During the 1900’s, the United States DOT was completely obsessed with standard headlamps. DOT-legal headlamps had to shine light in the sky as well as on the road, because road signs in America are typically unlit. They’re terrible in fog as a result, and also can’t be particularly bright because of the risk of blinding other road users. European dip-beams, in comparison, have a sharp cutoff, are better in fog, and can be brighter without blinding other road users.
Until 1983, every car and motorcycle sold in America had to have non-replaceable bulbs and standard shapes, like 7” or 5” circles, or 8” rectangles. Everything from pickup trucks to BMW motorcycles had the same poor headlamps. After 1983, the United States DOT allowed non-standard, aerodynamic headlamps to be used, and manufacturers were then able to have the same styling for headlamps in both the United States and Europe. The lighting requirements remained the same, however, and DOT continued to allow a significant amount of scatter in the beam pattern—so drivers and riders in the United States have been stuck with poor illumination and messy beam patterns for years.
There is an upside to having many years of standardization. Some European cars and motorcycles had the same styling as their American brethren, and so needed European-spec headlamps. These standard-sizes are much cheaper than the European versions of fancier aerodynamic American headlights.
Rallylights.com carries a full range of standard size ECE (European) headlights, which make a great upgrade to any bike with standard-size DOT headlamps. The assymetrical low-beam and powerful high-beam really make a difference when driving at night—we recently put a 200mm Hella ECE lamp on one of our motorbikes and were blown away by the difference it made. ECE lights aren’t legal in the United States but we’ve never heard of anyone getting ticked for using them.
There are lots of good lights at rallylights.com