Accidental Invention - Warm White LEDs!
by Michael Graham Richard, Gatineau, Canada on 10.23.05
Light-emitting diodes (LEDs) are almost the perfect artificial light source: They last a long time (50,000 hours), are very shock resistant, don't produce much heat and are very energy efficient. The "almost" part is because they are still relatively expensive (that can be solved) and, until now, didn't produce a very appealing light-color. Originally, they only produced red, yellow and green light. Then came the blue LEDs which were made to produce more or less white light, but anyone with a LED-flashlight on his cellphone knows that it's still very blue-ish. But all of this could change thanks to an accidental invention by Michael Bowers, a graduate student at Vanderbilt University. He was trying to make quantum dots when he discovered a way to make LEDs produce white light. "I was surprised when a white glow covered the table," Bowers said. "The quantum dots were supposed to emit blue light, but instead they were giving off a beautiful white glow."
The Department of Energy estimates LED lighting could reduce U.S. energy consumption for lighting by 29 percent by 2025.
Thanks to thanks Ben Clemens for the tip.
Update: Jamais at Worldchanging has a good post about this.
::Accidental invention could light up the future, ::Accidental Invention Points to End of Light Bulbs, via ::Slashdot, ::Light-emitting diode at Wikipedia
Hardly the first warm white LED. Luxeon (makers of the brightest LED's I know of) has them:
http://www.lumileds.com/products/line.cfm?lineId=12
There are also other companies that make standard 5mm LED's in a "warm white" color (I happened to be researching this last night for building myself some fake candles to put into pumpkins next week). Probably not a natural (pure chemical) color, but a combination of chemical color and some colored optics on top of the LED itself (pretty standard practice).
I'm curious about this because I saw pure white LEDs last year in a prototype flat screen developed for helicopter avionics. The civilian sector keeps re-inventing the wheel...
Pure white is one thing, they're going for a warmer (read: Yellower) light of the sort we have in incandescent bulbs. Pure white tends to get a bit harsh, that's why (beyond the technical reasons) most indoor lighting does have a yellow cast to it - it's just more soothing and more liveable.
Yes, warm whites, like other white LEDs, have a phosphor over a blue LED. Yoldal (www.yoldal.com) make a nice one they call 'sunny white', I sell those at www.ledsales.com.au
Couple factoids:
Leds are less efficient than flourescents. Calculating light output vs. electricity consumed. Repeat: It is a myth they use less elec per overall light output.
Leds get their savings by measuring light at just the area at which it is pointed. There is no ambient light measurement in LEDS.
The flourescents come out ahead when measuring omnidirectional nature of the light.
Leds are cheaper when we consider their longevity etc.
Check it out. Do the math. Watch the test setup to ensure OVERALL light is measured.
From what I have read, the current energy efficiency of LEDs is lower than fluorescents, but the max theorical efficiency is higher than fluorescents. Don't know how hard it would be to get there, though.
As for their directional nature, it is true when talking about single LEDs, but the bulbs that are and will be sold contain many leds and are designed to give omni-directional light.
My understanding is that this is significant because it has the potential to make LED manufacturing a chemical, rather than a micromechanical process. In theory you could stir up a big batch of LED goop, and coat things with it during the manufacturing process.
Conventional white LEDs are really tricky to make, requiring lots of 'doping' with strange chemicals to get the right light balance.
Sounds like a great breakthrough, but just to note, what was discovered is NOT a new type of LED. LEDs are just doped semiconductors (p-n junctions) that emit light. What was discovered are quantum dots, much smaller (hence the quantum confinement) and manufactured in a totally different way. The result? It's a great first step, but since there's no large scale manufacturing pipeline for QDs right now, low cost production for consumers is 5-10 years off.
-Brian (chemistry grad student)
Thanks Brian. I was a bit unsure about how to label the invention since most of the news coverage of it calls it LED (but I know that it is almost always inaccurate when it comes to scientific matters), but then they also talk about quantum dots. I figure that the quantum dots would help the production of a new type of LEDs...
Anyway, thanks!
The _first_ development of "warm white" or "sunny white" LEDS was for, of all things, the model railroading hobby. A manufacturer of lighting modules for the hobby was unhappy with the choice of either yellow or blue-white for lights, and approached several LED manufacturers to have them custom-tint some. I've found web references as early as Feb 23, 2003 to their availability, and I know he was experimenting with them for several months before they came up with a formulation he liked. (google groups: warm white LED "richmond controls")
Indeed, the important part of this is the quantum dots. Mr. Bowers managed to manufacture his quantum dots, also known as nanocrystals, to produce white light. Quantum dots were only known to produce white light by mixing different sizes; Bowers says his dots are all the same size. He only used an LED to "excite" the quantum dots. In the future, devices will probably be made to get electricity directly to the nanocrystals.
The Vanderbuilt posting lists Cadmium Selenide Nanocrystals as the magic formula.
Not exactly the mixture we want distributed across the world by the billions.
Latest update, if this news article holds true_
http://www.theinquirer.net/?article=27731
Then fluorescents are officially 2nd on the pole as of next year,
LED efficiency of 130 lumens per watt (current highly efficient white LEDs go up to about 80l/w, at a ridiculous price per lumen ratio).
Fluorescents are around 100-120 l/w, so if this holds true, it's the breakthrough everyone has been waiting for I think_
A side note, this is unrelated to the quantum dot discovery it appears, so if combined with THAT discovery, it might increase efficiency (and more importantly, light quality) even more. LEDs in the next 1-2 years it seems are prepared now for a major leap in utility.