led at low current

And you can dress as Uncle Fester for Halloween. ;-)

I have a nephew who can do three loops. =:-O

Cheers! Rich

And on Halloween, you can go as Uncle Fester. ;-)

I have a nephew who can do three loops.

Cheers! Rich

That's bizarre. All they are defining is the property of green light. They don't mention anything about the actual output of the LED, so the spec is academic.

John

I read some time back on compoundsemiconductor.com, or some such, the quantum efficiency of certain InGaN LEDs was 100%, as in 1 photon generated per electron.

Lots of those get trapped in the high-index die material though, and just bounce around uselessly. Extraction efficiency, as in "number of photons that escape the die," was therefore less, like 33% or so.

Those numbers jive roughly with your measurements. Does that all sound about right?

Cheers, James Arthur

Ahh, the perfect answer to all the "I just patented the World's Neatest Invention, how to I sell it to a manufacturing company for big bucks?"

(answer -- Bwa ha ha ha ha)

The spec is slightly relevant: it defines the perceived impact of the spread of wavelengths of light that comes out of /this/ LED, under the test conditions.

So, it's a handy reference, but not all that handy.

Cheers, James Arthur

Hey, why not just patent the method and process of selling patents to manufacturing companies?

Oh, darn, that's been done.

Cheers, James Arthur

Brown

days.

y.

One problem: 1 Farad SuperCaps have about 10 uA leakage current at room temperature. This would discharge the cap from 4V to 2.5V in 1.7 days, not counting the LED current.

On a sunny day (Fri, 7 Nov 2008 07:48:17 -0800 (PST)) it happened Bob wrote in :

OK, did not know that. So, the sun will have to come up a bit more often, like once a day :-) I tried, long time ago, some small solar cell, I think even in normal daylight here it could deliver > 11.5uA. Once bought a calculator with a solar cell too, it also worked with artificial light. So maybe the idea will work anyways?

There are some lithium battery chemistries that are rechargable, like lithium-iodine. They last about 10 years in pacemakers.

My Tadaran primary lithium AA cell will supply 10 uA for over 25 years, with no charging required.

John

I know the specs say supercaps have that sort of leakage, but my experience is that at least many dont, epspecially when the voltage is down around 2-2.5 volts. We use them for battery backed RAM, and designed for 2-3 day minimum sustain. In fact I have checked RAM hold up out to 3-4 months in many cases. A combination of low RAM and battery leakage current.

I was talking about photons exiting the LED per electron through - as in combined creation and extraction. And blue ones (and white ones using blue dice with phosphor) do get better than green ones. A few on the market appear to me to be achieving 30-35% quantum efficiency at a current they are characterized at, maybe 40% at some reduced current.

There have been announced laboratory prototypes with quantum efficiency (generation and extraction combined) exceeding 50%.

As for separate figures for creation and extraction - I hear different stories about creation, but that the creation rate can be impressively high and that the extraction rate is usually disappointing - due to photons being absorbed by something in or on the die outright, or too many photons being reflected around inside the die until they get absorbed because the die material has a higher refractive index than its surroundings. Approaches to reduce the latter have included textured dice and truncated inverted pyramid shaped dice.

- Don Klipstein ( snipped-for-privacy@misty.com)

It thought it had slight handiness incase someone wanted to predict, based on photometric achievement and wavelength of an LED, the performance of a photodetector of known response as a function of wavelength and radiometric intensity.

- Don Klipstein ( snipped-for-privacy@misty.com)

Yep, that matches the stuff I've read and figured.

Thanks Don!

--James

Hey, look at this:

This started as an experiment, just to try a circuit, but I did it so that it would fit into one of our boxes. It works well enough that we may as well try to sell it. The Brat press released it for me a week or two ago.

If you come up with a nice small box of some kind, and especially if you do a cool picture of it, you can get a ton of press releases posted by sites like these, for free. That gets you lots of links. It's amazing how fast this works.

Apparently a lot of web sites want content, some so that they can seed the page with google click things or other sponsored links.

This "internet" thing might be useful after all.

John

It is the 'once you're dark-adapted' thing. "Dark adapted" and "emergency" do not fit together. Whereas walking in the [near-]dark and emergency do fit together ... so to say. A branch, a cable, a step or a rock that wasn't anticipated and you have the emergency.

I have an emergency light in the office that runs continuously. These are a set of white and blue LEDs running at 5mA or so. They are sufficient to actually move safely. All the cables, steps and carpets are visible.

Rene

te:

It would be astonishing if it were true.

I think the record luminosity output per unit power is still held by the larger low pressure sodium lamps at a bit over 200 lumens/watt based on the serendipitous sodium D-lines and quantum mechanics. Some of the semiconductor devices are getting very close now especially in the green to yellow boundary where the eye is most sensitive.

es

e is

ITYM written up by marketting men...

However, you work it though they have gained another order of magnitude improvement in the best LEDs quantum efficiency over the past 5 years. Specsmanship not withstanding that is quite an acheivement!

PS it is fun to dunk boring old common or garden red LEDs in LN2 they burn much brighter (assuming the thermal shock doesn't kill them first).

Regards, Martin Brown

In a powercut then all it takes is waiting a 30s to 1 minute in the total darkness before you try to move. That isn't such an onerous burden. After that you can see by the light of one of these standby LED devices although I would actually switch it on to use as a torch after walking across to pick it up. The point here is that in a powercut you always have a torch that you can find in total darkness. I grant you it isn't much use in a room full of smoke.

I think too many people have a fear of the dark. Witness all the dazzling kilowatt quartz halogen insecurity lights everywhere.

But at that current you have limited battery life a few hundred hours at most from AA cells. The idea of this low current trick is to have no significant decrease in battery life but the benefit some light when it is nominally "off".

Regards, Martin Brown