We often talk about light distribution in our blog posts. But what’s behind this concept and what does it mean for drivers?

Everyone knows that high beam provides the best visibility. It’s just that it has one big downside. It dazzles oncoming drivers. That’s why dipped beam was introduced – in the early years of cars – and was designed not to shine its light onto oncoming drivers. The downside of this dipped beam though was that there wasn’t a lot of light left for your own side of the road. The reason was that high beam was simply lowered symmetrically. That’s how symmetrical dipped beam was created. Whatever light reaches the road experts call light distribution.

With increasing traffic, more frequent use of dipped beam as a result and ever increasing speeds, the substantially reduced range started to become annoying. Ultimately it’s unclear who had the brilliant idea of illuminating your own side of the road more than the oncoming side. In any case, the result was asymmetrical dipped beam. The fact is that cars in the US were equipped with it from 1941. Europe had other problems at the time, which meant that most vehicles had their lights blacked out.

Triangular in shape, the light from the car’s headlamp goes up by 15 degrees on the right. This produces asymmetrical dipped beam which shines further towards the right than the left.


Asymmetrical light only arrived in the Old World in 1958. Osram was there from the start with its advanced Bilux lamp. This brand name is still common today for the dual-filament lamp which is actually called R2.In old headlights with real diffusers you can still see the more or less triangular sections which guide the light. Today this effect is created in the reflector, and the headlight cover is clear.

At the end of the 1950s, the light from the R2, which now seems rather modest, brought considerable improvements. On your side of the road the range was now twice as long as on the oncoming side. Many lighting experts therefore consider asymmetrical light distribution to be the most important car light innovation – at least until the introduction of glare-free high beam. This comes with no fixed light distribution anymore. It always throws as much light as possible onto the road, masking out oncoming cars.


Other than that, there are still some vehicles with symmetrical dipped beam. Trams, for instance. And trucks for waste collection and road cleaning. Why’s that? All these vehicles now and then have to and are allowed to go against the normal traffic flow, in other words on the left side in countries with right-hand traffic. Asymmetrical light would then shine directly onto oncoming traffic. That’s also the reason why cars shouldn’t park against the normal traffic flow because they would dazzle other drivers when parking and leaving.

Fog lights, city lights in adaptive lighting systems and daytime running lights are also still symmetrical. The latter even have high-beam distribution. That’s why you’re not allowed to use them after dark.

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