h1/h3 light bulb

The H1 gives off an impression of being longer and more slender, and the bulbs both have various bases. The H1 bulb utilizes a P14. 5 base, while the H3 bulb utilizes a PK22s base and has a wire distending from the base.  You can't just switch H1 for H3 and you can't plug a H1 bulb into a H3 fitting.