Quite a few people in our biking club have this, or a light similar to it, on their bike’s seat post. Most of their bikes have the light set in an intermittent quick flash mode. Were it not for the instruction sheet included with Yinstr’s brake light, I doubt I would have known how to change its lighting modes.The light is turned on by a 2-second press of its button switch located at the center of its red lens. Switching lighting modes is done with the same button. Once the light is on, the 4 remaining modes can be accessed sequentially with a quick push of the center lens button. Mode 1 has the light continuously flashing. Mode 2 flashes slowly in what the instructions call a breathing fashion. Mode 3, the one I favor, sets up a spaced double flash. And finally, mode 4 is a rhythm flash, which seems random to me. There is a mode 5. It just has the light continuously in the on position, the same as when the light is first turned on, so I didn’t consider it a mode. Battery life is claimed to be between 10 and 26 hours, depending on the lighting mode chosen, with the always-on being the lowest and the double flash being the longest. I charged the light up fully before mounting it on my bike and haven’t used it long enough to validate its instruction’s battery life claims. Charging is accomplished using the included USB C cable. The light’s charging port is evident when detached from its base.I removed the light from its mounting base to make attaching the base to my seat post easier. The aluminum light and base bodies are joined using shallow, narrow threads. Fortunately, I didn’t cross-thread the two, but it would have been easy to do had I not been careful about their thread alignment. The light’s base is attached to the seat post using its attached rubber band. The band has a hook that clips into increasingly tighter holes in the band. I used the first hole initially for a snug fit but then decided to stretch the band to its second hole for a tight fit. When mounted, the light base rests at an angle to counter the inherent rear-facing angle of a bike’s seat post.Most of my riding is in daylight, so I set the light to its double-flash mode. The flashing and light’s brightness are enough to get me noticed by auto drivers as they approach my bike on the road, which is the reason I got it.

The Yinstr bike is an intelligent light with a thoughtful design.   The bike light weighs 1.6 ounces.   The bottom length is 2.0625 inches. The top length is 1.8125 inches. The top width is 1.375 inches. The bottom width is 1.25 inches.To power up and turn off the light I pressed the button in the center of light. It is a hold press for 2 seconds.  To switch through the different light patterns I pushed the button in one time.  There are 5 different light patterns of the Yinstr bike light. The light patterns are flashing, breathing, which is a fade in and out,  double flashing, which is red then green, rhythm flashing, which is similar to strobing, and solid, which is always on. Double flashing is my go to pattern, since green is the most visible to the human eye at night. The approximate battery life of each of the modes is 14 hours for flashing, 13 hours for breathing, 26 hours for double flashing, 8.5 hours for rhythm. The light attaches easily with the fixed rubber strap. Simply wrap it around the seat post and fasten it inside the holes like a waist belt.  I was perplexed at first how to charge this light.  There is not the usual rubber door flap.  Then I thought maybe it unscrews. Sure enough, the  bottom of the light unscrews from the top concealing and protecting the type C usb hole.  I found this a thought full design, not only is the usb hole 100% protected from the elements, the omission of the rubber door means it will always remain so and not break off. In addition, the rubber strap never has to be taken off the seat post to charge the light, since the portion with the usb C hole unscrews from the bottom. I also prefer the strap design attachment, since it feels more secure and easy to connect to the seat post. When the bike light senses that it is dark out along with the motion (vibration) of the bike the light automatically will turn on.  Then, when the bike is stopped the light gets brighter for two seconds like how when a vehicle's brakes are applied the brake lights get brighter. I never heard of a rear bike light doing that before now.  If the light is turned on in the daylight it will only remain on for 40 seconds. Therefore, if for some reason you wanted to use a rear bike light in the daytime this one would not work.The only thing that needs improving is the instruction manual. The verbage was a little confusing to me at times.  The bigger issue is that nowhere did it say or show where the usb C charging hole was located. I did a test to see at night to see if a light was shined on it, if the light would still reflect if not turned on.   Just in case the battery ever died before I remembered to charge it, I wanted to make sure there was still some kind of illumination going on and there was. One of the pictures reflects this. One picture shows the transition of the double flashing with the green and part of the red light gradienting in.