One aspect is a device for displaying an indication of a system parameter. The device includes an input circuit, an optical sense circuit, a control circuit, and an output circuit. The input circuit is configured to receive input signals that are indicative of a measured system parameter. The optical sense circuit is configured to receive sense signals indicative of a sensed level of light and to receive programming signals related to a system parameter. The control circuit is configured to correlate the input and programming signals and to produce control signals dependant thereon. The output circuit is configured to display an indication of a system parameter that is based upon the control signals.