We found these LED devices on the promenade sea wall by Blackpool Pleasure Beach. They seemed to be worked by small solar panels. The LED I posted about a couple of weeks ago was running 0.02A at 1.5V which is a power of 0.03W or 30mW. There are 6 LEDs so let's estimate 180mW. In peak sunlight, the Sun reaches about 1600 Watts per square metre. On a dull day in Winter maybe 800 Watts per square metre. The solar cell can't be bigger than 2cm x 3cm or 6 x 10^-4 square metres. That would then generate 0.48W in Winter. But the cell doesn't drive the LEDs directly because you want them to come on after dark. It must charge a battery. Then we'd be into calculating Amphours charging versus Amphours discharging.
