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Comments on Why can someone observe light, even when the light fails to illume that someone?

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Why can someone observe light, even when the light fails to illume that someone?

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I never grokked the optics behind LightHouses and the WW2 poster below work. LightHouse beams are narrow and focussed.

Doubtless, the light source can fail to illumine a seafarer or the enemy submarine. But then how can the seafarer or enemy sailors behold your light source?

It counters intuition that although a light fails to illumine someone, that observer can still behold the light source! Can you please correct my intuition?

I never studied science after secondary school. Please explain like I am (1)5.

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The problem is not your intuition, but your assumptions. (1 comment)
The problem is not your intuition, but your assumptions.
celtschk‭ wrote almost 2 years ago

If the lighthouse bean fails to regularly illuminate a ship that's still in safe waters, it is either badly built or out of order. The ship's lights don't need to illuminate the submarine; it only has to reach the periscope. If the submarine doesn't have the periscope sticking out of the water, the people on it won't see the ship (but may still hear it).

If you can see something, light from it reaches your eye (or the camera, if photographed or filmed). Always.