I and other members of my rowing club often row in the dark when it is difficult to see the navigation buoys which can easily cause a narrow rowing shell to flip. It would be nice to attach lights to the top of the buoys. Available solar powered lights turn on when it is dark but do not have enough energy to stay on all night.
We especially need light for early morning rows starting at 5:30AM. Since there is no way to modify the commercial offerings, I needed to build one of my own. This light turns on when it is dark but only at certain times so energy isn't used during non-rowing hours. The light's waterproof housing contains a solar cell, Arduino, real time clock, LiPo battery, battery charger, LED driver and bright LEDs (red and green versions) on four sides.