I paddle at night a lot often as in the short days of winter, it's another way to get on the water rather than not at all. Sometimes in late summer, night paddles are great to see the bioluminescence (glow in the dark algae, etc). In either case, while night paddling, you have to use your senses more and keep an eye out for boats as not all use lights. Sometimes I'll stop and listen for motors, then proceed ahead. Living in Seattle, I deal with urban waterway paddling daily, so my senses are always on high alert.
In the US, human powered crafts (us) are required to show a white light in case of an encounter with another boat. This can be a waterproof LED or halogen flashlight or headlamp or one of the many waterproof lights available to attach to your PFD or board. I attach a Guardian LED waterproof light to the rear shoulder of my PFD to alert those behind or the side of me without ruining what little night vision I have. I have a wp flashlight on a string in my PFD front pocket, in case I need to show it at an on coming boat. One method to really show yourself off, just in case, is to angle a flashlight onto your board which should light the whole board up. There's a few great lights that can be attached to your board via a suction cup that offer nearly 360 degree coverage. I'd recommend attaching a safety line to a leash cup in case the suction fails.
Use a waterproof laser pointer for immediate emergencies where a boat is coming straight at you and there's no time to move. The best method is to aim the laser at the pilothouse of the boat, which has considerable effects in grabbing their attention. Only use the laser for this purpose, as the light is damaging to your or other folk's eyes. Attach a string to the pointer for storage in your PFD to prevent it from dropping in the water.
I also attach reflective silver tape on my paddle blades on both sides which reflect a boat's lights quite well. On sunny days, the sun will also reflect off your paddle and assist with boaters in seeing you. You can stick strips of the tape on your board if desired.
Check out Northwest Outdoor Center in Seattle for these products.