I have this on my phone, and it really works.
https://play.google.com/store/apps/details?id=jp.ne.hardyinfinity.bluelightfilter.free&hl=en
This is the desktop/laptop version.
http://www.techsupportalert.com/content/reminder-if-you-use-windows-just-get-flux.htm
The blue light emitted from screens can apparently interfere with sleep patterns, if used late at night.
Disclaimer---I haven't tried in on my desktop or laptop yet.