Hi, this circuit is a solar garden lamp, It charge a battery during the day and turn a light on during the night, using the same solar panel as a sensor .
The circuit can operate with a 3.6V Lipo but it also works with more or less voltage, in schematic is there a photovoltaic generator at about 4V, a low-loss Schottky diode 1n5817 for example, a Lipo cell (or Li - ion) and a led.
If you want to control more led you can follow these circuits, the circuit works well with crystalline solar panel, amorphous need 100k in parallel.
The battery is self protected from discharge because a white led can't turn on with less than about 3V, and it's overcharge protected because the solar panel is about 4V, and the maximum battery voltage is about 4,2V.
I hope you like it.