I have daylight balanced bulbs at home so I'm using the Daylight setting. I thought that I was supposed to match them up. Or is it just a preference of color temperature? It would be nice if the UI included icons for the type of bulb so they are easily identified if for instance you don't know what a halogen bulb looks like.

in the night, while the lights in the room are on, open something white in your computer (i.e. a document). Take a piece of white paper and compare it to the white document on the screen. The correct setting is the one in which the background ("white") of the document on the screen looks most similar to the document in real life.

Cheers.

If you want to improve your sleeping you should expose yourself to less blue light before bedtime.