an electromagnetic field created by the electrodes when power e g ac rf or pulsed power is applied however it is straightforward to arrange the electrodes so that only the outermost ring 20 or the innermost pixel 22 or the middle ring 24 or combinations thereof are excited in this manner the rings 20 24 may be separately controlled this effect can be used to alter the focal length in other embodiments more rings may be used and individually controlled by for example two or more sets of electrodes fig3 shows an actual image photographed with a telescope and a ccd camera of a prototype array in accordance with the invention the example array is composed of 100 u03bcm dia microdischarge pixels the visible light is produced by an ac discharge in neon gas in each microcavity and pairs of excitation electrodes can be seen in each of the microdischarges in fig3 the color appears slightly more yellow than is actually observed referring again to fig2 the array 10 is shown as being formed upon the substrate 14 which as another example might be a silicon wafer the substrate also for example might be selected from the group iii v semiconductor materials in still other embodiments the substrate may be plastic glass or another solid material onto which the remaining structure may be formed for the array 10 of fig2 formed on the silicon wafer or other semiconductor substrate an insulating layer 28 e g silicon dioxide provides electrical isolation from the electrodes 16 18 which may be connected through the insulating layer.