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Nanotube are more efficient IR source than LEDs

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Robert

Jan 1, 1970
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Physicists have discovered a way for carbon nanotubes to emit IR light (in
the optical fiber wavelengths) more efficient than LEDs. Perhaps they can
get them to laze.

http://physicsweb.org/articles/news/9/11/12/1
" ...3 milliamp current was able to produce about 105 times more photon flux
than a large area LED."

Robert
 
K

Kryten

Jan 1, 1970
0
http://physicsweb.org/articles/news/9/11/12/1
" ...3 milliamp current was able to produce about
105 times more photon flux > than a large area LED."

The article actually says 10^5, i.e. 100,000 times more flux.

I find that a bit hard to believe, if they mean they get that much light for
the same current. That suggests the LED is 10^-5 the efficiency, and I
thought LED quantum efficiencies were in the tens of percent.

http://www.google.co.uk/search?hl=en&q=led+"quantum+efficiency"&meta=

Do they actually mean the device gave 10^5 times
more light per surface area, rather than solid angle?
 
I

Ian Stirling

Jan 1, 1970
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Kryten said:
The article actually says 10^5, i.e. 100,000 times more flux.

I find that a bit hard to believe, if they mean they get that much light for
the same current. That suggests the LED is 10^-5 the efficiency, and I
thought LED quantum efficiencies were in the tens of percent.

http://www.google.co.uk/search?hl=en&q=led+"quantum+efficiency"&meta=

Do they actually mean the device gave 10^5 times
more light per surface area, rather than solid angle?

Pretty much the same thing isn't it?
 
K

Kryten

Jan 1, 1970
0
Ian Stirling said:
Pretty much the same thing isn't it?

No, not at all.

Two small devices might put out the same amount of light into a cone shape
solid angle.

One might be an LED of about 1 mm^2 of light emitting area.

The second might have 10^-5 mm^2, e.g. a 3.16 micron square.
 
I

Ian Stirling

Jan 1, 1970
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Kryten said:
No, not at all.

Two small devices might put out the same amount of light into a cone shape
solid angle.

One might be an LED of about 1 mm^2 of light emitting area.

The second might have 10^-5 mm^2, e.g. a 3.16 micron square.

I should have been clearer - if you've got a size constraint - then for a
given lens size, decreasing source size means higher solid angle output for
a given power.

(until diffraction comes into play)
 
K

Kryten

Jan 1, 1970
0
Ian Stirling said:
I should have been clearer - if you've got a size constraint - then for a
given lens size, decreasing source size means higher solid angle output
for
a given power.

I don't understand that sentence either.

If you have the same amount of light power flowing into the same solid
angle, you have the same luminous flux.

And I'm still no clearer as to what the web page meant by that 10^5 factor.

They don't make any mention of lenses.
 
I

Ian Stirling

Jan 1, 1970
0
Kryten said:
I don't understand that sentence either.

If you have the same amount of light power flowing into the same solid
angle, you have the same luminous flux.

And I'm still no clearer as to what the web page meant by that 10^5 factor.

They don't make any mention of lenses.

I should have been even clearer.

Take a light source in a 5mm LED conventional package emitting 100mW IR.

Now.
If you have a 1mm source, you're going to get (about) a 15 degree beam.
Pretty much nothing other than throwing light away can get much better
than this.
This gets you about 1.6W/steradian.

If you have a .01mm source, you're in a different ballpark.
With perhaps an extra reflector, you can now get a .15 degree beam, in
the same package.
This is about 16Kw/steradian.
There is the same amount of light coming out of both - it's just that the
spot pattern of the nanotube based one at 1m will be akin to the LED based
one at 1cm.
 
K

Kryten

Jan 1, 1970
0
If you have a .01mm source, you're in a different ballpark.
With perhaps an extra reflector, you can now get a .15 degree beam, in
the same package.
This is about 16Kw/steradian.

Okay so width of the light source makes for more off-ideal-axis light.

But I suspect that most applications will need the same sort of beam width
as LEDs have now. One has to be able to read equipment at moderate angles.
 
I

Ian Stirling

Jan 1, 1970
0
Kryten said:
Okay so width of the light source makes for more off-ideal-axis light.

But I suspect that most applications will need the same sort of beam width
as LEDs have now. One has to be able to read equipment at moderate angles.

Basically, yes.
Smaller light source means more flexibility.
You can use simple optics, rather than complex ones, in some cases.
If you're just doing flood illumination, then there is no benefit.
Even for things like conventional LEDs, you can more closely specify the
beam pattern.
For example, to eliminate the hot-spot in the middle, and make the light
output constant to a sharp cutoff.
 
R

Rich, Under the Affluence

Jan 1, 1970
0
The article actually says 10^5, i.e. 100,000 times more flux.

I find that a bit hard to believe, if they mean they get that much light for
the same current. That suggests the LED is 10^-5 the efficiency, and I
thought LED quantum efficiencies were in the tens of percent.

http://www.google.co.uk/search?hl=en&q=led+"quantum+efficiency"&meta=

Do they actually mean the device gave 10^5 times
more light per surface area, rather than solid angle?

I think it's just merely journalistic incompetence. A photon flux
of 10^5 of a large area LED would burn the house down.

I was kind of hoping for something like nanotube-sized nanometer-wave
klystron lasers, and feedhorns -

Maybe even something like an array of these nanotubes mounted orthogonally
on one of those magical graphittine sheets, to put a 100 MW laser in a
pistol... But we need better battery technology.

Thansk,
Rich
 
K

Kryten

Jan 1, 1970
0
Rich said:
I think it's just merely journalistic incompetence. A photon flux
of 10^5 of a large area LED would burn the house down.

Yeah, I thought that too.

When someone proposed using LEDs for traffic lights, someone else pointed
out that there wasn't really enough gallium produced to satisfy that market.
It is only produced (as a by product of the aluminium refining industry
IIRC) in the order of tonnes per year. Enough for the many existing
applications needing tiny indicators.

Carbon nanotubes are currently more expensive than gold, but if they are
10^5 times more light per mass used then they can still be more cost
effective. Gold itself is sparingly used in electronics packaging.
Maybe even something like an array of these nanotubes mounted orthogonally
on one of those magical graphittine sheets, to put a 100 MW laser in a
pistol... But we need better battery technology.

I have a vision of a Far Side cartoon:

"Yoo-hoo, Mister Froggatt!
My science fair project is ready!
Yeah, I'm talking to you, squidface!"

In the original cartoon it was a huge killer robot, but a Flash Gordon laser
pistol would do just as well...
 
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