Charlie99:A bright HID light will overpower other lights, making light communications more difficult if your buddy has a less powerful light. Ideally, buddies should have similar lights.
Clearly, the more powerful the light, the better you can light things up. The HID also excels as a surface signalling device.
At some point, though, bright lights are counterproductive if what you came to do is to observe nocturnal marine life activity. Bright lights can turn night into day, but that kind of defeats the purpose of a night dive.
To observe marine life, I prefer to either turn off all lights, or use just just a tiny 0.4 watt 2 AAA light during much of the dive. It is amazing how much you can see using moonlight or the lights of other divers once your eyes have night adapted.
Although I don't have an HID light, I have had buddies with them, and have been in groups with them. On a clear water tropical night dive, I'd bring it along, but leave it off for most of the dive. OTOH, HIDs are absolutely fantastic at lighting up nooks, crannies and under ledges during the daytime when other lights are overpowered by the sun.
BTW, the one and only advantage of a 50W halogen cannister light is that you can turn it on and off at will.
I will often, on the rare big moon clear water night dive in SoCal, just turn the thing off for awhile. We did this weekend. Fantastic. After a few minutes, turn it back on.
You're right about buddy with a UK C4 and you with a 21w HID. Hence the "buddy light" - several of us have eBayed our playstations, eaten Top Ramin for a few months and saved our pennies to get a second HID as a "buddy light".
Kinda hard to have effective light communication when your buddy doesn't have a real effective light. Its one of the wiser investments I've made, to be sure.
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Ken
