If the FMVSS has a spec for viewing angle or sweep angle or reflector angle every automaker is flat out ignoring it. Compare the the backup lights on a 99-11 crown vic with chevy truck or a ford escort, the vic has the largest reflector area and best angle of projection. Both the chevy and escort have the smallest reflector area and the poorest angle of projection. My daughter has a 97 escort and with stock lights are practically useless to see behind the vehicle. I got her some 50w high power led lites and it was an improvement, but with the small recessed reflector, seeing off to either side of the vehicle was not much better. A couple of weeks ago I nearly got backed into by a BMW, he was backing out of a parking space beside me as I was waiting for the guy in front of me to move. I could not tell his backup lites where on until he was almost perpendicular to me. They where inboard of the corner of the car and flush mounted with a very small reflector/lens.Viewing angle of probably less than 45 degrees.
I'm ok with backup lites, ruuning lites, turn signals and drl lamps as led, but led headlights are not there yet even in projector housings. There is almost always stray light from aftermarket led headlamps. Aftermarket led lamp makers can say they are dot approved, but as they don't submit the actual lamp to the dot for testing, they just submit a testing report saying it's compliant if they even go that far. There are led headlamps that are compliant, but they have been engineered and tested by the individual automakers themselves.