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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$\begingroup$ Who says that red light is used in light houses?? $\endgroup$– nasuCommented Oct 9, 2021 at 7:05
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$\begingroup$ Possible duplicates here and here. $\endgroup$– joseph hCommented Oct 9, 2021 at 7:42
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$\begingroup$ Can anyone answer it? physics.stackexchange.com/q/670687/313211 $\endgroup$– user313211Commented Oct 9, 2021 at 8:00
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$\begingroup$ @josephh FYI This user and the OP in your first link are one and the same. $\endgroup$– Bob DCommented Oct 9, 2021 at 14:28
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$\begingroup$ @BobD Thanks.-- $\endgroup$– joseph hCommented Oct 9, 2021 at 20:12
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1 Answer
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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
answered Oct 9, 2021 at 8:22
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$\begingroup$ +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. $\endgroup$ Commented Oct 9, 2021 at 8:57
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$\begingroup$ @ gandalf61 , true, good points $\endgroup$ Commented Oct 9, 2021 at 9:13