[opendtv] LEDs shine as replacement for lightbulb
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 16 Nov 2007 16:14:24 -0500
My guess is, though, that this approach will lead to the same toxic
waste problem the existing fluorescent light bulb replacements create.
The phosphors are the problem, are they not?
I kinda liked the idea of being able to tune the color of the light
bulb, with different mixes of R, G, and B. But I see the point about
that approach not creating true white light.
Bert
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LEDs shine as replacement for lightbulb
R. Colin Johnson
(11/16/2007 12:28 PM EST)
URL: http://www.eetimes.com/showArticle.jhtml?articleID=203101640
PORTLAND, Ore. What are claimed to be the first white light-emitting
diodes (WLEDs) to achieve a high color-rendering index were recently
demonstrated by an international collaborative team of researchers. This
could answer the last remaining stumbling block to universal adoption of
white LEDs to replace incandescent bulbs and fluorescent tubes.
White LEDs use a fraction of the power of the venerable light bulb.
Unfortunately, traditional LEDs by themselves emit only a single
wavelength. Consequently, the only way to get white light from LEDs is
to house red, green and blue LEDs in the same package, add yellow
phosphors to the inside of the lens of blue LEDs, or turn to new
materials, such as zinc selenide, which can simultaneously emit blue
light from its active region and yellow light from its substrate. Any of
these LED construction methods emit light that appears to be whitish,
which makes them suitable for general-purpose lighting, but color
rendering index (CRI) tests verify that none of these approaches are
suitable for professions who must have lighting that is able to
reproduce all the colors in the visible spectrum.
Now, Professor Elisabeth Holder and her colleagues at the University of
Wuppertal (Germany) have collaborated with professor Hilmi Volkan Demir
of Bilkent University, in Ankara (Turkey), on a new approach to crafting
white LEDs that they claim yields a very high color-rendering index,
making them suitable for professional users from graphic artists to
horticulturists.
The key to the new technique is to embed various types of inorganic
luminescent nanoparticles into a highly fluorescent organic polymer
base, then pumping the mixture with a near-ultraviolet LED. The result,
according to the researchers, is hybrid organic/inorganic LEDs that
produce white light that contains almost every wavelength in the
spectrum, and, thus, can render most any color accurately.
Key to the collaborative effort was marrying the organic and inorganic
materials. By taking a layer-by-layer approach, the researchers were
able to embed fluorescent yellow, green and red nanoparticles (using
cadmium-selenium cores coated with a zinc silicon shells) into a
fluorescent blue polymer matrix (polyfluorene), and subsequently tune
the mixture to attain a color-rendering index in excess of 80 (compared
with 100 for sunlight, over 90 for incandescent, 70 for phosphor-based
LEDs, and 65 for fluorescent tubes). With further optimization, the
researchers hope to improve CRIs upward toward 100.
All material on this site Copyright 2007 CMP Media LLC. All rights
reserved.
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