Abstract: Apparatus for changing a dimension of the light-producing area in a display element of the type which emits light from any portion of an interface zone across which a voltage exceeding a certain threshold is established, by varying this voltage. A bias voltage source provides a potential along one side of the interface zone, which increases from one end to the other, with respect to the other side. The apparatus is particularly well suited for an electronic bar graph type indicator. Gas discharge devices such as plasma tubes, and LED's are particularly suitable types of display elements.