Reduce the health risk of the circadian- disrupting blue light from your PC and laptop at night.
A free program called f,lux works out when it is local sunset and quickly, or slowly, winds down the screen luminance and reduces the blue content of your screen. The next day the screen is back to normal. I have not yet tested the program but I suspect the program might also help in preserving ones night vision.
There are versions for Windows, Mac and Linux
http://www.sereopsis.com/flux/ typing in the address did not work for me,
But typing in 'f.lux' did.
Ken