O.K… After watching the Hunt for Red October yesterday, a question that has gnawed at me for years came to a head.
In military command centers, subs, ships, they are almost always lit by either a low red, blue, and some times green light source. It looks cool, but there has to be a better reason than that. At first I thought it was for glare or something like that. But when I visited a civilian air traffic control center (Mpls/St. Paul International) it was dimly lit with white light. No funky lighting to be found.
Why the different color for background light in these institutions? Did someone say, ‘Hey, a lowly lit red room is better than low lit white room?’. If this were true, than why sometimes blue or green?
What I was told is that red light will not contract your pupils like white (and presumably other colored) light will. Thus if you needed to surface at night and look around, there would be no need to adjust your eyes to the low-light conditions.
traditionally a dim red light was considered best so as to not lose your night vision but I understand that other colors have been used more recently. I still use red and it works for me.
So why then would there be a worry about people in a command center losing their night sight? There’re not going to be running outside anytime fast.
I can see where this application would be usefull in a darkroom or car console situation, where the extremes are signifigant, but not a command center which is entirely enclosed and people are stationary.
well, I assume you do have some people who need to come in and go out. (I am assuming a light seal that allows no light to get outside) If a guy is not on duty and is somewhere where no one comes in, I guess he can use any light he wants. I have sailed on a tall ship and when I was off watch in my bunk I would use a white light to read and no one would complain (of course it was not strong enough to bother others). But if you really want to piss someone off, shine a flashlight into his face (he’ll be blinded for a while). I always have a flashlight or two with a red lens to use on the boat.
The parascope. Although surfacing to parascope depth to visually identify a target is not as common as it was in the U-boat days, it can still happen. The captain has to be able to go from looking at a map or sonar screen to looking for a grey ship against a black sky and black sea on a moonless night. Preserving the captain’s (or whoever else might be looking out of a parascope) night vision would be advantagous under these circumstances.
Having served in the Royal Navy I can answer this on a practical level.
Night vision takes a fair old while to acquire, over twenty minutes for the full effect, but is lost in a matter of seconds.
When someone uses a camera flash on you it takes some time for the bright spot to disappear, much more so if the room is already fairly dark.
When you go to bed and switch out the light it seems as black as the inside of the devils pocket but later when you get up to go to the bathroom you may well find that you can see enough to make it without ligthing up and waking th ewhole house, in fact if you did do so you find it is physically uncomfortable.
On board ship there are places that are always on low light, places like ops, electronic warfare and sonar, this allows the watchkeepers better contrast on the displays.They usually are not keen to leave their posts even to go for a leak during their shift as it takes too long to get low light vision back, which is why on larger ships there is often a toilet in an area where you don’t have to leave low light conditions.
If you turn up the display to counter ambient light the definition is poorer, the blobs on the screen tend to bloom.
On subs the place you usually see is the area near the periscope in the films and that is the ops room but many subs are so small that people are passing through to get somewhere else so it is easier for all concerned to darken the whole thing.
I have always seen red used but I have heard other colors have also been used. The main thing of course is that it be very dim so your eyes are at their most sensitivity. Red seems to be a good choice for several reasons. One is that dim incandescent lights contain mostly red to begin with.
Hmmm… I always thought part of the reason was that if some of the light DID leak out that it wouldn’t be visible at a long range to help point you out to the enemy. Red light doesn’t create a lot of light noise to bounce all around.
I am not sure about that. I would guess background (moon and star) light at sea would contain more blue and green than red. OTOH you have the eye being less sensitive to it… who knows
When I was in the navy (early eighties) the line was that faint red light would not destroy visual purple in the retina, wrecking night vision. Curiously I never found the mytical red lens goggles talked about in the Bluejacket Manual or worked in many places with red light. Under most night conditions there were a few faint yellow lights on the islans that gave infintesimal light to the flight deck.