There used to be strict lighting equipment and usage standards that all cars and drivers had to follow.  The first (and for a long time, only) crack in the dam was the new rectangular headlight bulbs in the early '70s.  But other than the newly allowed shape, the rules didn't change.  

Now with the advent of LED vehicle lighting, the design is whatevah can.  Make your lights look like evil shark eyes (or teeth).  A spectrum as blue as you can get away with.  Improperly aimed and focused (as the study demonstrates) for actual safe driving; way too bright at least half the time, set at a bad height -- for the sake of design, not safety.

Why?  Because regulators are letting 'em get away with it. Gotta fix that.

Used to be that cars could have four headlights, but the extra two were separate high-beams and were illegal to use when following other cars closely.  Suddenly the extra two are down low like foglights, big and bright as headlights and all four are always on.  Wassupwidat!