NiteRider

It's a back flasher light. Not a high-tech thing (i.e. like Di2 or carbon wheels). But it works. Easy to mount on my bikes - I have multiple bikes (Cervelo S5 - aero seat post and a Caledonia (standard round 27.2 seat post). Battery lasts a long time. Sometimes I forget to charge it and I am amazed that it lasted for that entire ride. It's really bright. In the morning when it's dark, I turn on the NiteRider Sentry Aero 260 Rear Light, the light hurts my eyes because it's so bright.

I would like to give this light 5 stars like everyone else, but the mount strap is too short. I was able to stretch the strap and get it to hook into the first hole; but it is too tight and I expect it to break sooner rather than later.

Also, the the base of the strap which attaches the strap to the light is curved on the inside, and the back of Specialized seatpost is flat.

I cannot recommend this light for Specialized road bikes.

Have NR 1000 light on bike, bought second NR Lumina Micro 900 to mount on helmet for nighttime Fat Biking in Alaska, its nice to see moose before you get stomped. Have been impressed with battery life even at extremely cold temperatures. Blinking feature is nice for extra visibility along roads in the daylight.

This light is so powerful during the day. My initial buy was the Exposure MK3, but I read plenty of reviews on it and decided to pass. My second was the Cygolite hypershot. But read too many mix reviews on the durability of it. I decided to go with niteride because many ppl recommended the brand to me on Reddit for long cycling rides during the day. I needed a rear light that would last 6-9hrs. This thing is extremely powerful and also battery is very efficient depending on what setting you have it.