746 watts = 1 horsepower. The fog lights draw 55 watts each, 110 watts for the pair, or 0.15 horsepower. Since alternators are about 50% efficient (50%-62% dependent on speed, but I'm using the lower number due to other losses within the electrical system between the alternator and the fog lights), running the fog lights consumes around 1/4hp to 1/3hp. Even if it's the worse of the two numbers, that's still only about 0.4% of the engine's output. But it will result in worse fuel economy. Whether it's measureable is doubtful, but it will have some impact.I may not be able to measure it, but creating energy to light the lights uses some power.