For those that aren't aware, there's tools to help with this.

    f.lux    | Windows, OS X, iOS (jailbreak needed) | http://stereopsis.com/flux/
    Redshift | Linux, Windows (experimental)         | http://jonls.dk/redshift/
    Lux      | Android                               | https://play.google.com/store/apps/details?id=com.vito.lux

Lux isn't as nice as the others because it doesn't change colour temperature, it just puts a red/brown overlay over the screen. AFAIK there's no way to change the screen's colour temperature in Android.