Set keyboard brightness in Windows with Boot Camp on Mac
The keyboards on some portable Mac computers provide backlighting, so that the keys are visible in low light conditions. If keyboard backlighting is on, the keys light up automatically whenever the ambient light is low.
Automatically turn off keyboard backlighting when your computer is idle
In Windows, click
in the right side of the taskbar, click the Boot Camp icon 
, then choose Boot Camp Control Panel.If a User Account Control dialog appears, click Yes.
Click Keyboard.
Drag the “Turn off keyboard backlight when computer is not used for” slider.
Change keyboard backlighting
In Windows, press the F5 key to decrease keyboard backlighting, or press the F6 key to increase keyboard backlighting. You may need to hold down the Fn key as you press the F5 or F6 key.
If the F5 and F6 keys don’t adjust backlighting, make sure you have the latest Windows support software installed. In macOS, choose Apple menu > App Store, then install all available updates.