The dipped headlights are designed for permanent use and may, under no circumstances, particularly on two-lane motorways, dazzle the oncoming traffic. It should light up the road area to approx. 50 meters in front of the vehicle on the drivers side. In the case of asymmetric dipped lights, (see figure 3) the light-cone may shine, from the center to the passenger side, up to 150 meters ahead. The exact maximum of light intensity at headlamp height and at a distance of 25 meters is prescribed by law. At this point, depending on the height of the headlamps, a percentage value is found. If the value of '1%' is found on the casing, the light-beam drops from around a height of 60 cm, by 10 cm every 10 m, thus reaching the ground about 60 meters ahead of the vehicle. This percentage value corresponds to the incline of the light-beam.
Height of headlamps: 0,65 m, length of light cone: 65 m -> 1%
In the case of the Bilux-lamp (two-headlamp system) the dipped headlights only use the front coil. The bottom of the lamp is covered by a mirror. It's rays are only directed to the upper part of the paraboloid reflector. Because it is placed in front of the focus point, the light input- and reflexion angles are somewhat larger. They thus, reach the road surface earlier than the high-beam. In a normal motor car, the beam sinks by about one centimeter per meter.
Asymmetric dipped headlights
The stronger lighting-up of one side of the road is achieved, in older vehicles, by the diffusion glass. This enables one side to work like a lens, and increasingly breaks the light-beam, weakening it towards the side of the road. Diffusion glasses or free-form reflectors are also necessary in a four-headlamp system (see figure 2). In this case, the mirror falls away in the dipped headlights.
The circuit diagram shows the dipped headlights (red), which is operated by the dipped-/high-beam switch in the center. To the left of it, are the parking lights and the number-plate light, on the right are the fog-lamps and a rear fog-light. In Germany, dipped headlamps may be mounted no higher than 1200 mm above the roadsurface (road regulations). This is measured at the highest point of where the beam leaves the headlamp. They must emit white light. Higher placed headlamps, which burn at the same time as the dipped lights are not permitted.
Apart from a light bulb, a reflector which provides for parallel light-beams is also necessary. Earlier, metal-plate was covered by a very thin layer of chrome, nowadays the chrome is applied onto plastic. It shaped like a paraboloid, which one can imagine as a parabola rotating around it's middle-axis. Should it depend on an exact shaping, e.g., as in contact lenses, the basic body is also manufactured through this rotation. Because the reflector works like a mirror, one can assume that the light input- and reflexion angles always remain constant. What is special about this geometric form, is that there is a point, called the focal point, to which all the emitting light in the reflector is aligned parallel. 05/10
Since 2006, in every licenced vehicle in Europe, the changing of a light bulb must be able to be carried out by a layman using the on-board tools and the users manual.