I assume you are talking about taillights. In that case, the new Planet Bike Superflash is hard to beat. It is quite powerful and has a somewhat variable flashing rate. I rode with one of these in flashing mode this November and December when part of my commute was dead into the rising sun. If they don't see you with it, they'll run into a bus. Battery life is also very good, so you shouldn't ruin your battery budget either.