I always have my battery powered lights on when I'm riding on the road, even in the middle of the day. I run a bright red rear light (not flashing 100-200 lumens depending on time of day) and a bright amber or white front light (120 lumen amber during daylight, 200-800 lumen white near sunrise/sunset or when dark). Car drivers are very unaware of their surroundings, any additional indication I can give them to pay attention to me and not hit me is worth it for me. I want my lights to look like drivers expect car lights to look, as that's what they're trained to look for.