Disable Asus X53U Laptop screen using HDMI cable

I am using an Asus X53U Laptop.

I am using hdmi cable to watch on my t.v.., so I wish to disable the image
or darken the laptop screen without affecting the display on the t.v. screen,
since I don't need to have the laptop and t.v. screen on at the same time.

So how do I disable and enable the laptop screen using Windows 7 ?


Thanks