Is there an option to switch off the monitor after a period of idleness. I can see the option to blank the screen with a black colour, but this is not the same, is it?

If you are using KDE:

Go to kcontrol, under the section Peripherals -> Display. Tab page Power Control. There you have three sliders and a check box.

Mark the check box labeled "Enable display power management", then choose your desires regarding the three timeouts. Press OK and you're done.

If you want to turn off your monitor without waiting, you can bind a keyboard shortcut to execute

Try it on a konsole. If it does not work then it usually means that your graphics card driver doesn't support it, or that it is not turned on in your Xorg.conf file.

Thank you.

You are welcome