The keyboard backlight can be turned off and on via the key combination "Fn + Y" while you are in Windows.
There are three options to choose from:
1. Keyboard backlight on (timed lighting)
2. Keyboard backlight on
3. Keyboard backlight off
To change the option you are using, hold down the "Fn" key and repeatedly press the "Y" key to cycle through the options. Then, when you have chosen which backlight option you want, release both keys.