Condensation control system for heated insulating glass units

A refrigerated cabinet door adapted to be mounted on a refrigerated cabinet, said door comprising:

• a first sheet of glass adapted to be positioned adjacent the ambient environment of the refrigerated cabinet and a second sheet of glass adapted to be positioned adjacent the interior of the refrigerated cabinet, each sheet of glass having an unexposed surface and an outer surface;
• a conductive coating applied to the unexposed surface of said first sheet of glass, said conductive coating having a hemispheric emissivity of less than 0.50;
• a frame secured around a periphery of said first and second sheets of glass for maintaining the glass sheets in parallel, spaced-apart relationship with the unexposed surfaces facing each other and creating a space therebetween;
• a pair of bus bars mounted along opposite edges on the unexposed surface of said first sheet of glass and electrically connected to said conductive coating, said bus bars each including a connector for connecting said bus bar to a power supply to form a circuit through said conductive coating;
• at least one optical sensor, mounted on the unexposed surface of said first sheet of glass and positioned in the space between said first and second sheets of glass, for directly sensing the presence of moisture on the outer surface of said first sheet of glass and generating a control signal in response thereto;
• and
• a control circuit electrically connected to said bus bars and said optical sensor for selectively transmitting current through said conductive coating in response to the control signal from said optical sensor.