What is irradiance? What is the general relation between irradiance and current for photo resistor?
wut?
I can answer the first question: http://en.wikipedia.org/wiki/Irradiance 
You do know this is a web tech forum, don’t you? It may not be the best place to ask a question like that. Why do you want to know, anyway? Is it part of a course, or what?
Thanks