If a car shines its light onto a wall from a few meters away, dipped beam has a surprise in store for some. On the right-hand side both light beams go slightly up. These spikes are not a fault in the headlights, but are known as dipped beam asymmetry.
Apparently there have been drivers in the past who took their car to the garage because the light was not being distributed in a straight line. Hopefully the mechanic explained to them that the increased amount of light on the right of the light beams provides much improved visibility; because with dipped beam on, the headlights illuminate the right-hand side of the road much further than the left. For left-hand traffic it’s the other way round of course. High beam, daytime running lights and fog lights are still symmetrical, by the way.
Asymmetrical dipped beam has already been around in Europe since the late 1950s. In the US, cars even had it almost 20 years earlier. The reason for the introduction was the short range of earlier (symmetrical) low-beam headlights. Their range was at approximately 20 meters – way too short for ever faster traffic. Raising dipped beam altogether was out of the question. Dazzled oncoming drivers wouldn’t have been happy. So headlights were changed in such a way that they only illuminated their own side of the road more brightly, and dipped beam now has a range of 50 meters or more.
Back then irregular light emission was achieved with the help of diffusers that had some areas ribbed differently from the rest. Today reflectors are used to generate the asymmetrical light distribution. The new matrix headlights are a very elegant solution in which individual LEDs illuminate the appropriate places on the road. Modern technology can also eliminate some disadvantages of asymmetrical dipped beam. One is that the long tip on the right in the low beam can dazzle oncoming traffic in some right-hand bends. Cornering lights swivel into the curve and prevent that. Masking the headlight covers when traveling in countries with traffic on the other side of the road also becomes superfluous in some modern headlights.
High-performance lamps such as the Osram Night Breaker Laser deal with asymmetrical dipped beam particularly well. They’ve been specifically optimized for the important areas on your own side of the road.