LED Light Emitters: Failure Mode?

An LED can grow dim if the input voltage is too high but I've never heard of one gradually dimming. This does not mean that it doesn't happen of course.

I have several of those little led keyring torches, and they do grow dimmer after a time compared with new ones even with brand new batteries.

Ron(UK)

Cheap Bastards, how dare they!

Gradual dimming is the normal way LEDs wear out. I thought it took years, though.

OK, Meat Wanka - we're in your parlour now. Let's see what Mr Big Mouth Show-Off's like when he's at home....

(I'll be in touch soon, sweedie.... ;-)

If you overdrive them it will happen much faster. I've done that a few times playing with LEDs.

Mike

Trevor Wilson

I have some blue Philips LED christmas lights that I was using as a night light. After they were on 24/7 for a year a number of LEDs had failed short circuit and the rest were 50-75% dimmer than new. I was very disappointed with them. Ordinary light bulbs last longer than that! They were either using cheap LEDs, or over driving them (or both). Looking directly into the dim LEDs I could see large dark areas on the dice. Andy Cuffe

snipped-for-privacy@gmail.com

I believe that some of these LED flashlights use drive electronics built into the head, to pulse the LEDs rather than DC drive them. It apparently produces a greater light density per amp, and helps to prolongue the life of the LEDs. It's possible that the one that has failed may have such electronics, and that's where the problem lies ??

Arfa

Don't do that! You'll put your eye out!

Maybe _that_ explains the "large dark areas ...."

Trevor Wilson

Yawn-------

It depends on the LED, some of them do in fact grow dim, the blue LEDs on my PC used to be identical, now the hard drive LED is considerably brighter than the power LED which is on far more. The phosphor coated LEDs dim even faster, white and pink LEDs are a phosphor over a blue chip.

I've had some too that got dim and flickered. I don't know the exact mechanism of failure.

I have some too that have bad LEDs, they flickered horribly as well, one set I modified with a rectifier and it was MUCH nicer looking then, it lasted a couple years but now has one dim flickering LED. My friend gave me some more sets which had not been modified and they have several more bad LEDs so it isn't the rectifier that did it. I'm not impressed with LED Christmas lights, they're just not there yet.

impressed

What you're saying suggests that the LEDs are simply connected across the power line in series, with the LEDs serving as their own rectifiers, so to speak. Glitches and spikes in the "reverse" direction aren't going to do the LEDs any good. Adding a rectifier presumably provides protection.

They probably were being overdriven. I have some blue LEDs that are on 24/7 now for 3 years without any sign of dimming. 2 of then make an excelent bathroom night light. I reccomend using a small transformer to step the voltage down to something close to the value they need. The LEDS will still have to draw there rated current if you use a resistor to drop the voltage from 120 you might as well use a light bulb instead of an LED.