Going on a night dive? I live it too. But remember to bring not only a torch (and a back-up torch) but also a strobe light.
What is that?
It is creates a short burst of light. The light is brighter and more powerful and the burst shorter than the kind found when using traditional flash.
It is light (few grammes only), small (about 12 cm high), simple to use (on-off that's it). Wrap it around your arm as necessary and it will signal your position to a boat.
Not all divers have one, but I do keep it in my standard kit. Your never know what happens on a dive. You can get separated from your group, surface alone, etc.
Your torch will help to signal your position but well, why not having a precautionary measure ?
I am using this one for few years and it does the job.
Speak soon, back to diving.
The Diving Bear