These were gifts I made for friends and family. I'm calling it the Firefly Jar since it looks like a jar of invisible flickering fireflies at night.
This project is a replacement lid for a mason jar. The PCB is 2.5 in diameter with a 55 mm round solar cell on top. This centers perfectly with a standard mason jar and lid collar. The solar cell recharges two 1.2V Ni-MH AAA batteries during the day. At night a P channel MOSFET switches on two candle flicker yellow LED's through a 2.1V LDO voltage regulator. The MOSFET only engages the LED's when the voltage on the solar cell is low and the batteries are above their 0.85V empty state. The LDO voltage regulator is an easy way to ensure a constant LED brightness throughout the life of the batteries.
This would make a good DIY kit since the part count is minimal and all components are through hole.