Apple - How can I force my keyboard backlight to turn on?
gentmatt’s answer seems useful!
Alternatively, you could try going to System Preferences → Keyboard, and unchecking the “Automatically illuminate keyboard in low light” setting. That should prevent the “disabled” icon from your screenshot altogether.
LabTick allows you to manually control the keyboard backlight:
You can just put your hand front of iSight sensor and then press backlight keys.
Like this:
