportionally so. I’m told that high nit ratings are achieved with intense backlighting but that factors like antiglare coatings, rich colors, and high contrast are also important to viewability, which echoes Halsted’s lengthy full analysis. Plus there are screen-brightening techniques like transflectivity that cannot even be conventionally rated for luminance.

Above all, keep in mind that for you, as a human with “nonlinear and complex” perceptions (isn’t it heartening that we can’t be quantified?), display performance is not fully measurable. Try to preview a screen in all the light conditions in which you’ll use it before you commit.

Got a marine electronics question? Write to Electronics Q&A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail PMYElectronics@ primedia.com. For fastest response, visit the Electronics Forum at www.powerandmotoryacht.com. No phone calls, please.

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This article originally appeared in the October 2004 issue of Power & Motoryacht magazine.

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