Light Sensor

Here is a sample of a simple Light Sensor using LDR as its sensor and LM741 as the comparator.

When the LDR (Light Dependent Resistor) is illuminated, current passes. The resistance of LDRs are usually very high thus preventing the current to pass. 

*If the light intensity is low LED will lit.

Materials:

R1 660 ohms 1/4W
R2 LDR 10k ohms
R3 100 ohms 1/4W
R4 470 ohms 1/4W
R5 10k omhs 1/4W
R6 1k omhs 1/4W
R7 470 ohms 1/4W
VR1 1k Potentiometer
Comparator LM741
Q1 2n3904 NPN transistor
D1 LED
B1 9v Battery