cklim85:
Thank you for your advice. Based on the chart I find out that the formula is y = 1/2(x) + 0. Please correct me if I'm wrong.
I agree. So lux = 2 * microamps.
float volts = analogRead() * 5.0 / 1024.0;
float amps = volts / 10000.0; // across 10,000 Ohms
float microamps = amps * 1000000;
float lux = microamps * 2.0;
Or to mash it all together:
float lux = analogRead() * 0.9765625; // 1000/1024
This should give you a value between 0 and 1000 lux.