6 or 12 Volt The vast majority of motorcycles since the 1970's have had 12 Volt systems. By the 1980's 6 volt system were unusual on all but smaller CC and off road motorcycles. Bulbs are usually marked with their voltage and wattage. Either scribed on the metal section or printed on the glass. 6 Volt batteries have 3 cells and 12 Volt batteries 6 cells.
Headlights On very early Motorcycles Headlight were powered by acetylene gas. Electric powered headlights were not commonly introduced until the late 1920's. First use in the 1960's the Halogen bulb came into common use in the 1980.
Incandescent light bulb This is the common type of filament bulb and creates light by incandescence. An electrical current passes through a thin filament, heating it and causing it to become excited, releasing thermally equilibrated photons in the process "Light". The enclosing glass bulb prevents the oxygen in air from reaching the hot filament, which otherwise would be destroyed rapidly by oxidation.
LED Bulbs are increasingly being adopted for signalling functions such as parking lamps, brake lamps and turn signals as well as Daytime Running Lamps, and in those applications offer significant advantages over filament bulbs. These include low energy consumption, long life, and resistance to vibration.