I haven't read up on the laws concerning it, but I've been using flashing lights on both the front (white) and rear (red) for the past 20 years here in California. None of the lights is blindingly bright, just bright enough to identify me to vehicles. Plenty of cops have seen me, and I've never been stopped. Most of this has been in the early morning when there are very few cars on the roads, and there are plenty of others on bicycles at that time without lights, so I'm not really a problem.