If you are anything like me and spends a good amount of time on computer, your eyes may say you soon that "Hey! it's fantastic. Give me some comfort or else I'll take yours". You may soon face dry-eyes or sleeping dis-orders. Let's take some precautions to save them.
Now I'm not gonna discuss something like don't stare without blinking your eyes or maintain some distance from monitor, but here is a way to optimize your monitors brightness automatically according to the time-of-the-day and temperature.
Redshift adjusts the color temperature of your screen according to your surroundings. This may help your eyes hurt less if you are working in front of the screen at night.
To install it in Ubuntu:

sudo add-apt-repository ppa:jonls/redshift-ppa
sudo apt-get update && sudo apt-get install redshift

To start the application, first find the coordinates of your location (lat:long). Then

redshift -l lat:long (eg: redshift -l 17.033:55.20)

For latest version and also Windows installation, visit the official website.