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How Light Dependant Resistor(LDR) Works? Animation
(Image: Light Dependant Resistor (LDR))
LDRs or Light Dependent Resistors are very
especially in light/dark sensor circuits. Normally the
resistance of an
LDR is very high, sometimes as high as 1000 000 ohms, but when
illuminated with light resistance drops dramatically.
(Image: Working of an LDR in a
This is an example of a light sensor circuit :
When the light level is low the resistance of
is high. This prevents current from flowing to the base of the
transistors. Consequently the LED does not light.
However, when light shines onto the LDR its resistance falls and
flows into the base of the first transistor and then the second
transistor. The LED lights.
resistor can be
turned up or down to increase or decrease resistance, in this
way it can
make the circuit more or less sensitive.