Sun says to turn monitors off overnight.

[Bob Sutterfield]

To settle a dispute, I just asked our local Sun hardware support person
whether we should turn our monitors off during expected long periods of
disuse, or simply leave them on with screen-savers running.  Speaking {\em
ex cathedra}, he said "I know it flies in the face of the conventional
wisdom of the ages throughout the industry, but the latest word from the
factory is to turn them off for periods as short as overnight - Sony,
Hitachi, Philips, all of them."

It surprised me too, but there you have it.