Reply to S4- Loop display not illuminating

Hey guys, got my s4 a few days ago and i love it!
i cant seem to figure out how to get the loop display (the little box above the loop knob that shows the amount of bars you set the loop for) to illuminate.
im pretty sure it works because it lights up when i turn the s4 on initially but then goes off and doesnt come back on.

could it be faulty or am i missing something here as i have searched everywhere but cant find any info.