Lighting devices which produce diffused light at relatively low intensity to provide sufficient visible light useful for human eyes to discern objects in the dark, are extensively used where low-level lighting is desirable. In particular, an electroluminescent cover plate is routinely used as a night-light over a conventional electrical receptacle, typically a duplex wall receptacle (using one of the two available plug-in portions or sockets) or over a receptacle which may include a light switch in a bathroom or bedroom (using the only available socket). A commercially available night-light, such as one sold under the trademark Limelites by Austin Innovations as Model No. 11100, may be plugged into the socket of a conventional wall receptacle. The popularity of the electroluminescent cover plate derives from its inherently "fail-safe" construction, and its ability to operate continuously for an arbitrarily long time, producing a subdued lighting.
In U.S. Pat. No. 3,588,489 to Gaines there is illustrated an electroluminescent panel between dual receptacles in a unique body case which houses three sets of opposed contact slots separated by a pair of vertically grooved transverse ribs. The panel is centered between openings for prongs to be plugged into the corresponding receptacle beneath the cover which is an application-specific cover plate for a wall-mounted duplex receptacle. The cover has a pair of opposed prongs which are inserted in opposed contact slots to provide current to the panel.
A few years later U.S. Pat. No. 3,307,030 to DeFrancisco disclosed an electroluminescent cover plate which provided plug apertures or a slot for a switch handle, but required that the plate have a pair of prongs which were to be plugged into a plug-in receptacle which required an extra central plug-in portion into which the prongs could be plugged into.
Very recently, in U.S. Pat. No. 5,485,356, Nguyen teaches a cover plate for a duplex receptacle, and to the rear surface of the plate is secured a resilient and flexible U-shaped conductive strip the arms of which provide contact plates which are inserted into contact members on each side of the body of the receptacle. The purpose of the device is to energize an indicator light when the receptacle is energized. The cover plate itself is not active and relies on the indicator light to indicate whether the receptacle is energized.