I got these bike lights because they said they were 400 lumens - much brighter than my last set, which has been slowly dying. I was a little worried because only the front one was rated at 400 lumens, and I'm more worried about vehicles coming up behind me than those coming toward me. I still don't know how many lumens the back one is, but it's bright enough, so I'm very thankful for that!The two lights seem to be completely different yet put together into one package - they don't even have the same user's manual or the same terminology between the user's manuals. They don't look alike and they don't attach to the bike in the same way.The front light attaches via a little clamp that can be twisted smaller (it does fit snugly around my narrow handlebars, but it would be even better on slightly thicker handlebars). It can swivel 360 degrees while attached to the bike, so that's a very nice feature. The front light has 5 modes - 1) sidelights (yellow), 2) half-brightness solid, 3) full-brightness solid, 4) flickering/blinking at full brightness and sidelights, and 5) an automatic sensor that adapts to current light conditions (indicated by blue around the power button). I've only used the flickering mode, but it works well. The thing I like most about it is that it's bright but not blinding - I hate it when I can't see bikers while I'm driving, but I almost hate it more when their flashing lights are so bright it blinds me and I'm as likely as not to cause an accident because I can't see anything, including them!The back light attaches to the seat post via a rubber strap. I'm not sure how durable the rubber strap will be in the long run, but so far so good and it hasn't slipped, even when I was riding on a rough trail. The back light also has 5 modes - 1) solid white, 2) flickering white, 3) solid red, 4) flashing red, and 5) red and white flickering/flashing. I've always used the fifth mode and it's quite visible, especially considering how small the back light is (actually, I got two sets, and I follow the person with the other set of lights - so I'm very familiar with how visible the back lights are!)Overall, I'm very happy with this purchase so far. The first USB charge hasn't run out yet, so I know they work on flashing for well more than 2.5 hours, which is about all I've used it for at this point.