From a functional point of view it is a so-called joule thief or vampire torch that only actives in the dark. Specifically, LEDs need 3V to light up but the circuit is powered using only a 1.5V battery. However, when the photo-resistor detects low levels of light intensity the LEDs light up. How is that possible? The circuit has a voltage booster area that increases the voltage to nearly 6V so that it can power both LEDs in series. It does it through an oscillatory behaviour that fills the capacitor with voltage. Further, when the capacitor is charged the transistor comes into play as it releases all the voltage to the LEDs all at once. This process is iterated until the battery is fully discharged. This also means that the lights are not on all the time, but it all happens so fast that it is not visible to the naked eye.