Moores Law

When do you think that we will reach the heat and current limits on on LED technology?

It seems to that we are rapidly approaching the limits of what the LED's will take and our ability to move heat away from them.

Has there ever been any experimentation with Copper as a heatsink?
What about SILVER? It is not really that expensive if you consider that some lights out here seem to sell for $$$ Lots of cash.
Unless we start moving to new materials I think that we will hit those limits soon.
Yaesumofo

IMO, Moore's law applies. Between OLEDs, diamond substrates, and simple extrapolation of existing technology, progress will continue! Just look at what you could get bin-wise from Lumileds a year ago vs today. Yeah, we complain about bins, but the best keep getting better!

Larry

the main problem with leds, is the joints. even silver wouldn't really help that much if we can't provide a better thermal joint between the slug and the heatsink. and even between the die and the slug.

one time, i attempted to rip a 5w emitter off a heatsink, and the slug was adhered so solidly that the die and the rest of the package just flew right off the slug!
really ticks me off that the die itself was damaged, because imagine making a luxeon light with one thermal joint /ubbthreads/images/graemlins/grin.gif

what i'd like to see with luxeons, is a larger slug at the bottom. it appears as if a little more room could be taken up to incrase the footing, and increase the surface contact area.

As long as the lumens per watt keep increasing, life will be good! A year ago I recieved my first Luxeon light, a BB500 N ranked LED (18 to 23 lumens at 350mA) Today I haul around a BB500 R2H, it puts out 39 to 56 lumens at 350mA and with the "H" it runs at lower voltage hence less total wattage.
I dream of a W ranked Luxeon III for a 2D mag mod next summer...it can happen! A Y ranked 5W Luxeon would be awesome also... they are already at X so it is very possible in the next year.
Now...imagine a 500 lumen 10 watt LS in a few years...

Hi. I'm new here. I discovered these forums a few weeks ago and found some of the discussions regarding future LED developments to be rather interesting. As an electronics engineer I became interested in lighting in general and LEDs in particular recently as a new hobby, and have found the concept of solid state lighting to be fascinating.

I think this whole heat issue problem for future LED developments is already solved with the introduction of the Luxeon III. I believe with the Luxeon III Lumileds did some things to keep the phosphors from degrading at higher power levels, as well as enhancing the die to heat sink thermal resistance slightly(from 20°C/W to 17°/C). As a result, they can now claim a lifetime(30% lumen depreciation) of 50,000 hours at a power level of ~2.6 watts.

The ability to deal with ~2.5W of heat is good enough for the future, and let me explain why I don't think there is any more need to deal with higher heat dissipation levels. Right now LEDs are about 12% efficient, so of the 2.6W power inputted, the package has to deal with removing (1-0.12)*2.6W or ~2.3W of heat. In maybe two years LEDs will be about 35% efficient, meaning 65% of the power inputted will show up as heat rather than the 88% now. Remember that the Luxeon III can deal with 2.3W of heat without any changes in lumen maintainence. This means when LEDs are at a quantum efficiency of 35% the die can be driven at a power level of 2.3W/0.65 or 3.5W. 1.2W of this will leave the die as visible light, the rest will show up as heat. A 35% quantum efficiency is ~75 lm/W, so this hypothetical Luxeon IV using the exact same package will produce 3.5*75 or 262.5 lumens.

Fast forward to the day when quantum efficiency jumps to 80%, or ~170 lm/W. I don't think we'll easily or quickly get much higher than this. The same package can now be driven at a power level of 2.3/(1-0.8) or 11.5 W. No more heat will need to be removed than the 2.3W that the Luxeon III package is known to be capable of because of the higher quantum efficiency. 11.5W at 170 lm/W is 1955 lumens. I believe the stated goal of the solid state lighting initiative is 1000 lumens per package and 150 lm/W by 2012. I think I've demonstrated that we already have the package to do that. I would rather that all future developments should focus on improving quantum efficiency, and to a lesser extent lumen depreciation. I tend to think we'll eventually have LEDs with 30% lumen depreciation at 200,000 or 300,000 hours once the mechanisms for degradation are fully understood.

N.B. I based my lm/W conversions for quantum efficiency on the fact that today's LEDs of 25 lm/W (calculated from the Luxeon III datasheet) are about 12% efficient.

And to think, when I opened this thread, I thought this was some kind of CPF law referring to flashlights, like; Moores Better

A question that's been bugging for a while now, this seems a good a thread as any to ask it;
Will there ever be a chemical combination that will produce a "real" white LED, as opposed to the phosphor over a blue led we have now? Looking at the specs for the blue and white luxeons really shows how much light is 'wasted' by having to shine it through a layer of phosphor. It should also give you better odds when playing the luxeon lottory, tint-wise anyway.

There are two other schools of thought on white LEDs. One uses UV light to excite a phosphor. This is similar to what a fluorescent tube does. You don't have to worry about light lost passing through a phosphor layer as with the current blue+phosphor LEDs, so you can get more consistent color. The other type involves using red, blue, and yellow emitters combined to give white light. It is tricky to get the ratio just right, and you have different forward voltages for each color. Unless these problems are solved, I think this method is the least likely to ever be used.

If I had to bet, I would say we'll see UV + phosphor as the dominant technology once the short lifetime problems with UV LEDs are worked out. You would have better consistency than is possible today as you're not trying to mix blue with yellow from the phosphor to get white.

Another thought on all this is that "white" in the general lighting industry will eventually come to mean ~5500K, not the typical 2700K to 3000K of incandescents. I see something like the warm white Luxeon as a stop gap measure meant to blend in with incandescent lighting. Once everything is LED, I think most people will prefer the more natural 5500K lighting that we already enjoy with our white LEDs. Studies have shown that any type of artificial lighting not similar to natural lighting is bad for you. This includes cool white and warm white fluorescents as well as incandescents. In particular I personally can't stand the yellowish light from incandescents, and prefer either 5000K or 6500K fluorescent lighting with good color rendering(I hate those cheap greenish cool white tubes as well). The standard of choice in the future will likely be something identical in color to today's full spectrum 5000 to 5500 K fluorescent lights. Good color rendering, and light similar to sunlight. The only reason some people might not switch right away is that they are "used to" incandescent type lighting. Like smoking, sometimes habits are hard to break, even when they are bad for you.

You don't have to worry about light shining "through" phosphor period. UV isn't needed. The blue light isn't filtered by the phosphor. The blue light excites the phosphor. The phosphor emits white light when excited. It's a fluorescent light; the phosphor is just excited through a different means than prior fluorescent lighting.

Then why aren't white led's blue dies with white phosphur instead of yellow?....

[ QUOTE ]
Then why aren't white led's blue dies with white phosphur instead of yellow?....

[/ QUOTE ]


Because there isn`t a white phosphor and what you see as white light is made up of all the colours of the rainbow added together, a rainbow, and very effectively a CD, breaks the light into the different colours.

White is Additively mixed with light,Primary Colours, red, green and blue are Added together to make white light.

Try it yourself:

http://javaboutique.internet.com/java_rgb

References to Subtractive mixing are about printers , like an inkjet, the use Secondary Colours, cyan, magenta and yellow because to select a colour you are Subtracting colour from the white of the paper.

With additive mixing and phosphors that fluoresce at long wave UV and visible blue, a yellow phosphor and a blue LED will give you white, yellow is actually red and green light.

Think if you want serious cooling look to the laser diode arrays:

http://www.nuvonyx.com/catalog2/single-bar.htm

Or where diamond isn`t the shape of the heatsink, its the material...

http://www.he-diamond.com/english/heatsink.htm

http://www.chm.bris.ac.uk/pt/diamond/end.htm

Remember that Lumileds innovation is in the pyramodial shape letting more light out as well as heat management.

Shuji Nakamura developed blue LEDs against a lot of competition:

http://www.sciam.com/article.cfm?articleID=000A2624-E2ED-1C73-9B81809EC588EF21

Dont think LEDs are at the Moores law point yet, doubling in power and halfing in price every 18 months, but think thery are climbimg the curve.

Adam

[ QUOTE ]
kakster said:
Will there ever be a chemical combination that will produce a "real" white LED, as opposed to the phosphor over a blue led we have now?

[/ QUOTE ]
This has been experimented with. Back in the 1990s, scientists experimented with zinc selenide (ZnSe) LED chips to produce white light without the use of a phosphor.
As far as I'm aware of though, these LEDs had limited brightness and short lifetimes, so the experiments were stopped in favour of blue LEDs with a yellow-emitting phosphor like we see today.