The high-beam is designed to light up the road as evenly as possible in front of the car. According to the highway code, driving using the high-beam is only allowed when there is no oncoming traffic which might be
dazzled. In contrast to the dipped beam there are no exactly stipulated light/dark boundaries. Due to the density of the traffic in Western Europe, the high-
beam is not used very often,
this is different in areas like Northern Scandinavia, where the population is much lower, thus, where there is much less traffic.
As shown in the above figure, in parabolic headlights with a two-filament bulb, in contrast the dipped lights, the entire reflector is always used. A paraboloid is the result of curving a parable around its main axis. It only
has one focal point. The beams leading off from this point leave the headlight bundled parallel to each other, basically making the paraboloid reflectors well suited for high-beam. Thereby, in twin headlamp systems
Bilux-bulb (Osram) (with two filaments) the left filament has no reflecting cover. The high-beam can also be generated in a four-headlight system.
|Rougher reflector surface -> weaker reflection.|
In the history of the automobile, the high-beam was around before the dipping lights. This was due to the very low amount of traffic and also the small proportion of night-trips. The switch for changing from high- to low-
beam has also undergone a number of changes. The first switches, e.g., those used for two-wheelers, were mechanical and were built into the headlamp itself, the change-over was done using Bowden-cables or
some sort of linkage mounted on the handlebars.
For a long time, the foot-switch was used in cars, each time it was pressed, one changed from low- to high-beam. The high-beam flasher however, first appeared in a Fiat in 1935, indeed, it would only assert itself
very much later.