Question: what is the difference between h1 and h4 bulbs?
Answer: The primary difference between the H1 and H4 bulbs is the number of filaments in each bulb. The H1 bulb is a halogen bulb, which contains a single filament that uses 55 watts at 12 volts. The H4 bulb is a dual-filament halogen bulb that uses 60 or 55 watts at 12 volts, depending on which filament is in use.