HP Vectra XU5 Reference Manual page 62

Energy Saving Screen Blanking
If the display has power management capabilities, the video controller can reduce the
display's power consumption by blanking the screen. This can be enabled by selecting
power management options in the PC's SETUP program. When the PC enters a power-
saving mode, the video controller is instructed to cut the horizontal and vertical
synchronization signals to the monitor. This action blanks the screen and reduces the
display's power consumption.
Vectra XU Technical Reference The Integrated Ultra VGA Controller 62