H4 and H7 are types of halogen bulbs commonly used in automotive headlight systems. Here are some differences between the two:

Light output: H4 bulbs have two filaments, one for the low beam and one for the high beam, while H7 bulbs have only one filament for the low beam. This means that H4 bulbs can provide both low and high beams without the need for a separate bulb, while H7 bulbs require a separate bulb for the high beam.

Wiring: Because H4 bulbs have two filaments, they require a different wiring setup than H7 bulbs. H4 bulbs require three wires, while H7 bulbs only require two.

Shape and size: H4 and H7 bulbs have different shapes and sizes, so they are not interchangeable. H4 bulbs have a P43t base and are larger than H7 bulbs, which have a PX26d base.

Compatibility: The type of bulb used in a vehicle's headlight system is determined by the manufacturer, so it is important to check the owner's manual or consult with a qualified mechanic to ensure that the correct bulb is used.

Beam pattern: Because H4 bulbs have two filaments, they can provide a different beam pattern than H7 bulbs, which only have one filament. The specific beam pattern and brightness will vary depending on the specific bulb and vehicle.

Overall, the main differences between H4 and H7 bulbs are the number of filaments, wiring, shape and size, and compatibility with specific vehicles. It is important to use the correct type of bulb for a vehicle's headlight system to ensure proper functionality and compliance with safety regulations.