Ben Okopnik wrote:
>
> I've actually done a lot of research on this in the recent past (within
> the last year) as a business proposition, and here's the take-home:
> top-quality, very expensive LEDs currently win out by a narrow margin
> over the top-end CFLs; medium-quality CFLs win out by a large margin
> over the medium-quality LEDs.
>
I would more or less agree with this except would say the margin of LEDs
over CFLs is more than "narrow" now, and would point out that expensive
is a relative term. For instance, the average Joe will pay around 5
dollars US minimum for a Rebel white LED (a state of the art
model)....OEM's pay only a fraction of that, and what is more the
amount of light per dollar is a lot greater with these high end LEDs
than with any others on the market. There are other considerations that
complicate things though such as the more powerful LEDs need a more
sophisticated 'driver' or power supply, thermal management issues become
critical, ect. and all that can add up in the bottom line quickly. Even
taking all these things into consideration, more light output power per
LED equals less cost to the consumer. And the newer top quality models
bring longer lifetimes which mean lower lifetime costs, and more
functionality which can also result in a better value.
> To expand on this, there are also LEDs currently in the testing stage -
> not yet in production - that are significantly more efficient than CFLs
> depending on the usage pattern [1] (not three times more efficient,
> however; that would require about 60% efficiency from the LEDs, and
> little beyond fireflies comes even close to that. :)
>
Here is some data I have gathered from various sources regarding light
output of several types of devices.
32 watt T8 fluorescent--85 to 95 lumens/watt
standard cool white fluorescent--60-65 lumens/watt
compact fluorescents--low 30's to low 60's lumens per watt, usually
48-60
T3 tubular halogen--20 lumens/watt
standard 100 watt incandescent--17 lumens/watt
incandescent night light bulb (7w)--6 lumens/watt
incandescent flashlight bulbs--dismal, less than 6 lumens/watt
Compare the above to the Lumiled white and colored K2 LED's
the white being rated at 140-175 lumens per watt!
(See; http://www.philipslumileds.com/products/luxeon/luxeonK2)
Not only that but since they waste far less light than the above
sources by putting the light right where it is needed the gain
is much better than the numbers would indicate.
It would seem just by these numbers that LEDs already outstrip CFLs in
efficiency by a noticeable margin. If we use a low efficiency model of
CFL and a high efficiency LED for comparison in fact we would see a
200-300% increase in light per watt, best case (for the LED anyhow)
comparison. Even a more moderate comparison is better than a 100% gain.
My experience backs this up. I have seen a LED strip light fixture
running at ten watts that FAR outshone a boat CFL fixture that West
Marine had that was running at about 13 watts (ten watts claimed)!
> Theoretically, LEDs that are currently in production compare favorably
> with CFLs for lighting purposes; both are quite efficient, with the LEDs
> winning out in a number of ways (no high start-up current; no usage
> pattern requirements; much higher shock resistance; much lower
> production cost, etc.) The problem with using them for lighting,
> however, has to do with three factors: luminous flux (amount of output),
> beam angle, and luminous intensity (which varies inversely with the beam
> angle.) The greatest majority of LEDs today do not produce a high-enough
> combination of LF and BA to satisfy the average consumer.
>
I agree with the last statement 100%. If you want LED lighting you must
use LEDs that are suitable for the application. They are out there, but
they do cost more, and the cheap fixtures that many buy do NOT use them.
Beam angle is not much of a problem with the high end LEDs. You can get
a very wide beam angle LED than attach cheap over the counter optics to
it to form 'almost' any angle you want. A notable exception is the
angles required to make up navigational light sectors. For that, you
need to make your own scheme.
It seems to me that the best solution for LED based general area boat
illumination is to make lights with very wide, very bright beams that
can be efficiently dimmed. That satisfies nearly all usage, and by
adding the ability of aiming the beams to avoid areas where you don't
want light (such as a sleeping spouse) or intensifying it where you do,
pretty much all bases are covered. Of course it is hard to find a single
fixture that will satisfy all needs and the field of LED boat lighting
is still young.
I note that the up front cost will always be higher for better
quality, be it efficiency or reliability or functionality, but OTOH that
cost continues to drop.
> Solutions to this range from producing higher intensity LEDs (e.g.,
> Nichia and others), through stacking a large number of LEDs for area
> coverage (LED panels - very expensive but work well), to optical
> solutions (e.g., taillights in new model cars) that spread and focus the
> beam. All of these are bearing fruit; none of them have yet achieved
> that magical combination of commonly-available AND cheap.
>
It has come to the point where you often do not actually need many LEDs
in an array to get very high intensity levels, even the new LED car
headlights use only a few very high power LEDs. (Some experimented with
just ONE extremely high power LED per fixture but lifetimes due to
thermal problems were too short it seems).
The over-riding issue now is thermal management. This is where the Rebel
LED 'shines', as it is by far the best thermaly designed LED on the
market today, needing far less heat sinking per lumen than any other LED.
The LEDs used in car tail lights are pretty much obsolete by the time
the car is in production, so using them for comparison purposes bias
things toward older technology that can pretty much easily be superseded
with newer models. It is best to start with a clean slate.
And again, as far as cost, the Lumiled K2 LED makes as much light for
less than four bucks as more than 70 of the worlds best LEDs of only a
few years back (Nichias 5mm white lamp style which were the reigning
champs in 2002) that cost over a dollar apiece. So while cost IS an
issue, the fact is that it is dropping at a rapid rate and it is now
*almost* at the point where the 'front end' cost is low enough to
compete favorably with other general illumination lighting devices.
Things were on track so that it looked to me that within three to five
years they would be competitive in that arena in the US for cost
(remember Wal-Marts fave Chinese and Koraean LEDs are not as efficient
and really efficient ones cost more), until the global slowdown anyway.
It will still happen, but maybe not quite as fast now. Even then,
inertia dictates it will take much longer for them to be widely adopted.
Look how long household CFLs have taken, even with a Government mandate.
-Ken
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