Re: Odd Question: are LEDs more efficient than incandescents?

[Brandon Stafford <thehag@Stanford.EDU>]

Hello Mr. Stophilis,

	As Mr. Fixit says, how are you?

	I found the excerpt below at:
http://www.pioneernet.net/optoeng/LED_FAQ.html#Q7

	The answer to your question appears to be: No, they are pretty
much the same, but because of the brightness lost in filtering for color,
the LEDs are better for taillights and the like.
	Also, I dug up some data on incandescents and LEDs, and
they came in at 15.4 lumens/watt and 14.8 lumens/watt respectively.
Fluorescents are up around 40 lumens/watt. Anyway, here is the excerpt:

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Are LEDs more efficient than other light sources such as incandescent
and fluorescent types?
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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.

Have a good day,
Brandon Stafford
Palo Alto, CA