Battery pack configuration options.

Hi again... this is my second post now. I imagine I'll be doing a lot of asking before I have the knowledge to start answering.

I have decided on the size and type of my battery pack for my canister style dive light - I will be using 30 AA NiMH batteries (2700mAh) at 1.2V each.

The question is how do I configure it? I was planning to use roughly a 50W bulb so do I either:

1. Use a 50W 6V bulb and run with the pack configured so that it provides 7.2V and has a capacity of about 10Ah.

2. Use a 50W 12V bulb and run with the pack configured so it provides 14.4V and has a capacity of about 5Ah.

At first glance to a newbie like me the 6V option would be best as it has the greatest battery capacity... however there must be a reason most people use a 12V bulb instead...

Thanks for your input guys

In simple terms, to achieve 50W, the 6V bulb will have to be run at >8A, while the 12V bulb would do the same using half the current. The 6V pack will therefore be used up in the same amount of time. 4A is easier to handle than 8A, so I would go with the higher voltage.