Today we created a breadboard circuit closed via a push button switch - power was USB fed through the USB power supply. I used a photoresistor to create a "normally on" switch which disconnected the circuit when light was completely blocked. I decided to 'experiment' with a 9V battery with a regulator as a power supply instead of the USB power we tried in class.
I used a photoresistor to create a switch - the circuit is connected to power when the photoresistor is exposed to light. I chose this as my switch because I have an affinity for light as a filmmaker.
It would be interesting to create the inverse affect and have the photoresistor's light input be what causes the LED to dim for a reverse intuitive effect - to turn the light sensitive resistor into a switch when light is blocked.