A website touting the Sylvania SilverStar headlight bulb says it provides "up to 30 ... in our labs and at our test track. We tested the low-beam performance of single-filament (9003) and dual ...

i.e. the area of the lens directly over the low-beam bulb. Mark this spot on the headlight by making a small dot with a dry-erase marker. Make a corresponding mark on the other headlight.