Does the US even regulate headlight brightness and function?
Nearly everything about vehicles has US federal and state regulation. Headlight regulations being stricter in the US are why US versions of European cars up until about the 1980s had different headlights than their home markets.
49 CFR § 393, FMVSS 108 and a crapload of other regulations and regulatory interpretations. In general, these make IRS instructions seem a marvel of clarity.
FMVSS-108 S5.5.11(a) talks about brightness.