Came up behind a cyclist a couple weeks ago about 3:30 on a sunny afternoon and I spotted his brightly colored jersey at least a mile away. I knew what I was seeing right away as that stretch of road is popular with local cyclists and I'm always on the watch for them. We reached an intersection about the same time and I hung back as I was making a right turn and didn't want to cut him off. It wasn't until I made my turn and got within 15 feet of him that I noticed his red strobe. I was going to say something but he took off across the intersection before I could get his attention. I had my eyes on him the entire time and never saw his strobe until I was literally on top of him, it was pretty much useless. As to night time legality it would depend on your local laws but I run multiple strobes at night and have had several favorable comments from the police and motorists.