Researchers tout advances in development of pure white LEDs

Researchers at the Indian Institute of Science are making some fairly bold claims about their latest advance in the realm of white LEDs, boasting that they are now getting closer to the "Holy Grail of the illumination industry." That, they say, is a white LED that produces a pure white light suitable for everyday use (as opposed to the "warm white" LEDs used in pricey bulbs like the one seen here). The big advance here, it seems, is the development of the first LED based on a "new phosphor from semiconductor nanocrystals of cadmium sulfide mixed with manganese." While we're admittedly not entirely sure what all that is, the researchers claim that the result is an LED that produces a stable and constant shade of white light, which is "superior in overall performance" to previous white LEDs. They're apparently not fully satisfied with the results just yet though, and are reportedly working to boost the efficiency of the LEDs to make them more suitable for everyday applications.

[HaX80r @ Sep 26th 2007 3:57PM]

Interesting.

[Raimon @ Sep 27th 2007 7:47AM]

In spain you can find very good leds at a lower prices in this web www.e-ponts.net/leds

I saw a 9W for only 30 € it replaces the halogen 50W.

I saw them in some places and look well. 400 lumens

[Rusty @ Sep 26th 2007 4:10PM]

riddle me this....we all know that the LED's use DC voltage to operate, and household current is AC. You will have to have some sort of step down transformer to drop the AC from 120 (USA) volts to 12-24 volts AC, then rectify the voltage to DC. Isn't the step down transformer going to "waste" electricity? I hear stories about environmentalist telling people to unplug the "bricks" when you aren't actively using them.
Yes, a bulb will have the step down inside the bulb enclosure, and would be disconnected when the light socket is off, but when on, isn't the transformer wasting "juice" in the step down process?

[staniel @ Sep 26th 2007 4:17PM]

First, rectifying an AC signal to full DC is not hard at all, just 4 diodes and you're done. Especially when talking about diodes, as they are not sensitive to non-uniform signals (you don't need a filter).

Second, depending on the LED voltage drop, you technically do not need a transformer at all. Granted, it can get stupid sometimes, but if you had an LED with a 3V drop, then if you wired 40 in parallel 40*3=120V. Bingo, no transformer needed.

Also, technically, you don't need a rectifier either, depending on the LED response time. You might be able to see the 60hz flicker out of the corner of your eye, but probably not.

[joel @ Sep 26th 2007 4:31PM]

Have you ever used LED christmas.... er I mean "Holiday" lights that use LEDs. No rectifier that I can spot, and definitely no capacitor to smooth things out. If you move those things at all the 60 Hz flicker becomes nauseatingly apparent.

[iDevin @ Sep 26th 2007 4:32PM]

Not as much energy as an incandescent bulb wastes to heat. The average incandescent bulb uses 60 watts. An equivalent compact fluorescent lamp uses about 14 watts. A Macbook with adapter uses 16.6 watts when idling with display on. A current technology LED bulb that is equivalent to a 70 watt incandescent uses 9 watts (although the light won't behave the same way as CFL or incandescent light, so depends on the application). The amount of power loss in the DC conversion is pretty minimal, compared to the potential energy savings of using LEDs instead of CFL, that is of course assuming they can make the technology better within the next few years.

Sources:
http://www.apple.com/environment/resources/specs.html
http://www.treehugger.com/files/2007/02/led_bulb_replac.php
http://en.wikipedia.org/wiki/Compact_fluorescent_lamp

[dv @ Sep 26th 2007 5:05PM]

unplugging unused wallwarts/surge protectors for environmental reasons is utter crap.

in ideal theory, a transformer does not consume energy and only converts energy. in the non-ideal and realistic world, transformers operate with >95% efficiency and emit only a tiny amount of heat compared to the amount of power they convert. if nothing is even consuming power, a realistic real-world transformer consumes only a small fraction of a watt.

just to show you the math, if a plugged but unused wallwart is emitting 0.5W of heat (a very realistic number), unplugging the wallwart for 24 hours saves the same amount of energy as an average single electric stove plate consumes in 30 seconds, or that a car consumes in less than a second.

hence, don't be penny-wise and pound-foolish; there are better ways to save energy than unplugging wallwarts.

[McFly @ Sep 26th 2007 8:22PM]

dv.. you do the math
only 0.5W you say? that's per brick, so assuming only half the population of NZ has cell phones and they all leave the brick in the socket cause hey, what's half a watt per day, and that's like 2,000,000 people. so we're only wasting 1,000,000 W per day... peanuts

[Frankenstein Black @ Sep 26th 2007 4:24PM]

Um, "suitable for everyday applications". Cool, light that will create healthier more robust inside home grown strains of Uber Cannibus, er Hemp, which of course will be used for stronger, clothing and stuff ;^)...
Oh, and I have NEVER touch the stuff...

[ikepod @ Sep 26th 2007 4:31PM]

Hey, Donald Melanson! The researchers aren't the ones making that claim, they just sent in a nice technical letter announcing some interesting preliminary results to the Journal Of Phsyical Chemistry C: http://pubs.acs.org/cgi-bin/sample.cgi/jpccck/2007/111/i37/pdf/jp074703f.pdf

The people making the claim that it's 'closer to the "Holy Grail of the illumination industry."' are the people over at PhysOrg. The actual primary source, the technical letter is a lot more modest.

[CB @ Sep 26th 2007 4:32PM]

Changing voltages doesn't waste hardly any energy. You just use less 120V current to get a given 12-24v current. For example, 1 amp at 20V = .125 amp @ 120V. These use the same wattage.

@ Staniel, you mean 40 in series (not parallel to get a 120V drop.

LED's are the energy efficient solution we need. Fluorescents are not good, too much mercury.

[JeffDM @ Sep 27th 2007 1:47AM]

CFLs can be recycled to reclaim what little mercury they still use.

It's a very tiny amount, particularly compared to the amount of mercury that's emitted by a coal power plant that might be use to light the bulb over its entire life.

LED would be nice, I'd like to see it get affordable, and I hope there's enough surge protection built into them, because I'd hate to buy $100 LED bulbs and have them zapped by lightning.

[Ordeith @ Sep 26th 2007 4:37PM]

Looks like something used by Dr. Who

[Mile @ Sep 26th 2007 4:44PM]

Finally, something worthwhile out of Indiana.

Oh, it's the Indian Institute of Science?

Nevermind.

[pauly @ Sep 26th 2007 4:53PM]

They are going to have some stiff competition from CREE based in North Carolina.

http://www.cree.com/press/press_detail.asp?i=1189169857943

[firebat45 @ Sep 26th 2007 8:59PM]

Whether it's one person and .5 watts or 2 million people and a million watts, it doesn't matter. If those 2 million people each cut back on car usage by, oh, 1 second, they'd be saving 1 million watts when all added together. His logic still stands.

[McFly @ Sep 28th 2007 2:08AM]

should i walk you thru this again?
your insignificant 0.5W * the number of people who think it's ok to waste power as long as it's only a little = A_HUGE_EFFING_NUMBER W
if we can save 1 million watts by driving for a second less each day, why not unplug your unused phone charger and save 2 million?
it's not ok to waste power, full stop

[Brian @ Sep 26th 2007 10:58PM]

@staniel - Yes, you do need a rectifier. LED's are one-way streets, hence the "Diode" in Light Emitting Diode. And their response time is very fast - you'd see the 60Hz cycling.

@Maverickfiveo - Cadmium is on the RoHS list, but cadmium selenide is not. Nanocrystalline - or, more appropriately, nanoparticulate - CdSe is what we call a quantum dot; particles much less than 100nm in size start to exhibit interesting quantum effects. In the case of quantum dots, all light below a certain wavelength is absorbed and re-emitted at one particular wavelength, which is tuned by changing the size of the quantum dot.

[CB @ Sep 27th 2007 5:05AM]

I 've just bought those 20 LED downlighter bulbs, the 1 watt versions and everyone hates the light they put out.
I say they just need to get used to it and they must think of the children and the fact I've reduced the watt consumption in the kitchen from 550 to 11.
I 'm keeping it to myself that I hate the light as well.

[Jhar257 @ Sep 28th 2007 4:48PM]

Lot's of people are talking about wasting energy, well these materials have soemthing like a 2 % quantum yield, that means 2 % of the energy input into the quantum dots comes out as light and the rest is converted to heat i.e. a lot of wasted energy. These are just a start, and while in the right direction won't be of significance for some time. Nice research though.

[Maverickfiveo @ Sep 28th 2007 5:03PM]

Correct me if I'm wrong, but isn't cadmium sulfide a RoHS-banned substance? (just like mercury in the flourescent bulbs) I work with phosphor scintillator screens in our engineering and we've had to migrate away from any scintillators with cadmium in them for that reason. Does that means these LEDs will be RoHS non-compliant? That could be damning for them...

[malditoelectricista @ Jan 4th 2008 12:13PM]

If you put 40 leds in series, Theoretically, you don't need a transformer, but if one of them fails then the entire circuits fails and no more light is available, therefore, this configuration isn't practical. A transformer is needed, but the waste of energy of this device is low, now if you think that is low, but X 2 million... well light bulbs only convert 30% of the energy in light... sorry, but in the search for better technologies we must go step by step, and obviously this isn't the best way to achieve a 99.99% of eficiency. I think we go in the right way. (sorry for my english, I'm chilean)