The car headlight bulb is underrated but highly important automotive parts which are often used as headlights, turn signals, and brake lamps. Without the auto bulbs, one is not allowed to drive after sunsets and the driver might have to pay a hefty price in return to the cop. Moreover, these are required to comply with national and international regulation decided by the concerned department. The other lighting applications like auxiliary lamps and interior lighting may not be regulated by the governing body.
The World Forum for Harmonization of Vehicle REgulations develops and maintains light sources acceptable in vehicle lamps. They have regulation 37 which has specifications of filament lamps and Regulation 99 which covers high-intensity discharge lamps. A few UN approved headlight bulbs for car are also permitted along with other regulations.
As per the Regulation 37, filament lamps are classified into three categories - those without general restriction, those acceptable for signaling and the ones which are no longer allowed as light sources for new types but are permitted for production as a replacement part.