The other day, in the parking lot of a large auto supply store, I spotted a man standing in front of his sporty mid-range vehicle gazing in rapture at the violet-colored light of his headlamps. He looked overjoyed – presumably with the recent purchase and installation of his new lamps.
I would not have been looking quite so thrilled in his situation, because if you’re standing up straight just three or four meters from the hood of your car, you shouldn’t be able to see much of the light at all. After all, that light should be on the road and not in the region above the headlamps. Everything shining upwards is really lost light. Engineers call it “stray light” and try to eliminate it as much as possible.
The light required and permitted on the road is very precisely defined. The low beams, which we use over 95 percent of the time, illuminate the right side of the road much more extensively than those parts of the roadway that are closer to the center strip and oncoming traffic. With an asymmetrical beam pattern, as it is known, it ensures that the driver can discern pedestrians or signs on the side of the road as soon as possible. What’s more, the irregular shape of the beam prevents the light from dazzling oncoming drivers.
Like all lighting specialists, I make sure not to judge the quality of headlamps or lamps by how brightly they light up the ground immediately in front of a car. The engineers at Osram do all they can to concentrate as much light as possible at the far point, i.e. at the farthest reach of the low beams, or about 65 meters from the front bumper. Less brightness directly in front of a car thus translates into greater visual range, provided that the lamps are of good quality.
Incidentally, the engineers do allow a little bit of light to stray upwards, but not to please the man in front of the auto supply store. Without a bit of stray light, we would no longer be able to see signs at close range as well as we should.