We had a cyclist killed on Sunset Blvd. some years ago, and the report included the fact that his rear reflector was subsequently tested by the police and found to be visible for less than the legally-required distance. Pretty sure it was a CPSC-approved reflector, as the bike was a Huffy. Actual real-world performance is what will likely count in court if the lawyers are looking to get their client off the hook, I think. DOT-approved reflective tape is a safe bet, e.g. DOT Class II (or better).