Philips Lumileds have just published a White Paper, ‘Evaluating the Lifetime Behaviour of LED Systems’ Although aimed at LED product manufacturers it provides useful insight and information of designers using LED systems.

The paper uses gambling analogies in a disturbingly effective way to explain how to realistically determine system life for LED strings. I am a bit at sea with the details of the statistical methods used but this does point the way to assessing realistic system and product life and edges us further and further away from the claims of “50,000 hour” life of LED based products and systems.

As lighting designers this pushes us more towards needing a degree in Maths to be able to assess lifetimes for systems, having said that our brief relief from heavy maths for lighting calculations thanks to DIALux , RELUX etc. is being broken down by understanding new lighting metrics such as LENI, more about that in another post!

The paper does quite effectively promote Luxeon Rebel LEDs but you can easily read beyond this to the real meat of the paper. Another interesting side comment is the recommendation that all LED systems should be current driven. This is actually a significant issue that has recently caused us some problems. Basically a lot of lighting manufacturers are producing voltage driven systems. This is not at all obvious from catalogue data and is not necessarily understood by less technical sales people so yet another pitfall for lighting designers in specifying systems!

Good luck!

Kevan Shaw