Why red lighting on a submarine?

Why do they use red lights on a submarine when in combat?

I've read a few webpages on the subject but can't find anything conclusive.

I guess there are two parts to the question: why not use white light, and if you use a colour, why red?  I read that the eye is more receptive to green so 'less' green would be needed and objects would be less 'coloured', and that reading in red light will make eyes more tired.  The advantage for red light seems to be that eyes can adjust to darkness more quickly but I don't see how that's good - if a sub goes dark surely you're screwed anyway?!
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On British submarines there is an area set-aside as the "bunk space", which contains all the beds or bunks for the crew. Each bunk is approx. 2 metres long by 1 metre wide by 1 metre high, and is often shared by two men who are in different shifts or "watches". The principle is; as each man gets up to go "on watch" he rolls up his own sleeping bag, and rolls out the sleeping bag of the man coming "off watch". During the normal operations of a submarine the sleeping area will only be lit by dim red lights, so as to enable the off watch sailors to sleep. The only man who has his own room, or cabin, is the Commanding Officer


Submarines employed a "RED" lighting system in the control room and conning tower to allow for better night vision. Often, crew members on watch would wear red colored goggles when moving through areas of the boat not covered by red lighting. The red lights (or goggles) would allow their eyes to adjust to the night's darkness quicker when on watch, thus giving them a considerable advantage. It's use is limited obviously in Silent Hunter . . . but it adds a nice touch of authenticity. It might reduce the possibility of your periscope being spotted by the enemy at night if you were using only white lights.

Would people be looking out the periscope?
What else would they be doing with it?
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If they are looking out of it, they may have to adapt their vision from interior lighting to exterior lighting.
If they are too deep to use it, or are trying to reduce turbulence or sonar signature, then interior lighting might be decided by other considerations.
I do not know anything about submarines, but just want to draw your attention to the fact that red light is actually on the low edge of the energy spectrum. This has several implications, amongst them :

- The fact that red light does have less possibility to start chemical reactions (eg. clothing will keep more its colors if used only in red light than in broad daylight).
- You could lower the tension of the light bulbs, which gives a lower energy requirement and a longer lifetime of the bulbs.

Also take in mind that the red LED's were the first one's in use on a massive scale.

To think about and eventually to be completed by some collegues...

Normally, subs did use to have a watch on the bridge at all times. At night, using red light inside makes for quicker dark adaption of the eyes when you step outside.
Probably, a falure in the light circuits, due to some kind of hostile action like depth charges in the vicinity, would cause darkness and, perhaps, reserve lights coming on. Having eyes partly adjusted to darkness would minimise the "blind" time for the crew in the control room.
Even today, with sonar and radar, many subs don't use them for collision avoidance, as emitting any noise or radio waves reveals their position.

So whenever the sub is on the surface, there have to be two to four crewmen on top, each scanning a sector with binoculars.
A sub may need to surface at any time, so there always have to be several crewmembers night-adapted.  That's what the red lights are for.

Periscopes work both ways.  If you can see out from a periscope, then what's on the surface that you are looking at can also see the lighting inside the room where the periscope is housed.  If the periscope is in a brightly lit room then the observed object would see a pinpoint of light in the middle of the sea.

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Extending infex's comment:

Another reason might be to do with spark safety.  A sub will contain highly flammable/explosive material in a confined area.  Historically there would not be the same technology as is available today to eliminate the possibility of a spark causing an explosion on board.  So lighting had to be as low energy as was possible to minimise risk.
>surely you're screwed anyway?!
...applies also to other environments that use red lights  ;-)
here's by guess - the men can still do their jobs in red light, but the bulbs use less power - electrical power was critical on a WWII U boat.
another thought would be "it would be more freaky if they used lavender lighting in a sub"

but the red light is the lowest frequency on the spectrum that is discernable by the human eye.  I guess in low light (or should I say red light) situations, every other light source other than red should jump out at you.

danieloneillAuthor Commented:
Cheers folks, it's been interesting reading for the last couple of days!  I don't know that we got a final answer but they all made sense and are probably contributing factors to the decision to use red lighting.  I split the points evenly between everyone so I hope that's OK - all the answers sound right!

Maybe if anyone finds any authoritative answer they might post back here in the future: I'm glad that it's not just me who's wondering now :)
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