Originally Posted by
tractorlegs
It simply isn't true in the real world. First, no one is ever rendered blind by a bicycle light. Our terminology "blinding light" or "drivers are blinded" is merely a colorful use of terminology that never really means that their eyesight is completely removed. No more than the term "blowing your mind" means that their brain blows up. Lights are bright, they are distracting, and sometimes you cannot see what is immediately behind the light or around the light, however you are still able to see everything else around you. The only way a bike light can completely remove your eyesight is if it is right in your face. Then the last part of your statement - that people automatically steer into the bright light - is not true in the real world. If that happened, most of us would be in emergency rooms or dead as a doornail. If it were true, most cars on the highway would be having head-on collisions at night because of each others headlights. In the real world it just doesn't happen.
I came across this review
http://www.visualexpert.com/Resources/motheffect.html which concludes "The "moth-effect" is a myth in one sense and reality in another. The idea that drivers may steer off the road when they fixate flashing lights is likely correct, but they are not drawn to the lights like moths to a flame. Rather, they inadvertently steer rightward, which may or may not take them into collision with the roadside vehicle." They also note that '
Neither study, however, employed bright lights, so it is unlikely that the "moth-effect" results from an innate phototaxis.'
So it sounds like you're both right.
I can tell you anecdotaly that I can be completely blinded by an approaching bike light that comes within a few feet, with impaired vision for two or three seconds. It's not a literal physiological blindness, as you point out, but a temporary loss of the ability to see anything in the direction of travel.