Photoresistors
A photoresistor is a device that is very sensitive to light or illuminance. Based on the presence of brightness in an ambient environment, the value of resistance can go up or down. This device helps control the circuits to switch on or off based on light sensitivity. For example, in the street light circuit, the lights should be turned on at night and turned off in the daytime. The working mechanism of a photoresistor is such that the resistance drops to a few Ohms when the illuminance is high and the resistance rises to higher values when the illuminance is low.
A photoresistor is also known as a photocell, conductive photocell, or Light-Dependent Resistor (LDR). In Figure 9.4, a symbolic representation of a photoresistor is shown:
Figure 9.4 – A symbolic representation of a photoresistor with a light-sensitive surface (courtesy: https://en.wikipedia.org/wiki/Photoresistor)
On the left-hand side of the diagram, the two arrows indicate...
