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EETE MAY 2014

A whiter shade of pale By Paul Buckley Scientists from Pen State in partnership with Soraa Inc., believe that some LED bulbs whites are not ‘whiter than white’ and that with the switch away from incandescent and fluorescent lighting, different degrees of whites may all look the same. Kevin W. Houser, professor of architectural engineering, Penn State, led the research team which asked 39 participants to observe various combinations of light sources and white objects to see how the light source affected perceptions of white. The results are reported in a recent issue of Leukos, the journal of the Illuminating Engineering Society. For years, companies have been adding whiteners to laundry detergent, paints, plastics, paper and fabrics to make whites look ‘whiter than white’. “Retailers have long been concerned with the color-rendering qualities of their lighting, but less aware how light sources render white,” said Houser. Not long ago, the only practical choices for home, office or commercial lighting were incandescent or fluorescent bulbs. More recently, compact fluorescent bulbs, which use less energy than incandescent bulbs, became popular, but compact fluorescents are not always accepted by consumers because of poor color rendition, lack of dimability, slow warm-up to full output and because they contain mercury. The most recent popular entry into home or commercial lighting are lightemitting diode (LED) bulbs, which are often even more energy-saving than compact fluorescents. While some LED bulbs will make colors pop, the vast majority do not showcase or differentiate the appearance of white products, according to Houser, because all white light is not the same. Different light sources contain different combinations of the wavelengths of light. A broad variety of wavelengths will create light that appears white to the human eye, but different mixtures of wavelengths will affect how colors are rendered. When it comes to seeing the color white, the light source is very important because of how product manufacturers make white products appear white using whiteners. Whiteners contain fluorescent materials that glow under violet and ultraviolet light. Sunlight, fluorescent light and incandescent light all produce some light in the violet and ultraviolet range. The whiteners used in consumer products work under those conditions, resulting in a bright white perception. However, most current LED bulbs use blue LEDs to excite a phosphor that then glows white, but produces no violet or ultraviolet light. The participants completed three tests - selection, forced choice and sorting - using five different light sources - a blue-pumped LED, filtered halogen lamp and three violet-pumped LEDs with differing levels of violet emissions. In the sorting experiment, the researchers placed six calibrated whiteness cards of varying whiteness on a table in a booth enclosed on three sides. They asked participants to arrange the cards in order of whiteness under each of the five light sources. Under the halogen light and violetpumped LED lights with 7 and 11 percent violet emission, the order was correct. Two of the cards were flipped under violetpumped LEDs with only three percent violet emissions. “With the LED with only blue pumping the phosphors, the order became random,” said Houser. “People simply couldn’t tell the difference between the cards under the blue-pumped LED, which is notable because blue-pumped LEDs are by far the most common type for general lighting.” In the forced choice test, two nominally identical cards were placed in each of two booths containing different light sources. Participants were asked to choose the card that was whiter under all of the permutations of each of the five light sources. “The light sources with higher violet component permitted the best discrimination between the targets,” said Houser. In the selection test, researchers asked the participants to look at a reference card in one booth and rank the cards in a second booth as either as white or whiter than the reference card. Again the blue-pumped LEDs did not fare well. The researchers noted that “engineering of an LED source’s spectrum is necessary for an accurate rendering of whiteness.” Publisher André Rousselot +32 27400053 andre.rousselot@eetimes.be Editor-in-Chief Julien Happich +33 169819476 julien.happich@eetimes.be EDITORS Nick Flaherty +44 7710236368 nick.flaherty@eetimes.be Christoph Hammerschmidt +49 8944450209 chammerschmidt@gmx.net Peter Clarke +44 776 786 55 93 peter.clarke@eetimes.be Paul Buckley +44 1962866460 paul@activewords.co.uk Jean-Pierre Joosting +44 7800548133 jean-pierre.joosting@eetimes.be Circulation & Finance Luc Desimpel luc.desimpel@eetimes.be Advertising Production & Reprints Lydia Gijsegom lydia.gijsegom@eetimes.be Art Manager Jean-Paul Speliers Acounting Ricardo Pinto Ferreira Regional Advertising Representatives Contact information at: http://www.electronics-eetimes.com/en/ about/sales-contacts.html European Business Press SA 7 Avenue Reine Astrid 1310 La Hulpe Tel: +32 (0)2 740 00 50 european Fax: +32 (0)2 740 00 59 business press www.electronics-eetimes.com VAT Registration: BE 461.357.437 RPM: Brussels Company Number: 0461357437 © 2014 E.B.P. SA ELECTRONIC ENGINEERING TIMES EUROPE is published 11 times in 2014 by European Business Press SA, 7 Avenue Reine Astrid, 1310 La Hulpe, Belgium Tel: +32-2-740 00 50 Fax: +32-2-740 00 59 email: info@eetimes.be. VAT Registration: BE 461.357.437. RPM: Nivelles. Volume 16, Issue 5 EE Times P 304128 It is is free to qualified engineers and managers involved in engineering decisions – see: http://www.electronics-eetimes.com/subscribe Copyright 2014 by European Business Press SA. All rights reserved. P 304128 50 Electronic Engineering Times Europe May 2014 www.electronics-eetimes.com


EETE MAY 2014
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