Why 5 Watt Stars \'die\'
So I had a very interesting chat with Christian. It is indeed a phosphor issue, the heat degrades it until it goes out of spec. It's basically a 10,000 hour (not 100K) LED underneath.
It seems the basis of the CRADA he has going with Lumileds is two fold, increase the overall efficiency (more light for the same energy in) and more important improve the color match. This is the biggie to them. Their market is in lighting, not LEDs for us to fiddle with. They want better control of the color so they can sell large arrays that don't have off color LEDs that 'stick out like a sore thumb'.
It's well understood that 'the right' way is RGB LEDs, but that's not what is being done.
He showed me the stuff for the upcoming DOE conference on the future of LEDs (he's a key player). The push is on for color matched 'white' LEDs for spot lighting (like table lamps) with the *bulk* of light in the future coming from OLEDs which have better efficiencies but poor current density. They're seen as a cheap way to go, you 'paper the walls and ceiling' with OLEDs for the bulk of the needed light, and use LEDs for the rest.
FWIW the 'hot ticket' for the next generation phosphors is 'nano technology', specifically a plastic film with tiny bits of various different phosphors 'grown' into it. The films are expected to be mounted *above* (not touching) the LED proper, thus getting around the heat issue. The films will probably end up being a micron or two (thousandths of a mm) thick. Years off, of course, but since we at LBL are building the 'Molecular Foundry', the upcoming DOE 'Mecca' for such stuff, we'll probably be near the sharp part of the cutting edge.
Doug Owen
So I had a very interesting chat with Christian. It is indeed a phosphor issue, the heat degrades it until it goes out of spec. It's basically a 10,000 hour (not 100K) LED underneath.
It seems the basis of the CRADA he has going with Lumileds is two fold, increase the overall efficiency (more light for the same energy in) and more important improve the color match. This is the biggie to them. Their market is in lighting, not LEDs for us to fiddle with. They want better control of the color so they can sell large arrays that don't have off color LEDs that 'stick out like a sore thumb'.
It's well understood that 'the right' way is RGB LEDs, but that's not what is being done.
He showed me the stuff for the upcoming DOE conference on the future of LEDs (he's a key player). The push is on for color matched 'white' LEDs for spot lighting (like table lamps) with the *bulk* of light in the future coming from OLEDs which have better efficiencies but poor current density. They're seen as a cheap way to go, you 'paper the walls and ceiling' with OLEDs for the bulk of the needed light, and use LEDs for the rest.
FWIW the 'hot ticket' for the next generation phosphors is 'nano technology', specifically a plastic film with tiny bits of various different phosphors 'grown' into it. The films are expected to be mounted *above* (not touching) the LED proper, thus getting around the heat issue. The films will probably end up being a micron or two (thousandths of a mm) thick. Years off, of course, but since we at LBL are building the 'Molecular Foundry', the upcoming DOE 'Mecca' for such stuff, we'll probably be near the sharp part of the cutting edge.
Doug Owen
