Interesting thread, here is my contribution for what its worth.
I am a recent convert to night spearfishing, having spearfished in the daytime for 25+ years. Like everything to do with the sea I agree with the KIS, but I always use a float when night diving, not for the visibility angle, but for safety, as a buoyancy aid.
I’m paranoid about getting snagged in nets at night or getting caught in the tide. My thought is that my float (which is attached to me with a piece of floating rope rather than cord) doubles up as a flotation device which if I needed to I could pull myself up to and then use to support me while I cut myself clear. I carry a spare torch, spare knife and ‘tough cut’ scissors as well as the usual goody bag and fish stringer on my float.
Only negative is the hassle of getting snagged up in the float line, but I find using floating rope reduces this and the drag effect of rope over cord is minimal.
My float is a catamaran design made of 2 boat fenders side by side with a goody bag strung across the middle which is a safe place to store gloves, mask etc when walking up and down the beach.
Torches?
I use a UK D8R which seems to me as bright as you can reasonably get, being rechargeable has low running costs. I had a problem with bulbs popping when I first bought the torch, but Kent Diving were excellent and sent me replacements parts without question. The torch has 2 bulbs (1 x 14 watts 370 lumens and the other 30 watts which is fish fryingly bright) Burn time is about 1.5 hours, although this is quoted at 7 hours if used on the lower power setting. The fact that if one bulb blows mid dive you can switch to the other without any interruption to your dive was a good safety factor for me when choosing it.
I also use a UK mini Q40led which I attach to my mask strap with a piece of bicycle inner tube this is useful as a back up and as a handsfree headtorch arrangement for stringing fish etc
I have to say that I’m not a big fan of LED’s they somehow just don’t seem to have the ‘guts’ of a conventional light. I am slowly replacing the conventional spotlights in my home, I find that the LED spotlights, even though being rated the same just are not somehow as bright?
As a diving experience there is nothing like a calm starry moonless night with the sea alive with nocturnal creatures and I would recommend everyone to give it a go. Certainly the imagination works overtime and there is nothing like a solo night dive to sharpen your senses.