Low-energy LED invention wins Nobel prize for Physics


#1

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#2

(Nitpick. It’s for blue LED. High-efficiency comes after getting the thing emit at all. Though this may be somewhat true anyway, as there were early blue LEDs on silicon carbide but they sucked and brightness was lousy. Only with gallium nitride things went the right way. And with aluminium nitride things can go even to ultraviolet; too bad the prices of chips skyrocket as we get beyond 390…350 nm…)

The guy is showing a blue laser, on the photo, too! Not a semiconductor one, a gas one (He-Cd), but still, blue laser!


“Nakamura invented the blue-light emitting diode while working at Nichia, an unlisted firm, but received next to nothing from the company for the work until 2004, when a Tokyo court ordered Nichia to pay him a record 20 billion yen ($185 million). The company appealed and Nakamura settled for about $8 million.”

Such people deserve this kind of money. Not some derivatives-gamblers, not some ball-kickers.


LED light is pretty good, in comparison with CCFL. Instant-on, easy to dim, easy to adjust color (if RGB is used alone or together with white).

The white light however sucks. There is not much to do with the blue LED die, that’s pretty much the same for all the vendors. The white is made from blue by converting part to yellow via a phosphor, usually cerium-doped YAG (which can be also used as xray/gamma scintillator, so don’t throw away broken LEDs without scraping this yellow ceramic powder out; todo, try if it would work with a PIN photodiode as a low-power solid-state radiation detector). The missing parts of light at blue-green and red areas are responsible for the odd color rendition. The ratio of blue/yellow is what determines the color temperature. (Which then drifts somewhat as the junction and materials age.)

There are many possible formulations of the phosphors. I expect most of innovation in the LED light field to happen here, in next years, and in multichip assemblies with more colors (RGB, plus potentially others in between for better colors). (Plus the electronics, but that falls rather under smart-home and internet-of-things areas than under lighting, strictly said.)

My personal favorite (and I may be wrong here, and I did not hear much of buzz about it anytime recently) is a group of phosphor blends based on quantum dots. The size of the “dots” allows tuning the emission wavelength pretty well, and blending then can provide the spectrum as desired, without major peaks. (Europium-based phosphors used for red in CFL blends have a dense cluster of peaks in red area. You want smooth spectrum, ideally.) The question is, how they will behave, degrade under less than perfect encapsulation (humidity is a bitch, it degrades OLEDs pretty fast and many other materials don’t cope well too), and age.


#3

I remember years ago an article in Discover or Scientific American about people (I assume them) finally perfecting the blue LED and eventually it would be used in TVs, computer screens, and lights. And, well, here we are.


#4

Your information may be out of date, there are some wonderful white LED products on the market today. Yes, quantum dot phosphors would be even better, but not really necessary except for displays. In general, a bulb with frosted glass (like many of the more attractive CFLs use) is more than sufficient.


#5

That’s fairly possible, the developments happen fast. My LEDs may also be out of date. Or my desires just may be too high. Or a combination of all of that. It’s quite possible your “wonderful” is my “somewhat acceptable” and we’re talking about the same thing.

What phosphor blends are used these days, beyond Ce:YAG? (Actually used, not just described in trade literature?) Do the vendors specify them, specify the emission curves of the bulbs? The frosted bulb won’t do anything than diffuse the light, perhaps slightly filter it if it is tinted but won’t add the wavelengths that aren’t there (resp. are poorly represented).


#6

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