Night Light II
The CdS cell has a characteristic that its resistance increases as the light falling on it becomes darker. One very practical use for a CdS cell is to turn lights or other devices on or off at sunset or sunrise.
Here's a circuit that lights up the LED at night. While you build this project, take a good look at where the CdS cell is placed in the circuit. Do you have any idea why it is placed there instead of at some other point? (If you do, make a note ... because we'll soon find out.)
Now switch power ON and carefully adjust the 50K control until you reach the point where the LED lights.
Once you reach this point, reduce the control volume setting until the LED goes out.
Once you get this project "set" to the right control setting, it lights the LED once the light surrounding your kit dims. You can find a more complex version of this circuit in some street light.