Help understanding LED lumen maintenance info - Page 1
Forum section: electronics / projects

author: eecook
author_rank: Regular Contributor
timestamp: August 17, 2017, 05:38:29 pm
content: Hi All,I have been going thru several LED datasheets as I am trying to select a suitable part for my design. I quickly realized realiability/durability data is non standard, which I in fact verified after googling around a bit. At this point I stumble upon this reliability info for part CLU028-1201C4-303H5K2 on Digikey. I get the following data:I am not sure what this data means as far as lumen maintenance goes.My way of interpreting this is the following:1. Continuous operation test, Tj will be way cooler in my application. So I can conclude that it will take more than 1000hs to get to "L85".2. Same as 1) for storage temp.3. Not sure what to conclude from this one.4. Thermal cycling test seems like the only test I can use. It is running at an average 30C which is realistic, but incorporates some unrealistic cycling (As far as my application goes) and only adds up to 100 cycles x 1hr/cycle = 100hs!So taking worst and best case scenarios I could expect my LEDs lumen maintenance to be somwhere between 100-1000hs (L85)?That can't be right!Where am I getting this wrong?The only idea I have left is extrapolating the "Continuous Operation" or "Moisture Proof" info to some other temperature using the Arrhenius equation (same one used for AE caps life estimation)Any ideas?NOTE: My application is simple house illumination.

author: StillTrying
author_rank: Super Contributor
timestamp: August 17, 2017, 07:01:50 pm
content: I don't think it's saying they fail at 1000 hours, just that they where tested for 1000 hours and didn't!

author: eecook
author_rank: Regular Contributor
timestamp: August 17, 2017, 07:37:35 pm
content: I am not talkin about failure, I am talking about lumen depreciation

author: DaJMasta
author_rank: Super Contributor
timestamp: August 17, 2017, 07:52:04 pm
content: So you're looking for an average time until it hits only 85% of its original brightness?The way I read that bottom bit is that their test results are a pass/fail average over many test units, where the failure condition is that at the end of the test, the lumen output is < 85% of the initial output. I don't actually see any reliability test data in the info you have provided - I'd expect the data to be something like a percentage or some decimal number in 1000 units or something.

author: georges80
author_rank: Frequent Contributor
timestamp: August 17, 2017, 08:07:35 pm
content: The datasheet only talks about failure criteria. There is no information in the datasheet that addresses lumen maintenance which isn't too surprising since it will be dependent on drive current and average operating temperature over the life of the product.You would need to contact citizen to get that information if it is really of concern. If this is for a personal project, just make sure you provide a good thermal path to minimise junction temperature, provide good current regulated drive to the array and it should be good to go for 10's or 100's of thousands of hours (versus some ebay LED)...cheers,george.

author: jmelson
author_rank: Super Contributor
timestamp: August 17, 2017, 08:37:28 pm
content: Some companies, like Cree, give pretty extensive data for the loss of output over time, with curves, etc. to compute what you will get given current and temperature.Jon