I've been playing with a micro and a photodiode for use in a DIY camera project. I'm using a Hamamatsu s7183 photodiode ic. It is amplified so the circuit is simple. Just hand a resistor off be end ofit and measure be voltage drop across it. The resistor size will dictate the sensitivity of the system. It will work just like your temperature probe program I think.
Couldabin, I have seen something that is very close to what you are working on at http://roamingdrone.wordpress.com/20...or-time-lapse/ and was considering something like it myself. It also uses the TSL230R as was suggested here.
Now that is a very cool solution.