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Old October 3rd 19, 02:29 PM posted to uk.d-i-y,alt.home.repair,alt.sci.physics,alt.electronics
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Default Why do LEDs generate heat?

Why do LEDs generate heat? I want a technical answer not "because they're inefficient". And will we ever make them more efficient?

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Old October 3rd 19, 02:37 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not "because they're inefficient".


That is the technical answer just lioke why does a wire get hot when curremnt passes through it.

And will we ever make them more efficient?


Probably.


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Old October 3rd 19, 02:45 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thu, 03 Oct 2019 14:37:34 +0100, whisky-dave wrote:

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not "because they're inefficient".


That is the technical answer just lioke why does a wire get hot when curremnt passes through it.


No, the technical answer would explain what part of it has resistance and if it can be overcome by using different materials. And are you sure it's even resistance? It could be some photons are reabsorbed before they escape the LED, generating heat.

And will we ever make them more efficient?


Probably.

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Old October 3rd 19, 02:49 PM posted to uk.d-i-y,alt.home.repair,alt.sci.physics,alt.electronics
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Default Why do LEDs generate heat?

On Thu, 03 Oct 2019 14:29:30 +0100, Commander Kinsey wrote:

Why do LEDs generate heat? I want a technical answer not "because they're inefficient". And will we ever make them more efficient?


I got useful answers from Quora:

"LEDs are ever more and more efficient. In the last 40 years, tremendous strides have been made. They generate heat because they are conducting electricity through semiconductors. Unlike metals which have very little resistance to electric currents, semiconductors offer more resistance. Not as much as true nonmetals, but still more than metals. It is the resistance of the semiconductor layers, both N and P, and the resistance of the junction itself, that generate the heat."

"Every electronic device is less than 100 percent efficient. On a low level, it is due to the law of probability, or as the physicists call it, entropy. The odds of all those electrons conveying their energy into photons is very low. Some are always making random transitions, generating heat instead of light."
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Old October 3rd 19, 02:58 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thursday, 3 October 2019 14:45:38 UTC+1, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:37:34 +0100, whisky-dave wrote:

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not "because they're inefficient".


That is the technical answer just like why does a wire get hot when curremnt passes through it.


No, the technical answer would explain what part of it has resistance.


Every conductor has resistance apart from perhaps a superconductor.
yuo also have theb curent passing from one type of conductor to another.
One of those conductors will convert the energy to light and heat.
They won;t create much IR or UV because the material chosen was chosen because it emits the required wavelengh of light and not much eles.

and if it can be overcome by using different materials.


No they have been trying for years and until someone can come up with a magic substance that has zero resistance that is.

And are you sure it's even resistance? It could be some photons are reabsorbed before they escape the LED, generating heat.


No that would be IR 'heat' , and why would photons be re-absorbed anyway ?



And will we ever make them more efficient?


Probably.




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Old October 3rd 19, 03:01 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thursday, 3 October 2019 14:49:47 UTC+1, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:29:30 +0100, Commander Kinsey wrote:

Why do LEDs generate heat? I want a technical answer not "because they're inefficient". And will we ever make them more efficient?


I got useful answers from Quora:

"LEDs are ever more and more efficient. In the last 40 years, tremendous strides have been made. They generate heat because they are conducting electricity through semiconductors. Unlike metals which have very little resistance to electric currents, semiconductors offer more resistance. Not as much as true nonmetals, but still more than metals. It is the resistance of the semiconductor layers, both N and P, and the resistance of the junction itself, that generate the heat."


pretty much what I"ve just said. without Quora.



"Every electronic device is less than 100 percent efficient. On a low level, it is due to the law of probability, or as the physicists call it, entropy. The odds of all those electrons conveying their energy into photons is very low. Some are always making random transitions, generating heat instead of light."


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Old October 3rd 19, 03:08 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thu, 03 Oct 2019 15:01:34 +0100, whisky-dave wrote:

On Thursday, 3 October 2019 14:49:47 UTC+1, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:29:30 +0100, Commander Kinsey wrote:

Why do LEDs generate heat? I want a technical answer not "because they're inefficient". And will we ever make them more efficient?


I got useful answers from Quora:

"LEDs are ever more and more efficient. In the last 40 years, tremendous strides have been made. They generate heat because they are conducting electricity through semiconductors. Unlike metals which have very little resistance to electric currents, semiconductors offer more resistance. Not as much as true nonmetals, but still more than metals. It is the resistance of the semiconductor layers, both N and P, and the resistance of the junction itself, that generate the heat."


pretty much what I"ve just said. without Quora.


The answers I pasted were far more detailed. I did say I wanted a technical answer.

"Every electronic device is less than 100 percent efficient. On a low level, it is due to the law of probability, or as the physicists call it, entropy. The odds of all those electrons conveying their energy into photons is very low. Some are always making random transitions, generating heat instead of light."


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Old October 3rd 19, 03:08 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On 03/10/2019 14:45, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:37:34 +0100, whisky-dave
wrote:

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey* wrote:
Why do LEDs generate heat? I want a technical answer not "because
they're inefficient".


That is the technical answer just lioke why does a wire get hot when
curremnt passes through it.


No, the technical answer would explain what part of it has resistance
and if it can be overcome by using different materials.* And are you


It is resistance in the sense that there is some frictional losses to
the movement of current in the crystal lattice. Early LEDs you could
bump up the quantum efficiency by stiffening it - immersing in LN2
worked a few times before thermal cycling killed it stone dead.

sure it's even resistance?* It could be some photons are reabsorbed
before they escape the LED, generating heat.


White LEDs rely on a yellow phosphor absorbing and re-emitting blue
photons to make a perceived white light. Coloured LEDs typically have a
forward voltage related to the energy of photon that they emit.

There is a hit for doing that that limits ultimate efficiency to
something like 40% of power consumed out as useful light.

For comparison a tungsten light bulb is only about 2% efficient at
making visible light.

And will we ever make them more efficient?


Probably.


Quantum efficiency and efficacy of LEDs has been improving with time.
Cree have production models at 100Lm/W another factor of 2.5
improvement is theoretically possible and the odd sample has been made
but the problems of making such a device in production quantities isn't
cost effective at present. Cost per lumen and total flux graphs show how
much improvement there has been since the first LED indicators in 1970.

https://en.wikipedia.org/wiki/Light-...bre akthrough

--
Regards,
Martin Brown
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Old October 3rd 19, 03:10 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thu, 03 Oct 2019 14:58:46 +0100, whisky-dave wrote:

On Thursday, 3 October 2019 14:45:38 UTC+1, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:37:34 +0100, whisky-dave wrote:

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not "because they're inefficient".

That is the technical answer just like why does a wire get hot when curremnt passes through it.


No, the technical answer would explain what part of it has resistance.


Every conductor has resistance apart from perhaps a superconductor.
yuo also have theb curent passing from one type of conductor to another.


I assumed that the layers were so thin, resistance should be minimal. I guess transistors are the same and they get hot. Semiconductors probably have quite a high resistance?

One of those conductors will convert the energy to light and heat.
They won;t create much IR or UV because the material chosen was chosen because it emits the required wavelengh of light and not much eles.

and if it can be overcome by using different materials.


No they have been trying for years and until someone can come up with a magic substance that has zero resistance that is.


Well they've certainly improved the efficiency over the years. The question is how far can they get without using them at absolute zero? Or perhaps even a completely different way of generating light?

And are you sure it's even resistance? It could be some photons are reabsorbed before they escape the LED, generating heat.


No that would be IR 'heat' , and why would photons be re-absorbed anyway ?


Because they might not come out of the LED into the room, but hit another part of it internally.
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Old October 3rd 19, 03:16 PM posted to uk.d-i-y
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Default Why do LEDs generate heat?

On Thu, 03 Oct 2019 15:08:43 +0100, Martin Brown wrote:

On 03/10/2019 14:45, Commander Kinsey wrote:
On Thu, 03 Oct 2019 14:37:34 +0100, whisky-dave
wrote:

On Thursday, 3 October 2019 14:29:30 UTC+1, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not "because
they're inefficient".

That is the technical answer just lioke why does a wire get hot when
curremnt passes through it.


No, the technical answer would explain what part of it has resistance
and if it can be overcome by using different materials. And are you


It is resistance in the sense that there is some frictional losses to
the movement of current in the crystal lattice. Early LEDs you could
bump up the quantum efficiency by stiffening it - immersing in LN2
worked a few times before thermal cycling killed it stone dead.

sure it's even resistance? It could be some photons are reabsorbed
before they escape the LED, generating heat.


White LEDs rely on a yellow phosphor absorbing and re-emitting blue
photons to make a perceived white light. Coloured LEDs typically have a
forward voltage related to the energy of photon that they emit.

There is a hit for doing that that limits ultimate efficiency to
something like 40% of power consumed out as useful light.


I didn't realise that, I thought white LEDs were designed to directly emit a handful of different visible light wavelengths to make white. Is there a reason this can't be done? An LED can make anything in the visible light spectrum, so surely a mixture of them would be more efficient than using phosphors? There could even be seperate LEDs within the housing, like growlamps which have visible, IR, and UV LEDs.

For comparison a tungsten light bulb is only about 2% efficient at
making visible light.

And will we ever make them more efficient?

Probably.


Quantum efficiency and efficacy of LEDs has been improving with time.
Cree have production models at 100Lm/W another factor of 2.5
improvement is theoretically possible and the odd sample has been made
but the problems of making such a device in production quantities isn't
cost effective at present. Cost per lumen and total flux graphs show how
much improvement there has been since the first LED indicators in 1970.

https://en.wikipedia.org/wiki/Light-...bre akthrough


That graph looks very promising.


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