This repair guide may help fix Nokia 1508 keypad light not glowing or not working problem.
To fix the keypad light you may first check the two keypad LED's then trace its connection line paths through the components where it is being connected.
The filter resistor is connected to negative supply voltage of the keypad LED light. check it also.
If the procedure above does not solved the problem. You may then try to rework or replace the LED driver IC. Hope this help and serve as Nokia 1508 Keypad light problem solution.