SCREEN BURN
by Editor, NYBUG, June 1987

(What happens when you leave your computer on)

Q.  Sometimes I leave my computer on for hours at a time.  Can
this practice harm the machine?

A.  The back of your monitor is coated with phosphors which glow
when bombarded with a stream of electrons.  This bombardment can
be controlled to create the precise images on your screen, but if
it is kept on for a long period of time, the phosphors of that
image will burn out, leaving a permanent "ghost" on your screen. 
There are programs that will turn off your blank after a few
minutes if a key is not pressed.  This will prevent the problem.