In my experience, and from what I've read, red light is kind of a special-purpose light for protecting dark-adapted vision that is not real useful for much else.
You have some cells in your eyes that are not sensitive to red at all. If you only let red light into your eyes, those cells become dark adapted. The cells that see red light lose their dark adaption, but they readapt relatively quickly.
By dark-adapted I am talking about retinal changes that take nearly a half hour, not just dilated pupils. I get the impression that when a lot of people talk about dark-adapted vision, they think they are referring to retinal changes, but really they are talking about pupil changes.
Dim light of any color will preserve dilated pupils. Only red light preserves dark-adapted retinas.
The reason I say red is not real useful for much else is that your eyes are about a bejillion times more sensitive to blue-green than to red. You can have a red light that is maybe even a little bright for reading, but when you try to walk around with it, the light seems to just evaporate. A yellow light, for example, that is maybe a little dim for reading can be used just fine for walking around when it is really dark outside.
If you use a dim yellow light when your eyes are dark-adapted, you will preserve most of your night vision, but not as much as if you use red. Probably most people will not see any difference unless they are doing something really vision-intensive, like star gazing. You'll definately notice the difference between dim yellow or amber and red then.
Another consequence of the eye's inability to see dim red light is that you can use it to avoid being seen by others. You can use about 100x more red light than cyan before you will be seen by an observer. Of course the military situation is a little different, because of the different sensitivities of night vision devices.
So if you are doing astronomy or similar, use red. If you are walking around, use yellow, or maybe even a dim cyan. A lot of sources indicate that yellow light is most easily focused, so produces less eye strain when reading.
I like:
- red for astronomy
- yellow for reading
- cyan for seeing things in the distance with binoculars
Colored lights are just more fun anyway.
Scott