Electronics > Projects, Designs, and Technical Stuff
State of the art white LED efficacy?
mzzj:
--- Quote from: T3sl4co1l on January 17, 2020, 02:41:18 pm ---I'm not sure if there are any physical limits to the quantum efficiency, i.e., one photon emitted for every electron crossing the junction. I know the high index of refraction of the semiconductor is a big problem (total internal reflection for most randomly oriented photons), and they're using patterned surfaces to help that (and probably antireflective layers?).
Perfect lime green is 660 lm/W (or whatever the exact figure is), so white can't possibly be anywhere near that. A flatter (solar?) spectrum is supposed to be more like 230? So, anyone claiming anything that high, with phosphors, is full of something.
I wonder if they've developed bi-level or wavelength-doubling phosphors?
Tim
--- End quote ---
bad luck with led materials or what when eye response and led efficiency vs wavelenght are nearly inverse functions of each.
https://www.nap.edu/openbook/12821/xhtml/images/p2001a18fg70001.jpg
T3sl4co1l:
Indeed, it's a shame LEDs (direct wavelength) aren't more efficient in that gap. Which, heh, GaP is indeed your classic green LED material -- it's not very efficient, hence being restricted to indication only.
Indeed, they're so inefficient that modern high-efficiency greens are InGaN blue, either paired with a (much cleaner and more total coverage*) phosphor, or with the phosphor or quantum dots mixed into the junction itself (emitting green directly, but still costing 3V to forward bias).
*Compared to white LEDs, which intentionally use a broad spectrum phosphor (or mix), with partial coverage (some blue is transmitted).
My comment about bi-level or doubling phosphors is (or would be?), rather than discarding the energy difference between blue and yellow (the phosphor is the second hottest component after the chip!), it could generate, say, two red photons, if the energy levels work out correctly. A deeper (indigo or UV) source could give yellow or green at very high efficiency, and therefore very high efficacy as well. The remaining gaps (cyan, orange, red) could be filled in, at somewhat lower efficiency, with more conventional emitters and/or phosphors, if maximum CRI is desired.
Tim
mzzj:
--- Quote from: splin on January 17, 2020, 12:30:16 am ---
Good point, but witrh higher efficiency, temperatures will be lower. Samsung LM301B LEDs lose 6% flux at 85C, but forward voltage drops by 3% so efficiency loss should only be 3% from 25 to 85C provided the driver is suitably designed.
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You know what they say about "typical" specs in datasheets? >:D
Reading "typical" values off the graph and relying on them to 3% accuracy is bit optimistic to my taste. Could be 30% off as well. :-DD
Even the initial guaranteed values leave some leeway:
Samsung maintains measurement tolerance of: forward voltage = ±0.1 V, luminous flux = ±5 %
Samsung is also pretty quiet about lumen maintenance (lifetime) of the LM301B.
BTW: Current E27 (A19) replacement bulbs probably run even hotter than 85Cel:
I checked two 10W light bulbs with FLIR E4. Bulbs have been turned on for last 6 hours: One hanging from bare bulb socket measures 101 Cel ! and another brand in large, open, "inverted salad bowl" luminaire measured at 99 Cel :phew:
Bulbs were rated for 1000...1055 lumens.
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