Which is more efficient and why 5- 50w 120v halogen lights or 5- 50w 12v halogen lights run on a transformer?

Answer 1

In both cases, you're operating five 50-watt lights, so you're getting the benefit of

250 watts of power. You haven't said how much power you have to feed to them,

or which halogen light is more efficient, so we can't calculate any efficiency.

Just on general principles, the only difference in the two setups that we're sure of

is the transformer, and there's always a bit of loss in a transformer, so there's a

reason to speculate that the second situation is a bit less efficient. But aside from

that, we're woefully short of electrical information on which to base an answer.

By the way ... There's also no reason to expect that lights running on higher or

lower voltage are any more or less efficient than those designed for the opposite

conditions.