How 'light house' actually work ?
How does light from light house appear to a ship far away and close away ? As colour can change due to scattering distance so does all ships either far or close see only one colour from light house I.e white?
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Who says that red light is used in light houses?? – nasu Oct 09 '21 at 07:05
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Possible duplicates here and here. – joseph h Oct 09 '21 at 07:42
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Can anyone answer it? https://physics.stackexchange.com/q/670687/313211 – Oct 09 '21 at 08:00
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@josephh FYI This user and the OP in your first link are one and the same. – Bob D Oct 09 '21 at 14:28
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@BobD Thanks.-- – joseph h Oct 09 '21 at 20:12
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Light houses worked by warning sailors of rocks/land by having a visible light there.
Air scatters light mainly in the blue part of the spectrum, so from far away the light might appear redder than the original source - although it didn't really matter to the sailors what frequency of light was visible.
Early lighthouses used a fire for the light source, presumably with a red/orange light - for example Egypt's Pharos of Alexandria, built around 280 BC.
Later lighthouses had a light source that rotated and focused the light into a narrow beam, so that it could be seen from further away.
You might want to look into Fresnel lens
John Hunter
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+1 for excellent answer. Also worth noting that the rotating lens means (a) ships see a flashing light which makes the light more noticeable and (b) ships can use the frequency and pattern of flashes to identify individual lighthouses. – gandalf61 Oct 09 '21 at 08:57
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