> My guess as to why they are such a problem up here is that 
> they failed to
> take into account the over 55 degC ambient temperatures 
> inside a traffic
> light on a hot southern New England summer day. Add in all 
> the heat from the
> LEDs and it wouldn't surprise me if on some days it's well 
> over 80 degC in
> the light fixture.

Temperature is a great killer of LEDs. 10C increases can 
decrease lifetimes by 2 to 10 times depending on other 
factors. It doesn't take many 2X reductions to turn 100,000 
hours into disaster.

Philips / Luxeon / Lumiled have some excellent material 
available on lumen maintenance wrt temperature and mA drawn 
(essentially independent variables wrt effect despite 
usually being linked in practice by practical realities). eg 
you can get all combinations of IxTy and with differing 
results.



        Russell 

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