Originally Posted by nosidam
Turn off the auto dim and it will always light up.
I see the OP is on an 8330 but the above statement is a negative on my 4.5 8320. The keyboard lighting is extremely arbitrary. Doesn't seem to be any rhyme or reason to when it wants to light up.
I upgraded the OS less than two days after buying the device so I can't recall if it was like that before the upgrade or not.