My personal laptop is an old Dell Latitude E6410. One of the things I actually love about it, is the fact that the keyboard has a backlight.
However, because Linux, sometimes that backlight just stops working. When this happens, you'll see error messages in dmesg, such as:
dell_wmi: Unknown key with type 0x0011 and code 0x01e2 pressed
If this happens to you, just run this command:
$ sudo echo 7 > /sys/devices/platform/dell-laptop/leds/dell\:\:kbd_backlight/brightness
You can echo a higher number if you want your keyboard brighter, but …