This Circuit shows a simple biasing method for allowing a Photoresistor to turn on or off an LED. Becouse EveryCircuit does not have photoresistors, the role of a photoresistor is played by a potentiometer. The amount of light received changes the resistance of the photoresistor. You can replace either potentiometer with a photoresistor and use the other potentiometer to adjust the on/off point. If the top one is replaced, the LED turns on when the phtotoresistor receives enough light. If the bottom one is replaced, the light is turned on when the potoresistor looses enough light.