Separe e desconecte a luz de fundo. :)
Seu notebook provavelmente tem uma chave de alternância de monitor interno / externo, talvez alternando para 'externo' sem nenhum monitor externo conectado?
Ou talvez confira vbetool :
Use vbetool to turn off the backlight in an LCD display from the Linux command line. This is useful if using Linux on a laptop computer in text mode. The normal screen blanking utilities do not turn off the backlight, leaving a dull glow and using power unnecessarily. The vbetool utility can manipulate the VESA DPMS (Display Power Management Signaling) features of the display. DPMS can turn off the backlight. Use vbetool dpms off to turn it off, vbetool dpms on to turn it on.
This is not a screensaver, the display will not turn back on by using the keyboard, it has to be turned back on with vbetool or reboot the computer. Remotely accessing the computer with ssh can be used to turn the display on or blind typing on the console can be used. The vbetool command could be put in a startup script like rc.local to boot with the display off.
Acima da sinopse de aqui .