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This is a tangent, but it's crazy that we've built a communications network that relies on basically LEDs shining out of our pockets (with less interference from the sun, but still).



Except our pockets (unless you wear tinfoil pants) and many other materials are transparent at those wavelengths which makes it a lot less crazy.


You don't think making an antenna that can detect an LED shining in a flat miles away is crazy because pockets are transparent?


In darkness our eyes can easily detect a 1W LED from kilometers away.


But can they distinguish a specific 300 mW LED in a stadium with tens of thousands of other LEDs next to it?


If it were a different color, yes. If each of them were a different color, your eye would still be able to, as long as you had enough focus. So the analogy holds pretty well.


My understanding is that healthy human eyes are able to detect individual photons.


No. Amateur radio operators have done it, and it’s not difficult to imagine how one would.


That doesn't make it any less amazing.


Indeed, nothing is difficult to imagine how to do if the method is common knowledge.




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