Quote Originally Posted by kc7jty View Post
A reader asks:
Will a 12 volt automotive incandescent dash light bulb give off as much light if it's powered with 12 v ac (60 hz) as opposed to 12 v dc?
...and if there's a difference, how much?
The bulb will dissipate the same amount of power in both cases, so if light output were solely dependent on that, the brightness would be the same.

However, the brightness, i.e. amount of visible light emitted is a highly nonlinear function of filament temperature, which in turn depends on filament current in a nonlinear fashion.

It's not inconceivable that the increased light output at ac peaks could offset the reduced light output at zero crossings. In any case, I'd expect the difference to be small.