A light sensor built for Raspberry Pi and Adafruit's TSL2561 Lumosity Sensor.
If you want to use this code, get your Raspberry Pi and Adafruit's TSL2561 (http://www.adafruit.com/products/439). Then, make an account on Cosm.com and paste your API key and feed number so that you can record your data!
NOTE: After I posted this code I realized that Cosm is now called Xively, and they've probably changed their API to make this not work. At some point I may get around to implementing the new Xively API, but for now you will need to change the request code if you want to use it.