With F.lux coming to the iOS platform, I figured I'd remind everyone that F.lux exists! Basically it changes the color temperature of your device to be easier on your eyes as it gets brighter or darker, often based on the time of day and where you are located.
Here's the
link for iOS (you have to be jailbroken)
Here's
the link for anyone on Windows, Mac, or Linux
If your eyes ever get tired or start hurting late at night, this is a must-install application. It's almost painful for me to a non-temperature adjusted screen after looking at my computer in the evenings. Plus, my eyes never ache when I head to bed.