bulbs create a bigger drain on the battery, which means the voltage regulator diverts more current to the battery, which means less is available for the engine (especially the engine management system). up to a certain point this makes no difference because the amount of current available for the engine is greater than or equal to the engine's requirements. once you go past that point the engine suffers and you lose mpg, and just as important you lose power. the most extreme example of this is when you stick a fully charged battery on a car with a fairly dodgy alternator (such as one with worn brushes). the engine immediately lacks power and within a very short time you struggle to get high revs (since high revs means greater current requirement). eventually it gets so bad that you cut out.
theory aside, the actually difference from using your headlights isnt going to be noticable, but its my excuse for not using them and i'm sticking to it.
theory aside, the actually difference from using your headlights isnt going to be noticable, but its my excuse for not using them and i'm sticking to it.