Liquid crystal displays are used extensively in cellular telephones, pagers, watches, etc. Such displays are illuminated by light panels referred to as back lighting devices. Conventional devices generally utilize a light source mounted adjacent a plastic light waveguide for containing light from the light source entering the waveguide. Light is extracted from the waveguide by providing a surface that changes the reflective or transmissive characteristics of the waveguide causing light striking the surface to be transmitted out of the waveguide.
These conventional devices suffer from light loss associated with inefficient light coupling with the light source being placed next to the plastic waveguide. In conventional devices, the light source is often placed in a pocket in a clear plastic frame and a light waveguide or light sheet is positioned adjacent the light source in the frame. This pocket in the frame supports the light source. Electrical leads are electrically connected to the light source and are typically placed in a pocket adjoining the light source pocket, away from the light sheet. A reflective material, typically foil, is placed around the light source pocket and the area of the light sheet adjoining the light source pocket to reflect light into the light sheet. Foil is typically placed around the edges of the frame to reflect light striking it back into the light sheet.
In such a construction, the frame absorbs light, the light reflected is not efficiently useable and there is lack of a means to precisely position the light source. This results in a device that requires more power to provide a given level of illumination than is necessary.
In addition to these and other disadvantages associated with conventional back lighting devices, a differently sized back lighting device must be manufactured for a differently sized application.