Linked Questions
11 questions linked to/from Why does conservation of étendue matter when showing one cannot focus light to arbitrary temperatures?
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XKCD Focusing moonlight - Only the component of light perpendicular to a surface heats the surface? [duplicate]
Is this XKCD https://what-if.xkcd.com/145/ saying that a surface is only heated by the component of the rays that are perpendicular to the surface?
Conservation of étendue:
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Why don't objects get brighter when I reflect their light back at them?
In a well-lit room, a light source shines light on the objects in the room, some of which reflects back off the objects. We can make the light source brighter by causing it to emit more photons, which ...
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How is the Earth heated by a Full Moon?
While the moon is certainly not a good reflector of solar radiation, surely the radiation it reflects back heats the Earth (even if it is a terribly small amount).
How would one go about calculating (...
user28754
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Does putting an aperture in a laser beam make the smallest point it can be focused to larger or smaller?
If you put an aperture in a laser beam to block some of it, I would imagine that the spot it can be focused to becomes larger due to diffraction. The numerical aperture of the system is limited by ...
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Conservation of energy when focusing black body radiation on another black body
This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics and/...
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Is it possible to use a lens to focus sunlight to a point hot enough to fuse hydrogen? [duplicate]
Is it possible to use a lens to focus sunlight to a point hot enough to cause atomic fusion?
The point of the diagram below is to create a focused point of light at a point in space that is far from ...
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What specific properties of laser light make it dangerous?
What makes a laser more dangerous than a high powered single color LED for example?
Is it the fact that it's coherent light, all the photons have the same wavelength, that it can be focused to a small ...
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Laser beam focus
Why isn't it possible to focus a laser beam to an infinitely small point in space? I am familiar with the shape of a gaussian beam, but why can't my $w_0$ be equal to zero?
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Is refraction of light a thermodynamic process?
Is refraction of light a thermodynamic process?
Can it be explained by conservation of energy?
If so, does temperature has an effect on refraction of light?
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Angular magnification (definition)
According to my physics book, "Angular magnification measures the change in the beam angle that converges in the image with respect to that of the beam emitted by the object and collected by the ...
user248666
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Does conservation of Etendue mean focusing+filtering a larger led bulb into a point light in a way that casts shadows like a point light is impossible
I unfortunately never took a class on photonics but this law of Etendue seems to be very relevant to a project I am not even sure is possible. I am trying to create a lamp that does something like ...
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