Just to be clear from the beginning: we’re talking about dynamic cornering lights. In other words, a technology where the headlights follow the steering movement. It’s easily confused with static cornering lights which only provide a bit more illumination at intersections and turnoffs. Their range is limited as they now almost exclusively come out of fog lights.
Real cornering lights have a far greater range. In most systems, both dipped beam and high beam swivel. This is particularly effective in long, drawn-out curves, so mainly on country roads and highways. And again, especially in right-hand bends. Why’s that? Well, if the road leads to the right, conventional headlights – i.e. those without cornering light – dazzle oncoming traffic more. That’s because of asymmetrical dipped beam which illuminates the right side of the road more. For left-hand traffic it’s the other way around, of course, and there’s then a glare problem for left-hand bends. So in right-hand bends, for example, this stronger part of the light distribution moves toward the middle of the road or even to the left – into oncoming traffic. That’s not the case with dynamic cornering lights. They at least partially follow the layout of the road and illuminate the curve the way they do when you drive straight on.
Swiveling only in darkness
At least if the curve is not too tight. Because the headlights are only allowed to follow the steering movement by up to 15 degrees. But then this angle is ideal for curve radiuses on country roads. For a number of good reasons, regulations don’t allow major swivel movements. Hectic steering wheel movements would create irritating effects from the lights. Or the light could suddenly completely disappear from the driver’s field of vision if, for example, major corrections are necessary on icy roads.
There are other restrictions for which there are also logical reasons. For example that the headlights don’t move when the car is stationary. They also need to return to their starting position if the car stops with its wheels turned. Both these things prevent the light from accidentally shining toward oncoming traffic.
Without it being mandatory, most dynamic cornering light systems are controlled in such a way that the headlights only move in darkness. After all, if you use the main headlights as daytime running lights you don’t need cornering lights. A twilight sensor ensures that the lights don’t swivel, reducing wear and tear of the mechanism.