IIHS

IIHS (Insurance Institute for Highway Safety) also created a testing method, but it is far more documented and scientific.

Their testing includes general metrics like "visibility" and "glare." Visibility is defined as the distance where a light shines 5 lux, but the headlight has to keep that object illuminated as the vehicle approaches.

The testing is performed with the vehicle in motion.

The testing also includes factors like "pitch correction" of output, as they have determined that lights shining at other drivers, especially over hills, is a concern. 

More information (optional): https://www.iihs.org/media/0e823704-32d1-4500-b095-15d064d824a7/ZJciYw/