Fading white LED's

[throbscottle]

I've noticed white LED's seem to fade away after a while. Some of the ones on our fancy toaster have nearly faded away altogether, annoying, but no big deal easy to replace. However, I have an illuminated magnifier (which Mrs is currently using as a lamp for knitting) which has a ring of white LED's around the lens. These now also appear to be fading, don't fancy having to replace them - will see how it goes.

So, how widespread is this problem? And recommendations for makes/technologies of replacement LED's please, which don't do this!

Cheers all

 

[ronsimpson]

Many white LEDs use phosphor to produce light. (they look yellow when not lit) The phosphor will ware out. Just like a CRT will ware out.
Driving the LEDs hard/ letting them get hot/ will shorten their life.
Some people think running a 10mA LED at 10mA is fine.
Cut off the leads so there is less heatsink.
Use small PCB traces so there is less heatsinking.
Put the parts in a hot box. (toaster)
Over drive the current.
Get low cost parts from a unknown Chinese maker. e-bay

 

[throbscottle]

Hmmm, Okaaayyy. So, are there non-phosphor ones out there?

 

[EinarA]

Not that I've ever heard. As far as I know all LEDs emit light of a single wavelength. The phosphor is needed to create a wider spectrum to simulate white. But I'm not a semiconductor physicist. Another thing that happens is that the LEDs themselves put out less light as they age.

 

[audioguru]

White can be made from a certain mixture of Red, Green and Blue lights or LEDs. But LEDs wear out.

I still have a name brand American clock radio. Its red LED 7-segment display has been lit (lighted?) every day for 30 years and now cannot be seen in daylight.

 

[throbscottle]

Pity. I suppose the thing is to just try to get high quality replacements. I didn't know they wear out.

AG - that is good service life there!

Thanks folks

 

[throbscottle]

I wonder if it's worth getting 4 wire rgb led's for the magnifier? The ability to colour-tune the thing might be quite useful!

 

[alec_t]

I can vouch for LEDs wearing out. A red LED on my old car's dashboard had faded to about half its original perceived intensity after being on ~ 8 years continuously (70k hours). Not so good as AG's LED-life. Perhaps I should have complained and asked for a free replacement .

 

[EinarA]

I also have a 30 year old LED clock, but it doesn't seem dimmer now. It has a high/low brightness switch that has always been on low, so maybe if you keep the current low they don't fade as much. (I think Ron tried to say this.) There is also no discernible difference between the segments as there would be if they had in fact faded a lot as some of the segments are on less often than others. ( I have seen this effect on other displays.)
I have also experimented with RGB LEDs and can say they are tricky to adjust. But the big problem is that the colors do not blend nicely; you just get splotches of red,green, and blue. Before ordering any parts you should do some research to see if anyone has solved this.

 

[throbscottle]

The lamp has been resolved somewhat - found it had been running on batteries instead of it's wall wart! Doh! Nevertheless, it's done maybe 50 hours service, and it doesn't seem quite as bright as when it was new. Will have to see what happens.

 

[dr pepper]

Well then that explains things.
Some white leds use phosphor and some use quantum dots that convert uv to white, I dontknow if these last longer or not, but they are newer technology so probably.
You'll probably get 1000's of hours before any significant drop in o/p.