Solved! Lenovo support

Solution
It should turn off automatically. But if it isn't, go to the graphics options (i.e. right click on the desktop, etc...) and then you should be able to disable the laptop screen. Just be sure to re-enable it before you disconnect the vga.
It should turn off automatically. But if it isn't, go to the graphics options (i.e. right click on the desktop, etc...) and then you should be able to disable the laptop screen. Just be sure to re-enable it before you disconnect the vga.
 
Solution