On Sat, 26 Jul 2003 11:39:53 +1000, "stu" may have
said:

The reason this works is that with a 3W conventional bulb, only about
one quarter of the energy used (at best, and generally much less) is
converted to light; with an LED, it's more on the order of two-thirds.

LEDs and quartz halogen have about the same lumens per Watt.

My lightmeters disagree. The comparison is more like 3 to 1 in favor
of the LED, compared to 6 to 1 for a conventional incandescent. This
is taking readings from several angles and averaging them together.
The data in one of the LED manufacturers' spec sheets suggests that my
estimates are off by a good bit in the halogen's favor, but I'll take
mine. They suggest a ratio that seems absurdly good; the halogen
would have to be using less than 4% of its energy consumption for
light production for the figures to be correct, and I think that's
probably a bit low.

Leds don't
needs as much focusing because most of the light comes out the front anyway.

Good news and bad news there; the beam *can't* be focused very well by
the use of additional reflector elements; the lens is all you have to
work with. This isn't optimal by any means.

So for a nice wide beam they work great. If you want a pencil beam you will
have trouble. and for the same sort of output you are talking lots of $.

Higher than incandescent initially, yes, but cheaper in the long run
in appropriate applications...and frankly, the site you mentioned is
horribly overpriced. I can get many of the same items locally for
about one third of those prices. Not everyone knows where the stuff
is available, so they probably get a lot of business from folks who
just don't know of any other source. Many of the local truck lines
have entirely swapped over to the LED tail and signal lamp assemblies
because the price for that long-life unit is about half the cost of
the conventional unit with two years' worth of maintenance added in.
See
MR-16 about halfway down the page only $80each(l think you would need about
4 of them to replace a 15W halogen)
http://www.theledlight.com/dcbulbs.html
and there figures are a little umm misleding (leading get it)
60mA at12vdc; 180 lumen; approximately 15 watts.
the 15watts they are talking about must be an incandescent bulb, which is a
little misleading being that it is a replacement of a halogen bulb

The lumens thing is also a bit difficult to make a comparison on; the
halogen bulb's output can, at this point, be utilized more efficiently
with reflectors that are already well understood and in production;
if, however, the lamp assembly is designed for the LED light source,
useful illumination levels which are comparable to those from halogen
bulbs can be achieved with less than one third of the power
consumption of halogen, just nowhere near as cheaply. On the other
hand, the LED assembly will be far more reliable. There are tradeoffs
everywhere.

some more interesting stuff on LEDs
http://www.theledlight.com/ledbulbs2.html

What they don't say (probably since I doubt that they know) is that
white LED units with a brightness adequate for automotive headlights
should be in mass production within the next 6 years, and should
appear in automobile and truck applications soon thereafter. There
are fundamental headlight design issues which must be addressed, and
it is considered unlikely that a DOT-approvable LED conversion for
existing headlamp bulbs will be marketed anytime soon, if ever. On
the plus side, it's not expected that the LED headlamps will be
anywhere near as hideously expensive as the high-frequency Xenon
strobe units that are currently available. They very well may reach
the level of standard equipment on low-end vehicles within 10 to 12
years. Since it's likely that the average LED headlight will outlast
the car that it's delivered with, they probably won't be something
that you'll find on the shelf at every parts store.


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