What is the function of the Light dependent resistor?

Answer 1

The resistance of LDR increases when light is not available (or is limited). And the resistance drops when Light is abundant.

This principle can be used in proximity detectors where one or more light source(s) is/are active. When a person / object comes in proximity of the source, the light gets reflected from the object-surface & can now be received by LDR. So due to proximity of the object, resistance of LDR changes - this can be used to trigger different actions like open the door, trigger a motor. Fire an alarm. etc.
Resistance of LDR varies according to intensity of incident light over it,It is used in street light to detect day/night and turn on/off the street light automatically

Answer 2

A photoresistor or light dependent resistor or cadmium sulfide (CdS) cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referenced as a photoconductor. A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

Answer 3

A LDR or light dependant resistor is a resistor that works when light is not shining on it, so if there is light on it it will not resist a current, you can also get them to work the other way.