Re: Fluorescent heating
- From: don@xxxxxxxxxxxxxx (Don Klipstein)
- Date: Tue, 30 Dec 2008 00:38:10 +0000 (UTC)
In article <kg4hl49vaeiq5gh67ogvpo89avlfmerkh2@xxxxxxx>, JosephKK wrote:
On Fri, 26 Dec 2008 18:07:46 +0100, Ken <ken_3@xxxxxxxxx> wrote:
On Fri, 26 Dec 2008 11:35:36 -0500, "Paul E. Schoen" <pstech@xxxxxxxxx>
wrote:
A flourescent light is pretty much the same. They consume less
power, dissapate less heat, but still most of the energy consumed
is dissapated in the form of heat. It doesn't take very much energy
to radiate light - we just can't do it efficiently.
Incandescent is horribly inefficient - but it's cheap and we don't
care that we are wasting so much energy. Flourescent lights
take a circuituous route to emit light in the visible spectrum - not
very efficient at all, but much better then incadescent.
LEDs are much more efficient, but still some of the energy goes to
heat - I'm not sure what the ratio is. Visible light itself is
not very much energy. It all goes to heat.
I wonder whether LED's are more efficient than the good old
tube fluorescent lamps.
Not yet.
Some white LEDs are pushing 160 lumen/watt now - at least if you believe
Cree's press releases (they claimed 130 lumen/watt about 2 years ago).
http://news.moneycentral.msn.com/ticker/article.aspx?Feed=PZ&Date=20081119&ID=9391712&Symbol=US:CREE
LEDs capable of 90+ lumens/watt are starting to appear in consumer LED
lighting some of the claims made are a bit optimistic eg
http://www.arraylighting.com/Story/index.html
But there are very few fluorescents that can work as efficiently as
that.
My gut feeling is they still have some distance to go to get there.
Yes.
Consumer mass produced ones still lag a bit behind the best prototypes.
Although for some coloured light sources like traffic lights and
indicators LEDs can still come out ahead.
In answer to the original question a low pressure sodium lamp with the
InO coating etched off the glass envelope would emit a pretty strong IR
line source at very high efficiency (with a suitable low pass filter to
stop the obvious visible yellow sodium D line escaping).
High Lumen/watt is not all we need.
The color temperature (Kelvin) and Color Rendering Index (CRI)
are very important factors.
Today I can't buy LEDs that have better efficiency than
fluorescents with 2700K and >CRI90 for my home lighting.
The other important factors are longevity (LEDs are typically 50,000+ hr),
ability to work in cold environments, and the true environmental costs of
manufacturing and disposal. I think there are white LEDs with a wide range
of color temperature, and those that use RGB can be adjusted to whatever
you need. Earlier white LEDs used a phosphor coating that made them less
efficient, while newer ones I think use the light output directly, perhaps
from a cluster of component colors.
Also the power conversion from line voltage to LED current can approach
97%, while I doubt that most CFLs are much better than 90%, but I'm just
guessing by how hot the base of CFLs are. I think there has been a major
investment in CFL technology and manufacturing that causes resistance to
switching over to LEDs, and the fact that CFLs need more frequent
replacement is also a plus for those who want a continuing business.
Paul
This is my favorite http://tekniken.se/misc/philips_tld36w-92.jpg
This tube is 20 years old now and still going strong.
I can't find any LED that have this light quality. 2700K CRI95
I challenge both the color temperature claim and the CRI claim, and
especially the combination. 2700 K would be rather yellow-orange
colored. Standard incandescent are around 3200 K color temperature
and do not have over 90 CRI.
http://www.betterphoto.com/article.asp?id=24
http://www.techmind.org/colour/coltemp.html
http://en.wikipedia.org/wiki/Black_body
Most household incandescents have color temp. 2700-2900 K, and have CRI
of 100 by definition. The 100 watt 750 hour 120V A19 has a color temp. of
2865 K according to Kodak.
http://www.kodak.com/US/plugins/acrobat/en/motion/support/h2/h2fltrs.pdf
(Though their figures for daylight sources appear a bit high to me. They
say 5800K for direct sunlight in midsummer - and the color of the sun's
light would have to be not yellowed at all by the atmosphere for that to
be true. The color temp. of sunlight in outer space is a bit less. I
suspect they are stating effective figures for usual films, including the
ability of the film to react to UV.)
- Don Klipstein (don@xxxxxxxxx)
.
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