Just found this thread while trying to figure out how to calculate lux with a cheap light meter I bought. NO data sheet available. I've checked the resistance of the photoresistor, and it's 20k ohms when dark, and close to 200 ohms with a bright flashlight. Attempting to use the code above, it seems that one flaw is that the voltage is backwards. The lux value goes down when light is added, and up when light is taken away. Swapping it so that it's the difference from 5 volts of the volts value (volts = 5.0 - volts), gets pretty close, but it's still not right. I have a cheap lux meter that I used to try to calculate a lux:ohms table. It's crazy how NOT linear the photoresistor is. While darkness is 20k ohms, 41 lux is ~6k ohms. 14k ohms for 40lux is certainly not linear to the max of 155 ohms at 110,000 lux.

The question is, might this just have to do with this specific photoresistor, or is it common for them to not have linear values like that? I have a TEMT6000 on order, and really want to be able to calculate lux values. Maybe my cheap lux meter is, um... cheap.