Red or blue lights?

Refering to the question: Why are red lights used in darkened control rooms and other low-light situations?
In the mid '80s I was in the army serving as a tanker. We removed all the red filter lenses from the tank internal lights and replaced them with blue filters. Was this to reduce visability from enemy night vision devices or because blue was found to be better in preserving our night vision?

Neither; as the article points out, both of these are uses of red light. If you switched to blue lights, it was to see better.

“Neither…it was to see better”? Why not switch to white light then? I guess that I was looking for a reason to go to the trouble of the Army buying new lenses, shipping them all over the world (Germany in this case), and changing out apparently servicable red lenses for these blue ones.

I have a bitch of a cold and am running on little sleep, but what I’m gathering from a little Googling is blue lights stimulate your rods, which are used for night vision, and which are not very responsive to red. Red lights are better if you’re transitioning from red to white light as your eyes will adjust better. But if you’re in a tank out in the Iraqi desert at 1am, I suspect this isn’t an issue which is why they switched.

At least, that what I’ve been lead to believe. You can read more here and here, for starters.

Thanks for the answer Patch. Your research inspired me. I found the following that seemed to explain it fairly well.

“By the mid-60’s, scientists had discovered that red-light saturation actually decreased night-vision, to some extent. It wasn’t necessarily the hue of the light that affects night-vision (though that fact is still debated), but rather the intensity of illumination. See, red-hued light requires almost twice as much illumination to provide the same candle-power as lower-frequency (420-460 nm) blue-hued light. Thus, red-light is prone to induce more glare, and will negatively affect the cones (photo-receptors) of the eye. Blue-green light at a lower illumination is actually better, providing more color “information” per degree of illumination.”

Interesting that it took 20 years for the Army to change our lights. Well, now I know. Thanks

I think dim blue light might provide for better peripheral vision than dim red, whereas the red would probably provide better central, detail vision. This is because the peripheral regions of the retina contains mostly rods (which are more sensitive to bluer wavelengths) plus a few blue sensitive cones, all spaced relatively widely apart. By contrast, the fovea, the central portion of the retina has densely packed red and green sensitive cones, relatively few blue sensitive cones, and no rods at all. Vision for fine detail (and for color) depends on the fovea and the nearby central regions because only here are the receptors packed closely enough together.

Perhaps, for some reason, good peripheral vision was considered to be more important in extanker59’s situation than good detail vision.

Could red light be the the way it was always done, and we are now finding that blue works better? Also, remember photographic dark rooms? At some stages, you could use a dim red light.

With some emulsions, you can use a red light all the way through. Orthochromatic B&W film was blind to red light. Panchromatic film, which replaced it in most cases, was not, so it had to be developed in total darkness, but generally produced images that looked more “right”, because red things didn’t come out black. Color film, of course, always has to be worked with in the dark.

I haven’t been in a darkroom for decades, but, the last time I was, B&W print paper could be used in red light. Since it only had to copy the B&W negative, being insensitive to red light didn’t matter.

But the technical problems of preventing night blindness are not the same.

And the reason why you can use red light in a darkroom is that the emulsion on photographic paper is orthochromatic, not panchromatic.

Here is a good example of how it comes out when you take a photo of a coloured object with an orthocromatic, instead of panchromatic, film (or perhaps glass plate in this case). The colours of the Swedish flag look reversed.

Do we have to go to red alert?

I will have to change the bulb.