I saw this question on a local bicycle discussion list:
Is there a legal limit to how bright a bicycle light can be in the Bay Area measured in lumens?
Equipment requirements for bicycles are addressed in California Vehicle Code 21201. It says only that bicycles operated at night must be equipped with “A lamp emitting a white light that, while the bicycle is in motion, illuminates the highway, sidewalk, or bikeway in front of the bicyclist and is visible from a distance of 300 feet in front and from the sides of the bicycle.”
There’s just a (poorly defined) minimum brightness; no maximum brightness is specified.
In California, almost all traffic laws — including bicycle laws — are regulated at the state law to provide for uniformity. Among the more notable exceptions are sidewalk riding and registration requirements, which may be regulated at the local level.
Do any American states specify anything beyond a minimum brightness for bicycle headlights? Internationally, I know only that the German StVZO law and Dutch DEKRA NL standards limit front light brightness to avoid dazzling people in front of them.