# How to detremine the lifetime of a LED

1. Aug 8, 2007

### shen3

Theoratically a LED can last for 100,000 hours, but how can i prove that this is true? I've found out that the malfunction of a LED is caused by the degradation of the active region in it, but how can i determine when it is going to malfunction?

2. Aug 8, 2007

### mgb_phys

Life time testing is ussually done at higher temperatures.
You measure the life of a sample of parts at a number of higher than normal temperatures, you determine the function relating the lifetime to temperature and use it to calculate what the lifetime would be at room temperaure.

3. Aug 8, 2007

### CraigD

Just turn it on and wait for it to fail.

CraigD, AMInstP
www.cymek.com

P.S. you may want to bring a six pack.

4. Aug 8, 2007

### mgb_phys

That's the problem with the perpetual motion machine invented by my great-great-great grandfather, we are still waiting for it to stop!

5. Aug 8, 2007

6. Aug 8, 2007

### shen3

Then how do i calculate what the lifetime would be at room temperaure?

7. Aug 8, 2007

### mgb_phys

It depends on the function relating increased temperature and lifetime.
Eg. if you heat it to 100C and it last 50K hours, at 200C it lasts 20K you can plot a graph and see how long it would last at 20C.
Since you don't know that the relationship is linear, it is probably exponential, you would have to try a number of temperatures and see what shape the curve is.
You also have to do this for a number of devices to get an average behaviour and since you are running the device until it dies you only get one data point/device.

8. Mar 5, 2009

### Dario78

..or, you can check for a producer site, example: osram, lumileds. They surely have all this info.

I have a question, what is the physically reason for the intensity degradation of a LED?

9. Mar 5, 2009

### mgb_phys

The OP wanted to know if the specs were true

In theory - dopeants migrating out of the active region of the diode.
In practice - corrosion of the bond wires because of contaminants when it was made, chemical changes in the encapsualting plastic from the atmopshere, mechancially breaking the leads where the enter the plastic

10. Mar 5, 2009

### Andy Resnick

Lifetime testing is an interesting excersise. Typically, tests are performed at high temperatures to accelerate the process- to simulate the rapid passage of time. Also, products typically fail with a distribution known as the "bathtub curve" or Weibull chart:

http://en.wikipedia.org/wiki/Bathtub_curve

I forget what "lifetime of 100,000 hours" means in terms of MTBF or the Weibull chart, but it's a statistical measure, in the end. Your device may last longer or shorter.

11. Mar 5, 2009