Sorry, got busy with other things...
Lights are necessary at depth (which, depends on surface luminosity and water clarity), but then are only good for close shots (few feet). My limited experience with tropical water is that if you are going to be mostly diving shallow and do mostly wide shots, you will find little use for such lights.
However, if you find a nice critter at short range, lights will make it shine, literally (unless you are shallow and use a filter and do a successful manual white balance).
My advice, take your light.
