The display backlight will come on when there is an active alarm, trouble, or supervisory present. It will also be on when in programming, in test mode and if a key is pressed when the panel is in normal condition the backlight will come on.
Part numbers FPD-7024, D7024, DS9400, DS9400I, DS9400M, DS9447, DS9436, D7033, D7036, FMR-7033, FMR-7036