Abstract: A panel having an array of backlighted windows for displaying a change in a process variable from a nominal condition to a changed condition comprising a thin, sealed frame and a circuit board with an array of LEDs interconnected for each window and a binary switch coupled to the LED array that energizes the LEDs on receipt of a binary logic signal. The panel can be operated in a stand-alone unit or be backfitted to an existing data recorder, tapping into the incoming or internal logic variable signals and power supply without disturbing the underlying function of the recorder.