The headlight bulb is the source of low and high beam light: two filaments of different brightness are switched from the handlebar. Low beam + high beam bulb.
Replace it if one of the filaments has burned out or the light has become dim. Before buying, check the base type, the 12 V voltage and the wattage against the previous bulb. Do not touch the bulb with your fingers. When replacing, also inspect the neighboring parts of the assembly: they wear out together.
