Light Dependent Resistor(LDR) tolerance problem

[kbtan]

I am designing a solar tracker using 2 LDR and a op-amp as a comparator to compare the light intensity from LDR. Below is my schematic

The problem is the LDR that I bought won't have exactly the same resistance when receive same light. There are some difference on the resistance especially at dark condition. The LDR difference can up to Mohm. while in light condition the difference is only about hundred ohm.
Can anyone help me solve the problem.

Thank You

 

[Audioguru]

LDRs are simple and cheap. They have a wide tolerance and their value changes with temperature change and with age. Sunlight and humidity destroy an LDR in a couple of years. Photo-diodes and photo-transistors are much better.

 

[kbtan]

Sir, how should I use the photodiode as the sensor. Can you give me a refference?

 

[Audioguru]

Google has many articles about photo-diodes. The output level is low so an opamp is used as a preamp.