9 ms·

MIT Researchers Produce Micro-Light that Outputs More Power Than Applied

48 points by jnand 14y ago

eck 14y ago
The title (and the first comment on the link) makes it sound like it's a perpetual motion machine, but as far as I can tell it's more like a tiny heat-pump: energy is conserved, entropy increases. Still kind of neat though.
- Cushman 14y ago
  Of course they didn't beat thermodynamics, but still, assuming they can scale the tech up to a useful power, it's a light that's also a cooling element. That'd be more than kind of neat, wouldn't it?
  - Ygg2 14y ago
    But where would you use light that cools? Fridge lights? House lighting in warm regions? Hmmm. On second thought it could have interesting applications depending how much it cools.
    - nagash 14y ago
      Data centers.
    - mbreese 14y ago
      Lighting is hot. I'd love to have lights that weren't also little heaters. Or, if the cooling effect is big enough - imagine solid state cooling on devices. Who needs a fan when you can have a little cooling light? I doubt that they'll be able to scale this up too much though, since it probably relies on an effect that only occurs below a certain threshold.
      - swombat 14y ago
        Most LEDs don't heat up that much... they're usually cool to the touch. I'd love a computer that glows brighter to release heat when it gets too hot, though :-)
    - aw3c2 14y ago
      you apparently never were on a stage, bring illuminated by giant lights. it often is uncomfortably hot. this is also a problem in video recording.
      - ars 14y ago
        And this would make it worse. It cools the lamp by sending the heat outward in the form of light. It does not cool the recipient in any way, in fact it requires that the recipient already be cooler than where the lamp is.
        aw3c2 14y ago
        oops, my bad. I thought I understood it from the comments here and did not read the article.
    - gsivil 14y ago
      I am sorry that I cannot elaborate more on that for now(4am) but the cooling effects of light are known for quite some time already. Please check laser cooling as a keyphrase.
  - ars 14y ago
    Keep in mind it only works if the light is being sent to an area that is cooler than where the lamp is. It's basically converting the heat difference into light. So you can't use it just to cool, it doesn't work that way.
    - davorak 14y ago
      I think where the light is being sent is open space so what ever temperature the local background radiation is at; a common local minimum being the cosmic background radiation.
      - ars 14y ago
        > a common local minimum being the cosmic background radiation No, that's only if you are in outer space. On earth it's the temperature of the air, or the walls. It doesn't matter if the light eventually gets to outer space - what matters is that there is something hotter near you (namely the air). i.e. it's not where the photons end up that matters, it's the total of all the photons that are being sent in your (the lamp's) direction that counts.
        davorak 14y ago
        Sorry if what I said was unclear. > it's not where the photons end up that matters, it's the total of all the photons that are being sent in your (the lamp's) direction that counts. This is what I was referencing when I siad "the local background radiation." The common minimum was supposed convey high frequency when choosing a random spot in the known universe. > On earth it's the temperature of the air, or the walls. The temperature of the air only comes into play if it is emiting radiation at the frequency of light produced by the led and at greater intensity. I do not see why this would be required.
        ars 14y ago
        > The temperature of the air only comes into play if it is emiting radiation at the frequency of light produced by the led and at greater intensity. Blackbody radiation. Air (everything) always emits light. > I do not see why this would be required. It's a fundamental law of thermodynamics that requires a heat source and a cold source in order to convert heat into some other form of energy. The air around you is the cold source, and the LED lamp is the hot source. If the LED is colder than the air it will not work - the LED must be hotter (in this particular case they put it in an oven).
nl 14y ago
This is one of the best things I've seen invented in a long time. It's like a peltier cooler[1], but it produces light instead of heat. I'm thinking of the most amazing beer cooler/Christmas light display ever! [1] http://en.wikipedia.org/wiki/Thermoelectric_cooling http://en.wikipedia.org/wiki/Thermoelectric_cooling
- ars 14y ago
  It does NOT cool things. To use it you have to heat it hotter than wherever it is shining into. It uses that heat to make light, but it is not a cooler (i.e. a heat pump).
  - davorak 14y ago
    The led itself should cool down if it is producing more power in light then is being put in electrically. The energy is coming from the the lattice phonons and as a result the lattice cools down. The paper[1] behind a pay wall show has a graph showing its cooling power vs current. I think where the light is shining into is open space so the source temperature has to exceed what ever temperature the local background radiation is at; a common local minimum being the cosmic background radiation. [1] http://prl.aps.org/abstract/PRL/v108/i9/e097403 http://prl.aps.org/abstract/PRL/v108/i9/e097403
    - ars 14y ago
      Yes, the LED is cooling down, but it will not cool down any lower than the ambient air. i.e. you can not use this as an A/C - you must already have a cold source in order to use it. The cosmic background radiation is not exactly common. You'd have to be in space. BTW, I don't think we are actually arguing.
      - electrograv 14y ago
        I don't understand. Why can't it cool down more than ambient air? You put in X amount of power, and you get out 2X amount of power as light -- therefore additional energy is being taken in as heat and converted to light. Say you direct that light AWAY from the area through mirrors or something so it doesn't heat anything nearby up. Then, by simple energy thermodynamics, you can show that X amount of energy IS being taken away from this local system and deposited elsewhere as light. Unless you claim that the LED stops producing the >100% efficiency levels at room temperature, I don't see why you're claiming it can't cool anything down.
dudus 14y ago
I'm pretty sure this is the first step to create an Arc Reactor. Tony Stark built it in a cave ... with a box of scraps
ars 14y ago
Previous discussion: http://news.ycombinator.com/item?id=3669688 http://news.ycombinator.com/item?id=3669688
quarterto 14y ago
In the UK, a microlight is an ultralight aircraft[1]. This would have been so much more badass. [1]: http://en.wikipedia.org/wiki/Microlight http://en.wikipedia.org/wiki/Microlight
sageikosa 14y ago
Energy input and heat in the "thermodynamic system", versus energy output and heat remaining stays in balance. If energy input (in electric current) is higher than energy output, then heat is added to the system. If energy input is lower than energy output, then heat is lost from the system. All it takes is the ability to channel some of the light (energy output) away from the reservoir of heat to show that the reservoir of heat will decrease. Ultimately you'd expect a temperature gradient at the system boundary to start transferring heat back into the system. through the first law of thermodynamics.
beej71 14y ago
It says it produces too little light for "most" applications... I wonder what the applications actually are!
- frugalfirbolg 14y ago
  Probably entanglement and other optics experiments if the light produced has the right properties.

48 points by jnand 14y ago

eck 14y ago

The title (and the first comment on the link) makes it sound like it's a perpetual motion machine, but as far as I can tell it's more like a tiny heat-pump: energy is conserved, entropy increases. Still kind of neat though.

Cushman 14y ago
Of course they didn't beat thermodynamics, but still, assuming they can scale the tech up to a useful power, it's a light that's also a cooling element. That'd be more than kind of neat, wouldn't it?
- Ygg2 14y ago
  But where would you use light that cools? Fridge lights? House lighting in warm regions? Hmmm. On second thought it could have interesting applications depending how much it cools.
  - nagash 14y ago
    Data centers.
  - mbreese 14y ago
    Lighting is hot. I'd love to have lights that weren't also little heaters. Or, if the cooling effect is big enough - imagine solid state cooling on devices. Who needs a fan when you can have a little cooling light? I doubt that they'll be able to scale this up too much though, since it probably relies on an effect that only occurs below a certain threshold.
    - swombat 14y ago
      Most LEDs don't heat up that much... they're usually cool to the touch. I'd love a computer that glows brighter to release heat when it gets too hot, though :-)
  - aw3c2 14y ago
    you apparently never were on a stage, bring illuminated by giant lights. it often is uncomfortably hot. this is also a problem in video recording.
    - ars 14y ago
      And this would make it worse. It cools the lamp by sending the heat outward in the form of light. It does not cool the recipient in any way, in fact it requires that the recipient already be cooler than where the lamp is.
      - aw3c2 14y ago
        oops, my bad. I thought I understood it from the comments here and did not read the article.
  - gsivil 14y ago
    I am sorry that I cannot elaborate more on that for now(4am) but the cooling effects of light are known for quite some time already. Please check laser cooling as a keyphrase.
- ars 14y ago
  Keep in mind it only works if the light is being sent to an area that is cooler than where the lamp is. It's basically converting the heat difference into light. So you can't use it just to cool, it doesn't work that way.
  - davorak 14y ago
    I think where the light is being sent is open space so what ever temperature the local background radiation is at; a common local minimum being the cosmic background radiation.
    - ars 14y ago
      > a common local minimum being the cosmic background radiation No, that's only if you are in outer space. On earth it's the temperature of the air, or the walls. It doesn't matter if the light eventually gets to outer space - what matters is that there is something hotter near you (namely the air). i.e. it's not where the photons end up that matters, it's the total of all the photons that are being sent in your (the lamp's) direction that counts.
      - davorak 14y ago
        Sorry if what I said was unclear. > it's not where the photons end up that matters, it's the total of all the photons that are being sent in your (the lamp's) direction that counts. This is what I was referencing when I siad "the local background radiation." The common minimum was supposed convey high frequency when choosing a random spot in the known universe. > On earth it's the temperature of the air, or the walls. The temperature of the air only comes into play if it is emiting radiation at the frequency of light produced by the led and at greater intensity. I do not see why this would be required.
        ars 14y ago
        > The temperature of the air only comes into play if it is emiting radiation at the frequency of light produced by the led and at greater intensity. Blackbody radiation. Air (everything) always emits light. > I do not see why this would be required. It's a fundamental law of thermodynamics that requires a heat source and a cold source in order to convert heat into some other form of energy. The air around you is the cold source, and the LED lamp is the hot source. If the LED is colder than the air it will not work - the LED must be hotter (in this particular case they put it in an oven).

nl 14y ago

This is one of the best things I've seen invented in a long time. It's like a peltier cooler[1], but it produces light instead of heat. I'm thinking of the most amazing beer cooler/Christmas light display ever! [1] http://en.wikipedia.org/wiki/Thermoelectric_cooling http://en.wikipedia.org/wiki/Thermoelectric_cooling

ars 14y ago
It does NOT cool things. To use it you have to heat it hotter than wherever it is shining into. It uses that heat to make light, but it is not a cooler (i.e. a heat pump).
- davorak 14y ago
  The led itself should cool down if it is producing more power in light then is being put in electrically. The energy is coming from the the lattice phonons and as a result the lattice cools down. The paper[1] behind a pay wall show has a graph showing its cooling power vs current. I think where the light is shining into is open space so the source temperature has to exceed what ever temperature the local background radiation is at; a common local minimum being the cosmic background radiation. [1] http://prl.aps.org/abstract/PRL/v108/i9/e097403 http://prl.aps.org/abstract/PRL/v108/i9/e097403
  - ars 14y ago
    Yes, the LED is cooling down, but it will not cool down any lower than the ambient air. i.e. you can not use this as an A/C - you must already have a cold source in order to use it. The cosmic background radiation is not exactly common. You'd have to be in space. BTW, I don't think we are actually arguing.
    - electrograv 14y ago
      I don't understand. Why can't it cool down more than ambient air? You put in X amount of power, and you get out 2X amount of power as light -- therefore additional energy is being taken in as heat and converted to light. Say you direct that light AWAY from the area through mirrors or something so it doesn't heat anything nearby up. Then, by simple energy thermodynamics, you can show that X amount of energy IS being taken away from this local system and deposited elsewhere as light. Unless you claim that the LED stops producing the >100% efficiency levels at room temperature, I don't see why you're claiming it can't cool anything down.

dudus 14y ago

I'm pretty sure this is the first step to create an Arc Reactor. Tony Stark built it in a cave ... with a box of scraps

ars 14y ago

Previous discussion: http://news.ycombinator.com/item?id=3669688 http://news.ycombinator.com/item?id=3669688

quarterto 14y ago

In the UK, a microlight is an ultralight aircraft[1]. This would have been so much more badass. [1]: http://en.wikipedia.org/wiki/Microlight http://en.wikipedia.org/wiki/Microlight

sageikosa 14y ago

Energy input and heat in the "thermodynamic system", versus energy output and heat remaining stays in balance. If energy input (in electric current) is higher than energy output, then heat is added to the system. If energy input is lower than energy output, then heat is lost from the system. All it takes is the ability to channel some of the light (energy output) away from the reservoir of heat to show that the reservoir of heat will decrease. Ultimately you'd expect a temperature gradient at the system boundary to start transferring heat back into the system. through the first law of thermodynamics.

beej71 14y ago

It says it produces too little light for "most" applications... I wonder what the applications actually are!

frugalfirbolg 14y ago
Probably entanglement and other optics experiments if the light produced has the right properties.