Samsung Galaxy S4’s capacitive keys are turned on when you use the phone and they automatically turn off when the phone is not being used.But you can also turn off their light even when you are using the phone and this can be easily done.
To turn off capacitive keys light, go to Settings > My Device Tab > Display and scroll all the way down to tbe bottom and select Touch key light. There you can choose how many seconds you want them to be on.
That’s it. If you have any questions please leave a comment below.