Plain light source device

Abstract: In a plain light source device used for backlighting a light transmission type liquid crystal display, a reflector (11) for reflecting the light from the light source (10) toward the liquid crystal panel (20) is provided which is formed from a conductive resin (plastic) consisting of a resinous (plastic) material with a metal fiber (14) mixed therein. The thus formed reflector (11) is an insulator at its surfaces and a conductor inside. A board (12) on which the light source (10) is supported is electrically and mechanically connected to the reflector (11) for grounding. The reflector (11) thereby serves as a shield against the noise generated by the light source (10). Further, a transparent conductive sheet (16) is disposed on the front side (on the display panel (20) side) of the light source (10), the conductive sheet (16) being electrically connected to the board (12) for grounding. As a result, the light source (10) is surrounded by the reflector (11) and the transparent conductive sheet (16), both grounded, thus providing further reliable shielding.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plain light source device, and more particularly to a plain light source device having a commonly used fluorescent tube as a light source for a backlighting of a light transmission type liquid crystal display device. 2. Description of the Prior Art When a fluorescent tube is used as a light source in a plain light source device for a backlighting of a light transmission type liquid crystal display device, there arises the problem that the fluorescent tube generates noise because of the application of a high voltage, which adversely affects the liquid crystal display device. To avoid this problem, there have heretofore been taken such measures as providing a reflector formed from a metal or a metal evaporated resin (plastic) as shown in Fig.1. In Fig,1, the numeral 1 indicates a resinous (plastic) reflector, and 2 a metal evaporated layer. Also, to prevent the noise interference to the display panel (liquid crystal panel), there have been taken such measures as disposing a mesh-like metal plate 3 shown in Fig.2 above the fluorescent tube or providing a transparent conductive sheet on the rear side of the panel. Generally, light transmission type liquid crystal display devices require a high-luminance uniform backlight, that is, a plain light source device. However, when the reflector formed from a metal or a metal evaporated plastic, as shown in Fig.1, is used, the luminance distribution on the display screen greatly varies depending on the shape of the reflector. This makes it extremely difficult to design a proper reflector, and a separate device such as a light curtain to be disposed above the fluorescent tube is required for uniform luminance distribution. Also, when the mesh-like metal plate 3 is provided above the fluorescent tube, as shown in Fig.2, to prevent the noise interference to the liquid crystal panel, the light emitted from the fluorescent tube is blocked by the metal plate 3. This reduces the efficiency of light utilization and therefore requires an increase in the output of the fluorescent tube to obtain high luminance, which results in a decrease in the efficiency of the lighting circuit. Furthermore, when the transparent conductive sheet is mounted on the rear side of the display panel, a complicated grounding method is required. SUMMARY OF THE INVENTION: In view of the above-enumerated problems, it is an object of the invention to provide a plain light source device which eliminates the need for external provision of noise preventive measures and which facilitates the designing of apparatus. According to the invention, there is provided a plain light source device comprising a light source disposed on the rear side of a display panel and a reflector for reflecting the light from the light source toward the display panel, wherein the reflector is formed of a conductive resin to reduce external interference due to electromagnetic radiation generated by the light source. The plain light source device of the invention preferably includes a board for holding the light source wherein the reflector is electrically connected to the board for grounding. The reflector is preferably formed in such a shape as to enclose the light source and has an open top facing the display panel. The reflector preferably has a white reflecting surface. Further, the plain light source device of the invention preferably includes a transparent conductive sheet disposed on the display panel side of the light source. Furthermore, the transparent conductive sheet is preferably electrically connected to the board for grounding. Moreover, the transparent conductive sheet is preferably formed from a transparent film with a thin metal film of ITO and so on evaporated on the surface thereof. According to the invention, the reflector, which is formed from a conductive resin, serves as a shield against the electromagnetic radiation (noise) by the light source. Also, since the reflector is a resinous molding, when the reflector has a white reflecting surface, the luminance distribution on the display screen is prevented from greatly varying depending on the shape of the reflector, which makes it possible to readily obtain uniformity in the luminance. Also, with a conductive sheet disposed on the display panel side of the light source, connection to the ground is facilitated, and also the light source is surrounded by the reflector and the transparent conductive sheet, thus achieving effective utilization of the light while providing further reliable shielding. As is apparent from the above description, according to the invention, the reflector is formed from a resin having conduction and therefore serves as a shield against the electromagnetic radiation (noise) generated by the light source. Also, since the reflector is a resinous molding, when the reflector has a white reflecting surface, the luminance distribution on the display screen is prevented from greatly varying depending on the shape of the reflector, which makes it possible to readily obtain uniformity in the luminance. Also, when a conductive sheet is disposed on the display panel side of the conductive sheet, connection to the ground is facilitated, and also the light source is surrounded by the reflector and the transparent conductive sheet, thus achieving effective utilization of the light while providing further reliable shielding. Accordingly, the invention has such excellent advantages as facilitating the designing of the reflector while providing shielding of the light source. BRIEF DESCRIPTION OF THE DRAWINGS: Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein: Fig.1 is a side view of a reflector 1 for plain light source device in a prior art; Fig.2 is a plan view of a metal plate 3 mounted above a light source to prevent noise interference to the display panel in the prior art plain light source device; Fig.3 is a side view of a plain light source device in a first embodiment of the invention; Fig.4 is a plan view of the plain light source device of Fig.3; Fig.5 is a cross sectional view of an essential portion of a reflector 11. Fig.6 is a cross sectional view of a plain light source device in a second embodiment of the invention; Fig.7 is a plan view of the plain light source device of Fig.6; and Fig.8 is a cross sectional view of a transparent conductive sheet 16. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawing, preferred embodiments of the invention are described below. [First Embodiment] A first embodiment is described below with reference to Figs.3 and 4. Fig.3 is a side view of a plain light source device according to the first embodiment of the invention. Fig.4 is a plan view of the plain light source device. As shown, the plain light source device of this embodiment, which is used for a backlighting of a light transmission type liquid crystal display device, comprises a light source 10 disposed on the rear side of a display panel (liquid crystal panel) 20 and a reflector 11 for reflecting the light from the light source 10 toward the display panel 20. The light source 10 consists of two fluorescent tubes (or U-shaped fluorescent tube) disposed parallel with each other inside the reflector 11, as shown in Figs.3 and 4. The light source 10 is supported on a light source supporting board 12. The reflector 11 is formed in a box-like shape from a resin having conduction, which consists of a resinous (plastic) material 13 with a metal fiber 14 mixed therein as shown in Fig.5, so that the reflector 11 has a shielding effect to prevent the noise generated by the light source 10 from causing external interference. The molding conditions are controlled so that the reflector 11 is an insulator at its surfaces and a conductor inside. Also, the reflector 11 is both electrically and physically (mechanically) connected to the light source supporting board 12 by means of a metal screw 15. The reflector 11 does not necessarily have to be formed in a box-like shape, but may be formed in other shape as long as it surrounds the light source 10 and has an open top facing the display panel 20. In the above construction, a conductive resin is used to form the reflector 11, to which the board 12 holding the light source 10 (fluorescent tubes) is screwed to provide grounding. The reflector 11 thus serves as a shield against the noise generated by the light source 10. Also, since the reflector 11 is a resinous molding, when the reflector 11 has a white reflecting surface, the luminance distribution on the display screen is prevented from varying greatly depending on the shape of the reflector 11, which makes it possible to readily obtain uniformity in the luminance. As a result, the designing of the reflector 11 is facilitated and shielding of the light source 10 can be provided. [Second Embodiment] Next, a second embodiment is described with reference to Figs.6 and 7. Fig.6 is a cross sectional view of a plain light source device in the second embodiment of the invention. Fig.7 is a plan view of the same. In Fig.7, the light source 10 is not shown for the sake of simplicity. As shown, the plain light source device of this embodiment includes a conductive sheet 16 disposed on the display panel 20 side of the light source 10 in order to achieve further effective shielding. As shown in Fig.8, the conductive sheet 16 is formed from a transparent film 18 with a thin metal film (ITO; Indium Tin Oxide) 19 evaporated thereon. As shown in Fig.7, a conductive metal tape 17 is attached to the conductive sheet 16, the conductive metal tape 17 being soldered to the light source supporting board 12 for electrical connection. Otherwise, the construction of this embodiment is the same as that of the first embodiment. In the above construction, the transparent conductive sheet 16 is disposed above (on the display panel 20 side of) the light source (fluorescent tubes) 10, with the conductive metal tape 17 attached thereto and soldered to the light source supporting board 12 for grounding. As described, since the conductive sheet 16 is disposed above the light source 10, connection to the ground is facilitated, and also the light source 10 is surrounded by the reflector 11 and the transparent conductive sheet 16, thus achieving effective utilization of the light while providing further reliable shielding. It will be appreciated that the invention is not limited to the above embodiments and that other modifications and changes can be made to the above embodiments within the scope of the invention. The invention may be embodied in other specific forms. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description.

Claims: A plain light source device comprising a light source (10) disposed on the rear side of a display panel (20) and a reflector (11) for reflecting the light from the light source (10) toward the display panel (20), wherein; the reflector (11) is formed of a conductive resin to reduce external interference due to electromagnetic radiation generated by the light source. A plain light source device as set forth in Claim 1, further comprising a board (12) for holding the light source (10), wherein the reflector (11) is electrically connected to the board (12) for grounding. A plain light source device as set forth in Claim 1 or 2, wherein the reflector (11) is formed surrounding the light source (10) and having an open top facing the display panel (20). A plain light source device as set forth in Claim 1, 2 or 3, wherein the reflector (11) has a white reflecting surface. A plain light source device as set forth in Claim 1, 2, 3 or 4, wherein a transparent conductive sheet (16) is disposed on the display panel (20) side of the light source (10). A plain light source device as set forth in Claim 5, wherein the transparent conductive sheet (16) is electrically connected to the board (12) for grounding. A light source according to any one of the preceding claims wherein said reflector (11) includes conductive particles (14) (e.g. metal fibres) distributed within the thickness of the resin.

Inventors: OYAMA HISASHI, TAKAHASHI NOBUYUKI, OYAMA, HISASHI, TAKAHASHI, NOBUYUKI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1991
Main classification: F21V7
IPC codes: F21V7, G02F1