Hi,
I want to make the Light Level Sensing Circuit as bellow but I don't know how to choose device and value for resistors, Opam.

Could you tell me what values for R1, R2, R3, R4, RF?
What type of opam, transistor that is appropriate for the circuit?
I have just simulated the circuit in proteus with R1=R2=RF = 10K, R3=R4 =330Ω
transistor 2N1711, diode 1N4148, opam 741and the resistor series with LDR is also 10K. It works but I wonder if these values and devices are appropriate to do in real world?
Thanks for help.
P.S In this circuit I want to replace potentiometer by a resistor.

 

Many of the component values are difficult to determine because nothing in your schematic is defined. The values of R3 and TR1 depend on the relay that is used and the value of Vcc. The value of VR1 is determined by what LDR is used. Just by experience I would start with R1 and R2 set to 10K, and RF at 100K and see how it works. I dont think R4 is needed. I would use a 1N4001 for the diode. If you replace the potentiometer with a resistor there will be no way you can adjust the switching level.

 

What particular units of measure for light level are you looking for ?

I have schematics for several photographic light meters...
all indicate which lens f-stop to employ for a given exposure.
based on the " EV " or light value protocol...