The resistance of an LDR falls as it is exposed to more light. The light-sensitive material(2) is arranged in a pattern between the two terminals(1) and(3),to increase the effect by having as much surface area as possible.
Light-dependent resistors make use of the fact that some semiconductor materials react to light, having a very high resistance in the dark,but lower resistance as they are exposed to more and more light.
An LDR consists therefore of two contact plates,(1) and(3),connected to the terminals emergine from the bottom of the LDR, separated by a pattern to light-sensitive semiconductor material(2).The shape of the pattern ensures that there is a large area of semiconductor exposed to any light which may pass through the enclosing glass cover.The semiconductor material provides the light-dependent resistance between the two terminals.
The graph shows how a typical LDR responds tp changes in light level(the Lux is the unit of light).At point A,the light level is very low,such as in moonlight,and the LDR resistance is about 1 Megohm. More light reduces the resistance until at point B, bright sunlight, the resistance could be as low as 100 ohms.