So I was pulling a dead taillight bulb out of my car today, and noticed that the two bulbs in each taillight are actually not interchangeable (I have a 2001 sedan). The outer bulb (closest to the side of the car) is a single-filament bulb, whereas the inner bulb has two filaments (and offset prongs). Given that it's the outer bulb that lights up brighter when you brake, why do they use a dual-filament bulb for the inner light? What kinds of advantages does a dual-filament bulb have over single-filament? Longer life? More light with less current?