In order to ensure driving safety, the driver should be able to identify any obstacles on the road within 100m before the car. The illumination distance of automobile high beam is required to be greater than 100m. This figure is based on the speed of the car. As the speed of modern cars increases, the requirement of lighting distance will increase. The lighting distance of the car light is about 50m. The requirements of the position are mainly to illuminate the whole road within the illumination distance and not to deviate from the road at two points.

2. Headlight anti-glare requirement

Car headlight should have prevent blinding device, lest the driver of opposite car is dazzled when two cars meet at night and bring about traffic accident. Used at night when two cars pass, the beam tilts downward to illuminate the road 50 meters in front of the car, avoiding the glare of oncoming drivers.

3. Requirements for luminance intensity of headlamps

The far-light emission intensity of in-use vehicles is: two-light system not less than 15000CD (KANDRA), four-light system not less than 12000CD (KANDRA) : the far-light emission intensity of newly registered vehicles is: two-light system not less than 18000CD (KANDRA), four-light system not less than 15000CD (KANDRA).

With the development of high speed vehicle, some countries began to try out three beam system. The three - beam system is high - speed far - light, high - speed short - light and short - light. When driving on the highway, use high speed high light; When driving on a road without oncoming traffic or when meeting on a freeway, use the shortcut light when there is oncoming traffic or running in the city.