"Light at night is bad for your health, and exposure to blue light emitted by electronics and energy-efficient lightbulbs may be especially so."
Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in (relative) darkness. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.
But we may be paying a price for basking in all that light. At night, light throws the body’s biological clock—the circadian rhythm—out of whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.
But not all colors of light have the same effect. Blue wavelengths—which are beneficial during daylight hours because they boost attention, reaction times, and mood—seem to be the most disruptive at night. And the proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown." (http://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side)
Redshift is an application that adjusts the computer display's color temperature based upon the time of day. The program is free software, inspired by the proprietary f.lux, and is intended to reduce eye strain as well as insomnia.
To install redshift on Ubuntu , open a terminal (ctlr+alt+t) and type in the following command :
sudo apt install redshift redshift-gtk
After the installation is complete close the terminal and lanch redshift from Dash .
Redshift can be enabled to start on boot by clicking on "Autostart"