Solving the Mystery of the Green LED For Pure, Efficient White Light

120 billion in savings divided by 20 years. 6 billion a year saved, isn't that about 12 minutes of federal spending?

We've had green led laser pointers for years, isn't that basically the same thing as these?

@Mycellium

The lasing element in green lasers actually generates light in the IR spectrum (over 1000nm wavelength). That laser light is then passed through a special crystal (potassium titanyl phosphate, or KTP) which doubles its frequency. So that IR laser gets converted to a 532nm (green) laser.

IN BRIGHTEST DAY IN BLACKEST NIGHT...

I could swear that I've seen white LEDs before. Is it more efficient to have three colored LEDs (R,G,B) than it is to have one white one?

I don't know. I'm sure my reasoning is off.

Interesting...

Mycellium, I don't understand how you relate time and federal spending, but saving money is saving money no matter how you try to spin it. Efficiency is the key here.

"I could swear that I've seen white LEDs before."

White LEDs come in two varieties. Most of them are blue LEDs encased in a phosphor that converts the light into various other frequencies just a like a fluorescent light.

Others are composed of multiple LEDs, each producing one colour component. The more components you have the better light quality you can produce.

What they've done here is produce another shade of green.

@suggestivesimon Thanks for the explanation.

@Gajamaru I was partially joking, but only partially. That six billion dollars is spent in about 12 minutes by the federal government.

6 billion a year more for NASA? Sounds good to me.

I've always been under the impression that it is the YELLOW LED that poses the true challenge, since it easily washes out to white. Isn't that precisely why we use the smaller set of possible colors from RGB, rather than the infinite colors possible using the primary colors?

I'm pretty sure the first LED I ever saw was green. Or maybe it was red, but green was at least second. I'm left confused as to what this fuss is all about.

The 2011 spending budget is 3.55 trillion. So 12 minutes would be a little over $8 million

"I've always been under the impression that it is the YELLOW LED that poses the true challenge, since it easily washes out to white. Isn't that precisely why we use the smaller set of possible colors from RGB, rather than the infinite colors possible using the primary colors?"

No.

Your eyes can only detect 3 primary colours. There are 3 types of 'cones' with overlapping response curves; if you find a red a green and a blue that activates only one of the cones without activating the others you can reach all colours by taking some linear combination of those primary colours.

This only works in additive displays. If you make a light source with only one red, green and blue component you're going to get an inferior colour rendering index.

The way this works is that if you have a pigment which reflects only some frequencies of green light but not others the particular green you chose for your 'RGB-light' ends up mattering a huge amount. If you happened to choose a frequency of green that is closer to aquamarine the pigment may appear darkish green because it reflects it poorly; if you happened to choose a lime-green frequency of green the object might appear to be bright green because it happens to reflect that frequency of green rather well.

Having more colour components or broader emission peaks mitigates this effect. When a light source is close to a black-body of the desired temperature it is considered ideal, with a high colour rendering index.

Isn't it amusing how non clever non scientists can write amusing anecdotal comments and give stimulating insight to the truly educated (:

sorry that first non in my previous comment was an error.

"I'm pretty sure the first LED I ever saw was green. Or maybe it was red, but green was at least second. I'm left confused as to what this fuss is all about."

The 1st led's were red. The one you are thinking of was that yellowish green that was widely used in the 70's and 80's, but not an actual green. For LED's, and any display, or adjustable color light, you need the purest of all 3 possible colors, that way when they are mixed, they can produce other colors accurately. Green is used the most in any tv, lcd, plasma, etc. to produce white light - if you can look close enough at a pixel you would see 2 green elements, 1 red element, and 1 blue element arranged in a square.

True green has been the holy grail to making energy efficient LED displays, computer monitors and tv's. Right now you're probably looking at an lcd monitor which uses pigmented liquid crystals that are backlit by a white light source, but if you could remove the light source and have the pixels emit their own light, all color elements/pixels not used could be turned off, rather than just trying to block the light behind them (which is why you can see it is kind of grey instead of pure black until the monitor gets turned completely off) not to mention your monitor gets even slimmer!

Aww LED's!! Look at those LED's!! Ha Ha! I hope they LED the entire planet! LED's are so freakin' awesome! Minus the money saved, more important is the amount of generators in the United States of America and worldwide that can be shut off simply by replacing every lighting fixture with LED's! That makes me happy most. Especially when we perfect LED's for use in car headlights like Audi is doing and our engines don't have to work as hard for us to drive at night. :D Long live LED's!!

Keep up the good work NREL!