The following circuit is a simple schematic of solar garden light. It charges the battery and light on the LED at dusk, and will be off during daylight. The schematic has 3 transistors. It turns on when the photo resistor fails to detect lights. Its resistance goes very high effectively. THerefore, this would allow the 47k base resistor to turn the transistor on. As the 100n charges, the voltage rises on the base, the transistor will then turn on.