The QuantifiedSelf forum recently had an interesting thread on how to track light exposure. By collecting light data one can search for correlations with mood, stress, weight, activity and sleep. This could be helpful for several different purposes.

1. Time Spent Outside
2. Vitamin D Exposure
3. UV Exposure
4. Light Color Temperature (circadian rhythms)

The following hardware and apps were suggested for light tracking:

1. SunSprite – Personal Light Tracker
2. dMinder – Helps to track and manage vitamin D. Calculates ideal duration to be outside based on location, time of year, personal attributes (height, weight and skin type) and provides a stop watch.
3. Life Cycle App – GPS tracking provides breakdown of travel, home, work, etc.
4. SunFriend –  Stand alone bracelet