In article ,
robgraham writes:
As usual, we do get nothing for nothing and it's all very well the
pundits telling us that the next generation of lighting will be the
ultimate solution in terms of cost and efficiency but as is all too
common the whole picture has not been presented.

The big problem with LED light output figures are that they are
quoted at a junction temperature of 25C. Above this, light output
drops significantly and the life of the LEDs drop significantly.
To achieve a junction temperature of 25C in something the size of
a 100W GLS lamp with comparable light output and passive cooling,
you'd probably have to be operating it at something like -100C
ambient in a well ventilated fitting. That pretty much kills LED
lighting in the retrofit replacement lamp marketplace. Once you
go up to larger light sources which stand some chance of dissipating
the heat and remaining cooler, you're in the territory of fluorescent
tubes, and LEDs can't compete there.

I think they'll retain the niche they now have, but unless there's
a breakthrough that allows operation at much higher temperatures
or very much higher efficiency (which probably implies phosphor-less
operation), I don't see them replacing compact light sources such
as GU10 and MR16 halogens. Commercially, these have already been
replaced with metal halide anyway, and that will probably move into
the domestic market soon.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]