I friend rides very often on her bike in the dark and has yet to find a good light to be visible (from all sides).
Many things for that purpose are sold but most of them are very dim.
LED strips could be a solution. Some are 5v powered so they could be connected to a small 5v 18650 power bank.
Any runtime exceeding 1 hour is good.
A strobe light effect would greatly improve visibility.
I think green is the most visible to the human eye.
I looked on AliExpress and found several products that may fit (most) the above mentioned requirements.
Finding the lumen output of those strips is problematic.
Assuming a 3500mAh powerbank, reduced capacity due to freezing temps, loses, etc, I think to get an hour runtime the strip should draw about 5-7 watts.
I’m aware many of the strips can be cut to length and with that the powerdraw is determined. But I want the strip to be about 1 foot long.
I’ve yet to find that.
Summary.
I’m looking for a 5v, 6W, 1ft long, strobing, (green) waterproof LED strip.
BTW a COB light that can be stuck on a backpack is also an good option.