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Grimaldi
Grimaldi
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I find xkcd‘s take on this very telling, it starts by asking a different question: How hot can you make something using optics?

The answer is: You can‘t make something hotter using optics than the temperature of the surface of the source. This means that you can‘t use optics to make fire with moonlight.

But why? The thermodynamic argument is that optics work „for free“ (they don‘t need energy). If you it was hotter, you would somehow gain energy.

The crux is, that the image in optics is not a point, but has some extent:

Basically optics is reversible, so you can‘t use optics to concentrate light from two different points A and B (on the sun) onto a single point E on earth, because if light goes back through the optical element, it must come from either A or B, but cannot go back to both.

Same applies to „bundling“ light, see XKCD.

But what optics can do, is to make you almost as hot as the surface of the source. And that means, as hot as the surface of the sun. And that temperature is - well - not good for your eyes (Proteins start to denaturate at about 60°C).

I find xkcd‘s take on this very telling, it starts by asking a different question: How hot can you make something using optics?

The answer is: You can‘t make something hotter using optics than the temperature of the surface of the source. This means that you can‘t use optics to make fire with moonlight.

But why? The thermodynamic argument is that optics work „for free“ (they don‘t need energy). If you it was hotter, you would somehow gain energy.

The crux is, that the image in optics is not a point, but has some extent:

Basically optics is reversible, so you can‘t use optics to concentrate light from two different points A and B (on the sun) onto a single point E on earth, because if light goes back through the optical element, it must come from either A or B, but cannot go back to both.

Same applies to „bundling“ light, see XKCD.

But what optics can do, is to make you almost as hot as the surface of the source. And that means, as hot as the surface of the sun. And that temperature is - well - not good for your eyes (Proteins start to denaturate at about 60°C).

I find xkcd‘s take on this very telling, it starts by asking a different question: How hot can you make something using optics?

The answer is: You can‘t make something hotter using optics than the temperature of the surface of the source. This means that you can‘t use optics to make fire with moonlight.

But why? The thermodynamic argument is that optics work „for free“ (they don‘t need energy). If it was hotter, you would somehow gain energy.

The crux is, that the image in optics is not a point, but has some extent:

Basically optics is reversible, so you can‘t use optics to concentrate light from two different points A and B (on the sun) onto a single point E on earth, because if light goes back through the optical element, it must come from either A or B, but cannot go back to both.

Same applies to „bundling“ light, see XKCD.

But what optics can do, is to make you almost as hot as the surface of the source. And that means, as hot as the surface of the sun. And that temperature is - well - not good for your eyes (Proteins start to denaturate at about 60°C).

Source Link
Grimaldi
Grimaldi
  • 473
  • 2
  • 6

I find xkcd‘s take on this very telling, it starts by asking a different question: How hot can you make something using optics?

The answer is: You can‘t make something hotter using optics than the temperature of the surface of the source. This means that you can‘t use optics to make fire with moonlight.

But why? The thermodynamic argument is that optics work „for free“ (they don‘t need energy). If you it was hotter, you would somehow gain energy.

The crux is, that the image in optics is not a point, but has some extent:

Basically optics is reversible, so you can‘t use optics to concentrate light from two different points A and B (on the sun) onto a single point E on earth, because if light goes back through the optical element, it must come from either A or B, but cannot go back to both.

Same applies to „bundling“ light, see XKCD.

But what optics can do, is to make you almost as hot as the surface of the source. And that means, as hot as the surface of the sun. And that temperature is - well - not good for your eyes (Proteins start to denaturate at about 60°C).