The 5252F integrated circuit does several things. It charges the 1.2 volt battery during the day, using power from the 2.5 volt solar cell. It detects when the solar cell is in the dark, and starts up the circuit inside that boosts the 1.2 volts from the battery to over 3 volts, and sends that to the LED.
The output voltage is pulsed.
The current is limited by the L1 inductor, 330 microHenrys will allow 8 milliamperes to go into the LED. reducing the size of the inductor to 270 microHenrys will give 10 milliamperes.
Garden Light Schematic 5252F