

The LED's Dark Secret (2009) - spectruman
http://spectrum.ieee.org/semiconductors/optoelectronics/the-leds-dark-secret

======
kazinator
> _Solid-state lighting won 't supplant the lightbulb until it can overcome
> the mysterious malady known as "droop"_

Counterpoint:

"Incandescent lighting will never make a come back against solid state until
it can overcome the mysterious maladies known as 'the fizzle and the pop', and
its voracious power consumption."

(We shouldn't forget fluorescent, by the way. And that's not solid-state; it's
tubes. In residential lighting, the competition now is really only between CFL
and LED.)

~~~
toomuchtodo
Fluorescent is more than likely on its way out, considering how fast the cost
of LEDs are coming down, their efficiency continues to increase, and their
longevity is many times that of their fluorescent counterparts (not to mention
you don't need to handle LEDs as carefully as fluorescent bulbs/tubes).

~~~
kazinator
Speaking of that, laims of LED longevity are troubling.

You better save your original receipts carefully. What if you get something
that is supposed to last 25,000 hours but in reality it only lasts 15,000? I
can imagine getting a refund, even a partial one, will be difficult, even with
the original receipt.

Firstly how do you prove it was only used 15,000 hours? It depends on how many
hours it was lit per day. How do you prove that the bulb you have in your hand
is the one for which the receipt was issued? A newer receipt could be used to
return an old identical item.

Is the store even around where you bought it? It's 30 years later now (so at
least your receipt is credible, by the date printed on it), but you have
nowhere to go. You only used that bulb 10,000 hours in its deployment
location, by your calculations, and it turned into toast. You have to turn to
the manufacturer for a refund. (A good argument for sticking to name brand
LEDs like Phillips.)

Many LED bulbs claim outrageously long lifetimes, but as of now, this has not
actually been tested; no deployed LEDs are anywhere near that many hours old.
Basically, it's a matter of faith. People are gambling that if they pay more
for and LED, it really will last as long as it claims.

(Don't get me wrong; I use LEDs. I have eight LED flood-lights, one LED room
light, and two LED range hood lights! I just wonder about the longevity. I
write the installation date on every bulb and try to save the receipts.)

~~~
HeyLaughingBoy
How is that different from incandescents? I switched my garage to LED lighting
because I never get anything remotely close to the claimed lifetime of
incandescent bulbs in the ceiling lights, no matter what brand I try.

In any event it doesn't matter whether or not the _actual_ life testing has
been done. Product manufacturers do accelerated life testing to estimate the
lifetime of the product. It's similar to asking how they know that a new car
shouldn't need warranty service for 6 years when it's only just been released.

~~~
Crito
Incandescents tend to be cheap enough that nobody cares. Even if they are
longer in the long run, the per-burn-out cost is cheap enough that it will
rarely hurt somebodies wallet. Easier to stomach 10 $1.00 burnouts than 1 $10
burnout.

See also: the reason why poor people tend not to shop at Costco.

~~~
Crito
s/longer/more expensive/

------
kefs
Cursory search revealed this from April 2013..

[http://engineering.ucsb.edu/news/699](http://engineering.ucsb.edu/news/699)

~~~
TheCapn
The author's reasoning for this posting is likely due to the Nobel Prize
announcement:

[http://www.nobelprize.org/nobel_prizes/physics/laureates/201...](http://www.nobelprize.org/nobel_prizes/physics/laureates/2014/press.html)

------
anigbrowl
I don't know if a 5 year old article is helpful really. Certainly in the film
world, things have moved on since that was written; large LED light panels are
common on sets now and throw out a huge amount of light relative to their size
and power consumption, eg
[http://www.litepanels.com/1x1_ls_bicolor.php](http://www.litepanels.com/1x1_ls_bicolor.php)

~~~
hackuser
I had thought LEDs produced a poor color spectrum for film. I see the linked
site advertises a color temperature "from daylight to tungsten and anything in
between". How is that accomplished (or is my memory of LED's spectrum poor)?

~~~
clarry
The diode itself produces only a peak in the spectrum. Phosphors are used to
convert the light to a wide spectrum. There are different kinds of phosphors,
and there can be multiple coatings of different types. So you can also have
different qualities -- and the quality can be very good.

~~~
hackuser
> The diode itself produces only a peak in the spectrum. Phosphors are used to
> convert the light to a wide spectrum. There are different kinds of
> phosphors, and there can be multiple coatings of different types. So you can
> also have different qualities -- and the quality can be very good.

Thanks for the explanation. I've been learning a little about light sources;
based on my limited knowledge, I wouldn't expect that the full spectrum (or
spectral power distribution (SPD)) of daylight could be replicated by hacking
together LEDs and phosphors, though perhaps the untrained eye would not be
cognizant of the difference. Can they really pull off 'daylight'?

~~~
aidenn0
They've made fluorescent tubes with daylight spectrum for a long time (I
recall seeing them available, but expensive in the 90s). Those work with
phosphors, so I don't see why an blue LED pumped phosphor couldn't work as
well as one driven by a near-UV mercury vapour lamp.

------
tokenadult
This article is a very good background explanation of the rationale for this
year's Nobel physics prize and a good overview of LED technology and its
history. I learned a lot here about the economic and manufacturing trade-offs
involved in promoting use of LEDs for indoor lighting rather than incandescent
bulbs. A worthy read for a day when LEDs are very much in the news.

------
andrewflnr

      At the current levels needed for general lighting, droop 
      kicks in, and down you go, below 100 lm/W.
    

In other words, at their worst efficiency they still kick incandescents out of
the park, and are competitive with fluorescents without the toxic chemicals.
Wake me up when they solve the problem, but don't expect me to panic in the
meantime.

~~~
evanrelf
[http://www.sciencedaily.com/releases/2013/04/130423102328.ht...](http://www.sciencedaily.com/releases/2013/04/130423102328.htm)
yay

------
myrryr
The answer was to have lots of little LED elements.

None of which put out a lot of power, but in parallel gave the light that was
needed.

in 2009, they were trying to replace a lightbulb with a single led.

------
jhallenworld
What's wrong with multiple LEDs per chip, each operating at their most
efficient range?

~~~
r0bfelty
Nothing, as far as I am concerned. That is what all the LED light bulbs on the
market are currently doing. The price has come down substantially in the last
2 years. I am replacing all my bulbs as they build out with LEDs.

~~~
ctdonath
Yup, prices have become quite palatable: still high, but between longevity (1
LED ~= 10 incandescent) and eliminating replacement hassle (obviate 9 climb-
on-something replacements), and that the color issue is resolved to my
satisfaction, they're preferable.

Only issue now is consistency in group replacements. While I'm replacing
independent bulbs as they burn out, things like a vanity with 12 bulbs means
dropping some $150 at once to replace all the bulbs so they will all be
exactly the same model. Styling & performance is still changing rapidly enough
that occasional replacement of a burnout in a group will result in
inconsistent bulbs, looking sloppy.

~~~
mjevans
Your vanity is probably specked for something similar to 30 or 40 watt bulbs.
You could replace with half as many bulbs (leaving old dead bulbs in place or
using some other socket filler) that produce equivalent light to reduce the
costs.

------
gone35
[Spoilers]

 _Each theory has its champions. Theoreticians at Philipps-Universität Marburg
support Auger recombination [...]. Meanwhile, Hadis Morkoç’s group at Virginia
Commonwealth University seconds Schubert’s support of electron leakage [...]_.

Well, the consensus has progressed quite a bit since: In recent years there's
been increasingly convincing evidence that Auger recombination _is_ the
dominant effect behind droop after all (see for instance [1]).

[1] [http://spie.org/x108666.xml](http://spie.org/x108666.xml)

[/Spoilers]

------
monochromatic
> Today’s garden-variety incandescent bulbs aren’t much different from the
> ones Thomas Edison sold more than a century ago. They still waste 90 percent
> of their power, delivering roughly 16 lumens per watt. Fluorescent tubes do
> a lot better, at more than 100 lm/W, but even they pale next to the best
> LEDs. The current state-of-the-art white LED pumps out around 250 lm/W, and
> there’s no reason why that figure won’t reach 300 lm/W.

If 16 lm/W is 10% efficiency, why isn't 300 lm/W an impossible 187.5%
efficiency?

~~~
jacobolus
One guess: incandescents pump out lots of infrared radiation, compared to
LEDs, and also a lot more red light.

Lumens, as a unit, are normalized to the sensitivity of human cone cells, so
the same amount of radiant flux in the green part of the spectrum is “more
luminous” than in the red or violet parts of the spectrum, and infrared
doesn’t count at all.

As a result, I’m not sure there’s any obvious way to measure an efficiency
percentage in terms of lumens/watt.

------
matmann2001
Quantum tunneling

