Which car lights should drivers use in fog? First and foremost, their low beam headlights – parking lights as well as daytime running lights are unsuitable. Only intended to indicate the presence of a vehicle, parking lights are simply too weak to properly illuminate the road. Although brighter, daytime running lights have the same strong self-dazzling effect as high beam headlights – and we are all familiar with the impenetrable white wall these create in foggy conditions.
In addition to the low beam highlights, we can also switch on the fog lights of course. In this context, the phrase “in addition to” is key. The formerly popular idea of using fog lights together with parking lights is now completely outdated. Although this combination remains a legal one, with the factory-installed fog lights in modern cars it doesn’t deliver a sufficient amount of light onto the road. Unlike the true auxiliary headlamps for fog, those we are familiar with from years gone by, most fog lights installed in today’s new vehicles are not much more than design features for the front apron. What’s more, their use as turning lights often takes priority over any fog-related functionality. Fog lights of this kind provide width of illumination only, but this can still be extremely useful in foggy conditions. They make it easier to identify the edges of the road and provide better illumination at junctions. When it comes to long-range visibility, however, the low beam headlights remain the vehicle’s mainstay.
There’s also a popular myth about the low positioning of fog lights. According to this old wives’ tale, they are installed so low down to enable them to shine below the level at which the fog starts – allegedly tens of centimeters above the road. If this were true, we could eliminate the problem completely by politely asking the fog to move its starting point a few meters higher! Joking aside, the true reason why fog lights are installed low down on the vehicle is to keep reflections from water droplets as far as possible out of the driver’s line of sight. As we were all taught at school, the angle of incidence is equal to the angle of reflection. Theoretically, this would mean that light from fog lights is only reflected into areas above the windshield. Unfortunately, fog doesn’t seem to adhere to theoretical rules, and fog lights do cause a limited amount of glare.
Germany and many other countries don’t permit high beam headlights to be used in combination with fog lights. A few countries go even farther, and demand that a car’s electrical system explicitly prevents parallel use of these lights. But even where it’s legally possible, the combination makes no sense at all. The rear fog light is also frequently misused. Many drivers activate them at the first hint of mist, but they should really only be switched on when the fog becomes dangerously thick. In clearer conditions, they cause serious glare for any drivers behind the offending vehicle.