Papers pertinent to white LED lifetimes.

It's worth noting that the "100,000 hour LED lifetime" often 
quoted for LED products is usually grossly untrue.

Another useful point to note is that lifetime will be 
decreased at constant current as junction temperature rises 
OR at constant junction temperature as current rises. So 
both a low current and low Tj are desirable for best 
lifetimes.
It's also worth noting that encapsulation material can make 
a vast difference to lifetimes. All epoxies are far from 
equal in such applications and silicones (no great surprise) 
tend to be superior due both to their superior UV handling 
(due to Si-O-Si bonds being higher energy than epoxy C-C), 
higher temperature ratings and gentler action on bond wires 
etc due to their softer and more flexible nature.

Needless to say, to have any chance of achieving rated 
lifetimes LEDs need to be driven in a constant current mode 
at rated current or less. The common mass market practice of 
hard paralleling multiple LEDs is an invitaiton to vastly 
unbalanced performance and very early failures.


        Russell

_______________________

Superb slideshow on white LED lifetime issues
UKNC Jan 2007.

        http://www.uknc.org/papers/Jan07/Humphreys.pdf

Excellent lumileds paper on "Understanding Power LED 
lifetime analysis".
The dread Waloddi Weibull takes a bow.

        http://www.lumileds.com/pdfs/WP12.pdf

Good general LED lifetime and related intro
Low technical level.

        http://www.ledsales.com.au/cart.php?page=led_faqs

Philips ra ra but in passing useful news article on lifetime 
prediction tools

        http://www.eetimes.com/press_releases/bizwire/showPressRelease.jhtml?articleID=603418&CompanyId=2

TOC for a LED manufacturing technologies report.
Full version will cost you $US4990 or more.
TOC alone has some value.

        http://www.electronics.ca/reports/technology/led_manufacturing.html

 Already date but still useful 2004 intro to "How white LEDs 
work".

        http://www.compoundsemi.com/documents/articles/news/4706.html




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