How to detremine the lifetime of a LED

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    Led Lifetime
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Discussion Overview

The discussion revolves around determining the lifetime of LEDs, exploring methods for testing and understanding the factors that contribute to their degradation. Participants discuss theoretical and practical approaches to lifetime testing, including temperature effects and failure mechanisms.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants note that theoretically, LEDs can last for 100,000 hours but question how to verify this claim.
  • It is suggested that lifetime testing is typically conducted at elevated temperatures to accelerate degradation and estimate performance at room temperature.
  • One participant humorously proposes simply waiting for an LED to fail as a method of testing.
  • Another participant emphasizes the importance of understanding the relationship between temperature and lifetime, suggesting that it may not be linear and could be exponential.
  • There is mention of the "bathtub curve" or Weibull distribution in relation to product failure rates, indicating that lifetime ratings are statistical measures.
  • Some participants raise questions about the physical reasons for intensity degradation in LEDs, citing potential causes such as dopants migrating, corrosion of bond wires, and chemical changes in encapsulating materials.
  • One participant points out that some manufacturers define LED lifetime based on when the output drops to a certain percentage of the initial light output.

Areas of Agreement / Disagreement

Participants express a range of views on the methods for determining LED lifetime and the factors influencing degradation. There is no consensus on a single approach or understanding of the lifetime definition.

Contextual Notes

Participants acknowledge that lifetime testing may involve various assumptions and that results can vary based on the specific conditions and devices tested. The relationship between temperature and lifetime remains uncertain, with suggestions of both linear and exponential models.

Who May Find This Useful

This discussion may be of interest to those involved in LED manufacturing, reliability testing, or anyone seeking to understand the factors affecting LED performance and longevity.

shen3
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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?
 
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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.
 
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.
 
CraigD said:
Just turn it on and wait for it to fail.
That's the problem with the perpetual motion machine invented by my great-great-great grandfather, we are still waiting for it to stop!
 
mgb_phys said:
That's the problem with the perpetual motion machine invented by my great-great-great grandfather, we are still waiting for it to stop!

:smile::smile:


This article may give you some hints:
http://www.netl.doe.gov/ssl/PDFs/lifetimeWhiteLEDs_aug16_r1.pdf
 
mgb_phys said:
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.

Then how do i calculate what the lifetime would be at room temperaure?
 
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.
 
mgb_phys said:
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.

..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?
 
Dario78 said:
..or, you can check for a producer site, example: osram, lumileds. They surely have all this info.
The OP wanted to know if the specs were true

I have a question, what is the physically reason for the intensity degradation of a LED?
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
shen3 said:
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?

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

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