Do super-red LEDs emit 'pleasing' light?

Hello Jim,

Yes, I thought about that. Like an obstruction light on top of a hill. We are going to get one of those some day on our hill. Progress on that project is rather sluggish but when you see one of those blinking lights at CP when turning final onto 31 you know where I live :-)

There won't be a fancy driver, just a 74HC164 driven by a uC. But that can still be PWM'ed to some extent. Might not work in this case since the lights will have to indicate pretty rapid changes.

Regards, Joerg

Hello Sjouke,

Philips has the nicest one AFAICT but it'll set you back about a Dollar a pop.

Regards, Joerg

Hello Richard,

Interesting. Here I am, a guy who grew up in Germany and didn't even look at one of their mainstream mfgs. They are only known for their 230V lamps though over there.

They have versions they call super red at 643nm. Unfortunatly only surface mount which I can't use here and pretty weak, 3-7mcd for the super red.

Regards, Joerg

Hello James,

That would not be good. Why do you think that is? Dirty process? Skimping on silicon real estate?

Regards, Joerg

But I'm not expecting a single wavelength, just wavelengths that obey the laws of physics. Okay, so "about 660 nm" means some spectral distrubution about 660 nm. There is still a question that the 660 nm (and shorter) part of that spectrum requires more voltage than is being supplied. Where does the extra energy come from?

Mark

And note that thermal effects aren't going to have much effect -- E at room temp is around 0.025eV, enough for only delta 0.07mV (compare that to the tempco of whatever it is, probably similar to Si's -20mV/K).

Tim

-- Deep Fryer: a very philosophical monk. Website:

Note that this is highly affected by directivity. Whether directivity is acceptable again depends on the application. Clear housings are usually directional and very bright. Colored housings are diffuse.

Osam calls the 661 nm "hyper-red". Look at page 106 in that pdf - wired versions. They say voltage is 1.8 (2.0) volt or something - mind the tempco I would say.

Osram also give the lumen output in their data sheet - that is the overall output (how good the LED is at lighting a room so to speak).

Thomas>

What if you get a higher forward drop LED and connect a diode in parallel (backwards), and the connect a capacitor in series with the combination, and connect one end of this lot to a logic gate and the other end to the inverted logic signal, and put a few kHz square wave into it, to make a capacitive voltage doubler. All of the logic could be in the uC, the gates below are just to illustrate the idea.

Chris LED --------||---- | | |\\ | -------| O------------------------------ |/

Hello Zak,

In this app highly directional output would not be good so I need to go with diffuse lenses. Clear versions look nice, but...

That reminds me of the first time I went to Spain. Little grocery stores were called "Supermercado". Wow. Then we saw a really big one like a Safeway here in the US. It was called "Hypermercado". I almost spilled my coffee.

Regards, Joerg

Hello Chris,

Nice idea, it's the push-pull trick they use in car audio. At least used to when I was young and people were content with 100W or so :-)

But, being a cheapskate I am also using the LEDs as part of the polarity reversal protection in case someone inserts the batteries the wrong way.

Regards, Joerg

I understand it's real hard to grow good GaN crystals, and that this is part of Nichia's advantage. OTOH, Cree sources many of the clone-makers dice, and Cree is top-notch, so I don't know what the deal is. Maybe someone's growing them in their bath tub!

That would be skimping on GaN of course. I don't know what the physical cause for the rapid aging is, but I've seen several reports. Watson A. Name posted here in sed, for example, that his eBay wonders' output faded to nothing remarkably quickly, though I can't find his posts for anything.... By contrast, the Nichia parts (NSPW500CS, IIRC) handle severe abuse (e.g. 60mA continuous) with aplomb.

Best, James Arthur

Some white LEDs are blue with a fluorescent material in the package to convert the blue light into an approximation of white. The fluorescent material degrades with time.

Regards, Allan

So, how do you get population inversion without enough energy for the emitting jump? Maybe you need to widen your choices of climbing the energy tree?

Why should there be population inversion in ordinary LED's? We're not talking about laser diodes. (Besides, in my experience with lasers, the voltage IS more than enough to produce the photons).

The external voltage source is the only source of energy here. So my simple picture of each electron getting at most e*V of energy is wrong somehow. I've Googled to get several LED band-energy diagrams, but they don't address my question. I suspect electrons are transferring energy to each other, so that some get enough to produce light.

Mark

p.s. sorry about straying off-topic on the s.e.d group :-)

On white or blue LEDs in an epoxy package, the UV causes the epoxy to turn dark and yellow with age. The plastic cased ones are more immune to this.