The most common night dive is just a dive, at or after sunset, to see a different side of marine life and a lot of animals that are more active, or only come out, at night. Mandarinfish dives--you go down and kneel in coral rubble just before sunset. And wait. Maybe you see mandarinfish which are gorgeous and very shy, maybe not; maybe you see them mate, maybe not. Once or twice a trip works for us (ideally, mandarinfish dives morph into regular night dives when the fairly-brief show is over). Blackwater dives--you drift along under a boat in pitch black water except for big lights strung below the boat, almost always at 5, 10, and 15m, which attract little things which you try to photograph. Very much an acquired taste--you can go the whole dive without seeing anything except once in awhile that the lights are kinda far off, or you can see and attempt to take pictures of all kinds of things. It's about at close as it gets to a spacewalk.