Set keyboard brightness in Windows with Boot Camp on Mac
In Windows on an Intel-based Mac, you can adjust the keyboard backlighting. The keyboards on some Mac laptop 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 adjust keyboard backlighting
In Windows on your Mac, 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.
Do any of the following:
Automatically turn off keyboard backlighting after a period of inactivity: Drag the “Turn off keyboard backlight when computer is not used for” slider to the desired setting.
Automatically change keyboard brightness in low light: Select the “Adjust keyboard brightness in low light” checkbox.
Manually adjust keyboard backlighting
In Windows on your Mac, do any of the following:
Adjust keyboard backlighting: Press the increase keyboard brightness key
or the decrease keyboard brightness key 
.Turn keyboard backlighting off: Press the decrease keyboard brightness key
until the keyboard is no longer lighted.Turn keyboard backlighting on: Press the increase keyboard brightness key
until the keyboard is bright enough for your needs.Use function keys to adjust keyboard backlighting: Press the F5 key to decrease keyboard backlighting, or press the F6 key to increase keyboard backlighting. You may need to press and hold the Fn key as you press the F5 or F6 key.
If the keys don’t adjust the backlighting, make sure you have the latest Windows support software installed. See the Apple Support article Download and install Windows support software on your Mac.