I can't find "function key" for swiching off the screen immediately...
Don't mess this with going to sleeping or hibernation state. I just need to swich off the screen during some computer jobs (to save battery life) or hide the view from someone who comes to me
Such a key combination is not available to turn off the screen immediately.
But what you can do to save battery life is setting dimmed display brightness in Windows power options. There you can set the dimmed display brightness to 10% for example and dim display after2 or 3 minutes.