Coding is my weak point. As such, when I approach projects as such, I start with the BARE MINIMUM necessary to get the thing to show functionality as quickly as possible.
For initial testing, I am simply running the light in the growing enclosure, and measuring the temperature over time. The program that I wrote spits back over serial, comma separated strings of the temperature readings.
To log the data, I'm using the logging feature of putty, saving the entire session to a .CSV file, while putty simply listens to the arduino at 9600 baud. If you have a computer available, this is about the easiest way to store output from your Arduino.