The present invention relates to a lighting panel for lighting a display panel such as a liquid crystal display (LCD) from behind.
As a light source, an edge light is used for introducing light from an edge of the lighting panel. In order to provide a uniform light-beam, a plurality of edge lights must be used. However, if the light emitting diode (LED) is used as an edge light, the number of the LEDs causes increase of the cost.
FIG. 8 is a perspective view showing a conventional lighting panel of a display assembly, FIG. 9 is an enlarged side view thereof, FIG. 10 is a plan view, and FIG. 11 is a side view.
The display assembly comprises a lighting panel 101, three LEDs 102 as edge lights disposed at a front side 101c of the lighting panel, and an LCD 107 disposed above the lighting panel 101.
The lighting panel 101 is made of a transparent resin and has a light discharge side 101a and a light reflecting side 101b. There is formed a plurality of grooves 101d on the light reflecting side 101b. Each of the grooves 101d has a triangular sectional shape.
Light s2 emitted from the LEDs 102 enters the lighting panel 101 through the front side 101c. The light s in the lighting panel is reflected by the inside inclined surface of the groove 101d on the light reflecting side 101b and discharged from the light discharge side 101a. The discharged light 105 illuminates the underside of the LCD 107.
FIG. 12 is a plan view of the lighting panel 101 for showing distribution of light in the lighting panel, and FIG. 13 is an enlarged plan view of the lighting panel, FIG. 14 is a side view of the lighting panel, and FIG. 15 is an enlarged side view of the lighting panel.
As shown in FIGS. 12, 14 and 15, light rays s are widely distributed in the lighting panel 101. However, since an inclination angle El between the outermost light ray s1 and the front side 101c is comparatively large which is about 60°, there is formed large ineffective areas R and R1, from which light rays are not discharged from the lighting panel. As a result, the LCD 107 is not uniformly illuminated.