Re: LED breakthrough may revolutionize lighting
- From: don@xxxxxxxxxxxxxx (Don Klipstein)
- Date: Sun, 26 Oct 2008 06:35:44 +0000 (UTC)
In <f49121c8-1457-4df3-8e60-307a07de0fd9@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
rpautrey2 wrote the following that caught me a bit as hype:
LED breakthrough may revolutionize lighting
http://eartheasy.com/article_led_breakthrough.html
Purdue researchers achieve LED production breakthrough which clears
the way for low-cost, high-efficiency lighting.
LED light bulbs are about four times more efficient than conventional
incandescent lights
Same as CFLs - and that is for better than is achieved by most LED
lighting products.
and, because they contain no mercury, more
environmentally friendly than compact fluorescent bulbs.
Although this is true when you have LED outperforming CFL (which is not
common in lighting), keep in mind that CFL is better for the environment
than incandescent - and close to a draw if even considering only mercury!
Coal combustion is a huge source of mercury pollution, and CFLs achieving
6,000 hour life when replacing incandescents as low as 60 watts will
actually not increase mercury pollution even if their recycling rate is
zero!
And to improve upon that - www.lamprecycle.org! Also, Home Depot takes
worn-out CFLs for proper disposal!
LEDs are also longer lasting than conventional lighting, lasting perhaps
as long as 15 years before burning out.
"Perhaps as long as"?
What about the widely-touted 100,000 hours?
What about better major brand white ones achieving 50,000 hours before
fading by at least 30% "with good treatent" including heatsinking to
extent of achieving temperature significantly cooler than "dataseet
temperature limit"?
Also, rated efficiency tends to be achieved when either "heatsinkable
surface" or the hottest internal point of the chip(s) of the LED is cooled
to 25 degrees C!
"LED technology has the potential of replacing all incandescent and
compact fluorescent bulbs, which would have dramatic energy and
environmental ramifications," said Timothy D. Sands, the Basil S.
Turner Professor of Materials Engineering and Electrical and Computer
Engineering at Purdue University.
But LED lights now on the market are prohibitively expensive, in part
because they are created on a substrate, or first layer, of sapphire.
The Purdue researchers have solved this problem by developing a
technique to create LEDs on low-cost, metal-coated silicon wafers,
said Mark H. Oliver, a graduate student in materials engineering who
is working with Sands.
It has been brought to my attention a few times already over the past
many years how there were supposed to be in-the-works good-high-efficiency
LED chips with silicon substrate!
LEDs designed to emit white light are central to solid-state lighting,
semiconducting devices made of layers of materials that emit light
when electricity is applied. Conventional lighting generates light
with hot metal filaments or glowing gasses inside glass tubes.
The LEDs have historically been limited primarily to applications such
as indicator lamps in electronics and toys, but recent advances have
made them as bright as incandescent bulbs.
The light-emitting ingredient in LEDs is a material called gallium
nitride, which is used in the sapphire-based blue and green LEDs,
including those in traffic signals. The material also is used in
lasers in high-definition DVD players. The sapphire-based technology,
however, is currently too expensive for widespread domestic-lighting
use, costing at least 20 times more than conventional incandescent and
compact fluorescent light bulbs.
One reason for the high cost is that the sapphire-based LEDs require a
separate mirrorlike collector to reflect light that ordinarily would
be lost.
Cree Inc. has been for a goodly few years already been achieving such
LEDs with silicon carbide substrate - and even appears to me to have
achieved transparent silicon carbide!
A mirror under the chip is dirt-cheap!
<SNIP stuff I consider more-worth-deleting to edit for space>
Incandescent bulbs are about 10 percent efficient, meaning they
convert 10 percent of electricity into light and 90 percent into
heat.
That good? I have yet to find a 120V 100W A19 incandescent even rated
1750 lumens of 7-+ efficiency at converting input to electromagnetic
radiation of wavelengtths 400-700 nm!
"Its actually a better heater than a light emitter," Sands said.
By comparison, efficiencies ranging from 47 percent to 64 percent have
been seen in some white LEDs, but the LED lights now on the market
cost about $100.
Please tell me mfr, part number and supplier for any white LED that I
can buy that achieves 47-64% efficiency, along with conditions for
achieving such efficiency. That sounds to me like about 140-190
lumens/watt.
"When the cost of a white LED lamp comes down to about $5, LEDs will
be in widespread use for general illumination," Sands said. "LEDs are
still improving in efficiency, so they will surpass fluorescents.
So surpassing of fluorescents has yet to be achieved? I thought that
has been recently achieved already by small margin with lower wattages
with great upfront-cost-per-whatever.
Everything looks favorable for LEDs, except for that initial cost, a
problem that is likely to be solved soon."
He expects affordable LED lights to be on the market within two years.
Two remaining hurdles are to learn how to reduce defects in the
devices and prevent the gallium nitride layer from cracking as the
silicon wafer cools down after manufacturing.
"The silicon wafer expands and contracts less than the gallium
nitride," Sands said. "When you cool it down, the silicon does not
contract as fast as the gallium nitride, and the gallium nitride tends
to crack."
Sands said he expects both challenges to be met by industry.
"These are engineering issues, not major show stoppers," he said.
Read the posting that I quoted from if you need to see everything that I
snipped. And buyer beware!
- Don Klipstein (don@xxxxxxxxx)
.
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