DPMS
The 1993 VESA standard that lets a graphics card tell the monitor it may go to sleep, and the X11 extension of the same name that drives it through xset.
Display Power Management Signaling grew out of the US EPA's Energy Star programme, which from 1992 expected office equipment to cut its draw when nobody was using it. The standard defines four states – on, standby, suspend and off – and signals them in the simplest way imaginable: by dropping the horizontal sync pulse, the vertical one, or both. A CRT that lost sync blanked its electron beam and cooled down to varying degrees; the deeper the sleep, the longer the warm-up when somebody nudged the mouse.
In X11 the standard survives as the DPMS extension, written at Digital Equipment in the mid-1990s and long since standard in X.Org. The timers are set with xset dpms 600 900 1200 and switched off altogether with xset -dpms, the first command every kiosk builder learns. It is separate from the screen saver: that one blackens the picture, DPMS turns the display off. On an LCD the three sleep states amount to the same thing, backlight off, but the kernel's DRM layer still carries all four values around, a greeting from the age of the picture tube.