[VAC] Re: LEDs

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

David,
 From the pioneer.net link:
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7. Are LEDs more efficient than other light sources such as incandescent
and fluorescent types?

LEDs are used more and more as incandescent light replacements. Their
are at least 4 possible advantages to
using LEDs compared to incandescent sources: a) longer lifetime, i.e.,
years rather than months of service, b)
power savings in some applications (more on this later), c) reduced heat
output in some applications, and d)
deep saturated hue (color) of output without filters.

Does this mean that LEDs are generally more efficient, that is, can they
be used to save power? With the
current state of the art, incandescent bulbs actually put our more
visible light per watt than most LEDs. So, if you
want white light or if you don't care about color of illumination,
incandescents are somewhat more efficient than
any combination of LEDs, and they remain more efficient than the newest
'white LEDs'. However, if you want
single color illumination, LEDs can be much more efficient, since, in
that case, much of the light output of the
incandescent source is absorbed by a filtering system. If we include
fluorescent fixtures, here is the general
picture of light source efficiency:

1) As of today, fluorescent fixtures remain the clear winner in terms of
output in lumens/watt. Halogen
incandescents are second. LEDs are third.

2) LEDs win the race if what you want is light of a single color
available from efficient LEDs. The losses involved
in filtering fluorescents and incandescents are such that LEDs win out
here. Examples include stoplights and
auto taillights.

3) LEDs provide the longest lifetime by far.

4) If your supply is some low DC voltage, driving circuits for LEDs are
extremely simple and cheap compared to
same for fluorescents.

5) White LEDs, although they do not presently provide as many
lumens/watt as incandescent bulbs, can be
useful because of the long life and low heat output.

Don Klipstein has done some lumen efficiency tests of LEDs. See the
Links section.

For reference, fluorescent fixtures put out about 30 lumens per watt.
Incandescent bulbs put out about 8 lumens
per watt.

In summary, if I were equipping a remote cabin with lighting, I'd be
using low voltage fluorescent fixtures at this
point in time.
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                                     <<Jim>>