Night diving has some things in common with cave diving -- you are very depending on your dive lights, to know where you are, to see stuff, and to communicate.
In cave diving, you spend quite a bit of time on what's called light discipline. What is it? It is learning how to use a light in the dark so that it helps you AND your team, and doesn't become a problem.
First off, you use your light in smooth, fluid movements. If you are swimming along and looking at stuff, you swing your light back and forth in a fairly slow and rhythmic fashion. If you are really disciplined, you make sure your light crosses in front of your buddy's field of view every 30 seconds or so, so your buddy can use that information to conclude that you are well. Rapid, jagged, or erratic light movements will alert a trained buddy to the fact that you are having some kind of problem, and a well-trained buddy will ask you if you are okay, or even stop and turn around to see if you're all right.
Second, if you are using hand signals, you light your hands, and in such a way that the light crosses in front of your body, rather than shooting out toward your buddy. If you don't light your hands, your buddy likely can't see your signals. If your light gets too close to in front of you, your buddy will see stars but nothing else!
And that leads to the next concept, which is never to shine your light in your buddy's eyes. Human eyes are capable of an enormous amount of accommodation, to account for low light. It takes very little illumination to be able to see in the dark, which is why I personally do my tropical night dives on a backup light. But if you shine your light in someone's eyes, it will be 30 seconds or more before they can see anything to speak of at all, which means that, to all intents and purposes, they are blind. Any time you look at your buddy, keep that light aimed down -- you can move it up if you need to "paint" them to check something.
I think all of the above are generally agreed upon, but I'll add a last little bit which is my own. As mentioned above, the human eye is capable of enormous light-gathering if allowed to do so. This means that, if you are night diving in clear water, you really need very little light with you. Nocturnal animals don't LIKE light, and if you are waving a big video light around, many of those critters will have hidden before you ever get near them. A good backup type light (UK SL4 eLED or DRIS backup, for example) is plenty, in my personal opinion. The murkier the water, the more power you need, but in the tropics, small lights work just fine.
In cave diving, you spend quite a bit of time on what's called light discipline. What is it? It is learning how to use a light in the dark so that it helps you AND your team, and doesn't become a problem.
First off, you use your light in smooth, fluid movements. If you are swimming along and looking at stuff, you swing your light back and forth in a fairly slow and rhythmic fashion. If you are really disciplined, you make sure your light crosses in front of your buddy's field of view every 30 seconds or so, so your buddy can use that information to conclude that you are well. Rapid, jagged, or erratic light movements will alert a trained buddy to the fact that you are having some kind of problem, and a well-trained buddy will ask you if you are okay, or even stop and turn around to see if you're all right.
Second, if you are using hand signals, you light your hands, and in such a way that the light crosses in front of your body, rather than shooting out toward your buddy. If you don't light your hands, your buddy likely can't see your signals. If your light gets too close to in front of you, your buddy will see stars but nothing else!
And that leads to the next concept, which is never to shine your light in your buddy's eyes. Human eyes are capable of an enormous amount of accommodation, to account for low light. It takes very little illumination to be able to see in the dark, which is why I personally do my tropical night dives on a backup light. But if you shine your light in someone's eyes, it will be 30 seconds or more before they can see anything to speak of at all, which means that, to all intents and purposes, they are blind. Any time you look at your buddy, keep that light aimed down -- you can move it up if you need to "paint" them to check something.
I think all of the above are generally agreed upon, but I'll add a last little bit which is my own. As mentioned above, the human eye is capable of enormous light-gathering if allowed to do so. This means that, if you are night diving in clear water, you really need very little light with you. Nocturnal animals don't LIKE light, and if you are waving a big video light around, many of those critters will have hidden before you ever get near them. A good backup type light (UK SL4 eLED or DRIS backup, for example) is plenty, in my personal opinion. The murkier the water, the more power you need, but in the tropics, small lights work just fine.