Tacogirl, if i tell you a secret ,promise not to tell.
It seems like everything (all life) has just two rationale.
Survive and Reproduce and really i think survive is just to serve the latter... so when i'm trying to understand something like Bioluminescence i'm thinking they are trying to find one another with the glowing so they can have sex.
I've read that they meet near the surface at a time shortly after dark. Jellies reproduce usually all at the same time and when the water is warmer.
I dont think the moon is a factor for the jellies like it is the corals.
My guess is any warm calm night, just after dusk.
my observation is movement makes them fire their lights, something like stirring the water or the boats prop-wash.
The 'What The Hell Is It' book says it not a true jelly fish but a class called Ctenophora or 'Comb jellies'.