A transparent electroluminescent display panel overlaps at least a part of a conventional instrument panel, and forms a combined display panel assembly. Overlapping front and back panel displays are selectively displayed. The front electroluminescent panel displays additional information such as navigation maps, and is turned off when such additional information is not required while the back panel is turned on. The present invention eliminates undesirable reflected images of the back panel vaguely shown on the front panel when the front panel is on and the back panel is off. A light attenuator, eliminates the reflected images. It decreases the intensity of light emitted from the front panel to the back panel, and is disposed between the back and the front panels or built into the electroluminescent panel, so that the reflected images are eliminated.