power consumed at bulb is my only concern. Automotive bulbs are rated at 12.8v.


I know filament lights are not a plain resistive load, but it was close enough for the non instrumented load guessing here.

if I use this equation



then it would be 68 watts at 11.5v etc.

Or
12.8v 6.25A
11.5v 5.92A


I found this listing on a site selling voltage regulators for halogen bulbs, do the math.