H4 car bulb is a kind of headlight bulb commonly used in cars. They are also called twin-filament bulbs because they have two filaments, one for low beams and one for high beam. H4 bulbs are usually round or oval and have two prongs at the base that go into the headlight assembly. They are designed to provide bright and efficient lighting for the driver. Their lifespan is typically around 1000 hours, but this may vary with usage and lamp quality.

H4 bulbs come in a variety of styles. Halogen bulbs, the most common type of H4 bulb, use a filament heated by an electric current to produce light. They are relatively cheap and widely available.

HID bulbs use a high-voltage arc to produce light, while xenon bulbs, also known as HIDs, use a gas-discharge lamp that produces a bright white light. Both types of bulbs are brighter and more energy efficient than halogen bulbs, but they can be more expensive.

LED light bulbs use semiconductor materials to produce light. They are very energy efficient and long-lasting, but they may be more expensive than other types of H4 bulbs.

Plasma bulbs use plasma-based technology to produce brighter, whiter light than halogen bulbs. They are more energy efficient and last longer than halogen lights, but can be more expensive.