I was wondering this myself, but if car headlights are approaching 3000 lumens, then I really do not have anything to worry about. The other day at the mec in vancouver we were in the bike light section and a guy was looking for a light to see with. I showed him my light, and all the light and motion urban 500 and 300's were out of stock, but they did have a 350 lumen cygolite. He was interested and went to ask a staff member. The staff member told him the 350 lumen light was too bright, it was meant for trail riding and he would get a ticket riding in the city. We were so choked! And it is not the first time I've seen mec staff members try steer people away from bright lights. In fact, they seem to encourage people to buy the cheapest dimmest lights. I've tried many over the years, and all it means is every year I'd have to go and see what's new. Now led technology has improved enough to give one a fairly bright light without all the cables and battery packs.
I've looked it up and there are not legal restrictions except for Germany that I know of. That is ironic considering where the best brightest bike lights come from...

I mostly ride on a rural highway. At night I bike against ferry traffic and it is really hard to see, especially in the rain. I got the nite rider minewt 600 cordless and while it is bright, it is still not bright enough if I am honest. The light just gets absorbed by oncoming traffic and then I still cannot see very well. I do feel a bit sheepish and tend to point the light down to the road, but then I cannot see the road. My husband says my light is not very bright compared to headlights and should not worry.
So, as far as I am concerned, there is no such thing as too bright. If I ride on a mup or come across a pedestrian on the highway I will dim the light or point it down. I have only gotten positive comments from pedestrians and cyclists. The light will not blind you, just don't stare right into it! Those HID headlights that cars have now are so insanely bright! they are legal without restrictions in Canada, so it is getting really hard to tell what is high beam or not. And if cars and suvs can be light up like Las Vegas, why shouldn't a cyclist be using a high powered light? We have to legally follow the rules of the road as if we were vehicles, so we have to see, and be seen.