The H4 car bulb is used for headlights, it contains two filaments, and you can choose a high beam and low beam in one bulb. So if your car is suitable for H4, you only need one set of bulbs to achieve the effect of high beam and low beam. If using other types of headlights, you will need to purchase 2 sets, one for high beam and one for low beam.

　　This bulb has a three-prong attachment on the harness which makes it unique among other bulbs such as H1, and H7... having 2 prongs on the base. Therefore, they are easier to identify.

　　The H4 bulb was originally invented for racing. However, for decades its use was mostly limited to European cars. In the US, H4 bulbs are popular on motorcycles, but cannot be used in cars or trucks due to legal restrictions requiring sealed headlights.

　　Even with these restrictions lifted, H4 bulbs are still banned by U.S. regulators. Twin-filament bulbs are not precise enough to meet the beam pattern limitations of US headlights, as they can easily point upwards and blind oncoming traffic.

　　Therefore, a replacement bulb called the HB2 or 9003 was developed. This can confuse consumers. The H4, HB2, and 9003 are essentially the same bulb and can be used interchangeably. Many bulbs that meet this specification will have all three labels on the packaging.

　　Haining Suez Car Lights Co., Ltd is an LED car headlights supplier, the main products are H7 car bulbs, etc. Welcome to consult!