The problem with using white LED's for lights is they don't last very long.
It's common for white LED's to get dim in just a few weeks of continuous use.
I know they always say that LED's last a long time, thousands of hours usually,
but that's a lie. Red and green LED's usually have a long life but white and
blue ones do not. I've been struggling with this problem myself and I've tried
4 different kinds of white LED lamps but they all go dim in just 2-3 weeks.
Some get really dark sooner than others but they all tend to turn a bluish
purple and get dark and keep getting darker the longer they are on.
The only solution I've found is to get new LED's and replace the old ones,
however, the new led's don't last any longer than the original ones did
in the case of 5mm LED's.
One solution I'm considering is switching to a new type of surface mount
LED that is much brighter and also is supposed to have a longer life,
the LUXEON I 1 Watt LED from Philips that is used in high power flashlights.
They are relatively cheap since being replaced by the more powerful LUXEON 3 LED, $2.95 each from Tek-Tite.com,
http://www.tek-tite.com/src/product_info.php?id=2985.
The data sheet is available here,
http://www.luxeon.com/pdfs/DS25.pdfThe LUXEON I LED's are very small and put out a lot of light and are rated
by Philips to put out 70% of lumens at 50,000 hrs but I don't know if that's
really true or not, at least not yet. They are not
directly interchangeable with the older 5mm LED's since they use 350ma
of current, not 20ma and get hot so they have to be glued to a heatsink for
cooling. For these reasons they wouldn't make good replacements but need to
have a new lamp designed to use them. I'm thinking of using a switching supply
with 12-15V. DC output to power 3-4 LUXEONs in series.
I'd be interested in knowing if anyone has any better ideas or if you
have run across any white 5mm LED's that actually last very long that
would be good for replacements in dim LED lamps. Thanks.