Headlight bulbs come in different light sources, and there are different models within each source. H1 and H4 bulbs are common types of halogen bulbs that differ mainly in their construction, use and price.
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.
H4 bulbs function as both high-beam and low-beam headlights with a single reflector. They are the most common bulb used in motorcycles. H1 bulbs, on the other hand, require two bulbs for each headlight, each with its own reflector.
H1 and H4 bulbs cost about the same price, ranging from £1.90 to over £32. However, two H1s are required to do the same job as a single H4.