JP4464412B2 - Planar light source device and liquid crystal display device using the same - Google Patents

Description

  The present invention relates to a planar light source device and a liquid crystal display device using the same.

  In the liquid crystal display device, a liquid crystal panel composed of two substrates sandwiched between liquid crystal layers and a planar light source device are provided on the back side of the liquid crystal panel. As a light source of a planar light source device, a linear cold cathode tube has been conventionally used as the light source. However, R, G, and B three-color light emitting diodes (hereinafter referred to as LEDs) are used because of their long life and good light emission. Some use a light source in which a plurality of each is arranged.

  The configuration of a conventional liquid crystal display device using this LED will be described with reference to FIG. 6A is a cross-sectional view, and FIG. 6B is a plan view. Reference numeral 1 denotes an LED, 2 denotes a reflector, 3 denotes a light guide plate, 8 denotes an optical sheet, 9 denotes a liquid crystal panel, and 10 denotes a reflecting sheet. A plurality of R, G, and B LEDs 1 are arranged to emit white light. The light emitted from the LEDs 1 of the respective colors is reflected directly or by the reflector 2 and enters the side surface of the light guide plate 3. The light incident on the light guide plate 3 propagates while repeating total reflection in the light guide plate. The light in the light guide plate is emitted to the entire surface (the entire light emitting surface) on which the optical sheet 8 is provided. The light emitted to the side opposite to the light emitting surface is reflected by the reflection sheet 10 and enters the light guide plate 3 again.

  The light emitted from the light emitting surface side of the light guide plate 3 passes through the optical sheet 8 composed of a diffusion sheet, a protective sheet, a lens sheet, a prism sheet, etc., and enters the liquid crystal panel 9. The liquid crystal panel 9 includes a CF substrate and a TFT array substrate that sandwich the liquid crystal layer. The CF substrate includes R, G, and B colored layers, a light shielding layer (BM), and the like, and the TFT array substrate includes switching elements and pixel electrodes. The liquid crystal layer is aligned by turning on and off the voltage by the switching element. Accordingly, the light reaching the liquid crystal panel 9 is modulated in accordance with the video signal, and displays each color of R, G, and B.

Since the planar light source device used in such a liquid crystal display device uses LEDs of different R, G, and B, changes in brightness and chromaticity occur in each color depending on the environment and temperature used. There is a problem that display characteristics deteriorate. Further, not only LEDs but also light sources using cold cathode fluorescent lamps have a problem that the luminance and light quantity of the entire light source change over time. Therefore, in Patent Document 1, a sensor is provided on the reflection sheet on the back side of the light guide plate. The light quantity of the light source is adjusted according to the value detected by the sensor.
Japanese Patent Laid-Open No. 10-222129

  However, when the sensor is provided on the reflection sheet on the back side of the light guide plate as in Patent Document 1, since most of the light is reflected by the reflection plate, the amount of light incident on the sensor is reduced. That is, stable detection could not be performed, and accurate control could not be performed.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a planar light source device and a liquid crystal display device that can suppress changes in luminance and chromaticity over time. .

The planar light source device according to the present invention includes a light source (for example, the LED 1 in the embodiment of the present invention) and a light guide plate that guides light from the light source to the entire surface (for example, the light guide plate 3 in the embodiment of the present invention). A sensor (for example, sensor 4 in an embodiment of the present invention) that is provided on a surface other than the light incident surface of the light guide plate and detects light from the light source, and is provided between the light guide plate and the sensor. And a refractive index adjusting member (for example, the refractive index adjusting member 6 in an embodiment of the present invention) having a refractive index smaller than the refractive index of the light guide plate, and the light source according to the value detected by the sensor The amount of light is adjusted. Thereby, the temporal change of the luminance and chromaticity of the planar light source device can be suppressed.

In addition , the amount of light incident on the sensor can be increased.

  In the above-described planar light source device, the sensor may be provided in the vicinity of a surface of the light guide plate that faces the surface on which the light source is provided. Thereby, stable light detection can be performed.

  In addition, another planar light source device according to the present invention includes a light source (for example, LED 1 in the embodiment of the present invention) and a light guide plate (for example, in the embodiment of the present invention) that guides light from the light source to the entire surface. A light guide plate 3) and a sensor (for example, sensor 4 in the embodiment of the present invention) provided on an inclined surface provided on at least a part of a surface opposite to the surface provided with the light source. ), And the light quantity of the light source is adjusted according to the value detected by the sensor. Thereby, the temporal change of the luminance and chromaticity of the planar light source device can be suppressed.

  Furthermore, another planar light source device according to the present invention includes a light source (for example, LED 1 in the embodiment of the present invention) and a light guide plate (for example, in the embodiment of the present invention) that guides light from the light source to the entire surface. A light guide plate 3) and a surface of the light guide plate facing the surface on which the light source is provided, or an inclined surface provided on at least a part of the surface facing the surface on which the light source is provided; A planar light source device that adjusts the amount of light of the light source according to the value detected by the sensor (for example, the sensor 4 in the embodiment of the present invention). At least a part or all of the surface of the light guide plate is roughened (for example, the rough surface portion 5 in the embodiment of the present invention), or a refractive index adjusting member (for example, between the light guide plate and the sensor). It is intended to provide a refractive index adjusting member 6) in the embodiment of the present invention. Thereby, the temporal change of the luminance and chromaticity of the planar light source device can be suppressed.

  In the above-described planar light source device, the light amount of the light source may be feedback controlled so that the light amount detected by the sensor is constant. As a result, changes in luminance and chromaticity over time can be suppressed, and color unevenness can be suppressed.

  As a preferred embodiment of the above-described planar light source device, a planar light source device using either a light emitting diode or a cold cathode tube as the light source can be mentioned.

  Red, blue, and green light emitting diodes are used as the light source. In the above-described planar light source device, the sensor detects a stimulus value of the emitted light, and the red, blue, and green colors are detected based on the detected stimulus value. The amount of light from each light emitting diode may be adjusted. As a result, changes in luminance and chromaticity of each color of the planar light source device over time can be suppressed.

  The above-described planar light source device is desirably used for a liquid crystal display device. Thereby, a liquid crystal display device in which changes with time in luminance and chromaticity are suppressed can be obtained.

  According to the present invention, it is possible to provide a planar light source device and a liquid crystal display device in which changes with time in luminance and chromaticity are suppressed.

Embodiment 1 of the Invention
A configuration of a liquid crystal display device using the planar light source device according to the present invention will be described with reference to FIG. FIG. 1A is a cross-sectional view of a liquid crystal display device according to the present invention, and FIG. 1B is a plan view thereof. Reference numeral 1 denotes an LED, 2 denotes a reflector, 3 denotes a light guide plate, 4 denotes a sensor, 5 denotes a rough surface portion, 7 denotes a feedback circuit, 8 denotes an optical sheet, and 9 denotes a liquid crystal panel.

  A plurality of R, G, and B LEDs 1 are arranged to emit white light. The light emitted from the LEDs 1 of each color is reflected directly or by the reflector 2 and enters the side surface of the light guide plate 3. The light incident on the light guide plate 3 propagates while repeating total reflection in the light guide plate 3. The light in the light guide plate is emitted to the entire surface (the entire light emitting surface) on which the optical sheet 8 is provided. The light emitted to the side opposite to the light emitting surface is reflected by the reflection sheet 10 and enters the light guide plate 3 again.

  The light emitted from the light emitting surface side of the light guide plate 3 passes through the optical sheet 8 composed of a diffusion sheet, a protective sheet, a lens sheet, a prism sheet, etc., and enters the liquid crystal panel 9. The liquid crystal panel 9 includes a CF substrate and a TFT array substrate that sandwich the liquid crystal layer. The CF substrate includes R, G, and B colored layers, a light shielding layer (BM), and the like, and the TFT array substrate includes a switching element and a pixel electrode. The liquid crystal layer is aligned by turning on and off the voltage by the switching element. Accordingly, the light reaching the liquid crystal panel 9 is modulated in accordance with the video signal, and displays each color of R, G, and B.

  Here, a sensor 4 for detecting light is provided in the vicinity of the center opposite to the light emitting surface of the light guide plate 3. The sensor 4 detects light from the light guide plate 3. The feedback circuit 7 adjusts the voltage or current supplied to the LED 1 based on the value output according to the detected light quantity. For example, when the amount of light is weak, the voltage or current supplied to the LED 1 is increased, and the amount of light of the LED 1 is increased. On the contrary, when the light quantity is strong, the voltage or current supplied to the LED 1 is lowered, and the light quantity of the LED 1 is lowered. This feedback is performed at appropriate time intervals, and the detected light quantity is adjusted to be constant. Thereby, the change of the brightness | luminance with time of the light emitted from LED1 can be suppressed. Here, a photodiode is a preferred example of the sensor 4. Thereby, even a small amount of light can be detected. Moreover, since the size is small, it can contribute to narrowing and thinning of the planar light source device and the liquid crystal display device.

  Also, if the amount of light incident on the sensor 4 is small, light cannot be detected stably, and accurate feedback may not be performed. In this case, the surface of the portion of the light guide plate 3 provided with the sensor 4 may be roughened. In this embodiment, the rough surface portion 5 is provided on the entire surface on which the sensor 4 is provided. Here, the surface on which the above-described sensor 4 is provided refers to a portion on which the sensor 4 is provided, not the entire surface of the light guide plate. In this case, the surface of the light guide plate 3 is roughened by subjecting the surface thereof to graining, sandblasting, satin finishing, or the like. Normally, light is not emitted from the back surface of the light guide plate 3 after total reflection, but the light is not emitted from the roughened portion, but the reflection angle of the light is changed and light is emitted from the portion. Therefore, the amount of light incident on the sensor 4 can be increased, and even when the amount of light is small, light can be detected stably and feedback can be accurately performed. Thereby, a planar light source device in which changes in light luminance and chromaticity are suppressed can be obtained.

  Furthermore, it is desirable to provide the sensor 4 with three types of sensors 4 for detecting tristimulus values X, Y, and Z, and to perform feedback control for each color. Thereby, the change of the brightness | luminance and chromaticity with time with respect to LED4 of each color can be suppressed, and it becomes possible to suppress a color nonuniformity. Therefore, it is possible to obtain a planar light source device in which changes in display characteristics for each color are suppressed. This planar light source device is preferably used for a liquid crystal display device.

Embodiment 2 of the Invention
The structure of the planar light source device according to the second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of the planar light source device, and only the portions necessary for explanation are shown. Since the same reference numerals as those in FIG. 1 indicate the same configuration, the description thereof is omitted. The configuration other than the illustrated configuration is the same as that in FIG. 1, and the feedback circuit 7 and the like are not illustrated.

  In the present embodiment, the sensor 4 is provided in the vicinity of the side surface opposite to the side surface on which the LED 1 is provided. By providing the sensor 4 at a location away from the LED 1, the tristimulus values X, Y, and Z are equalized, and more accurate detection can be performed. Similarly to the first embodiment, three types of sensors for detecting light of R, G, and B colors may be provided to perform feedback. Thereby, the change of the brightness | luminance and chromaticity with time with respect to LED4 of each color can be suppressed, and it becomes possible to suppress a color nonuniformity. Therefore, it is possible to obtain a planar light source device in which changes in display characteristics for each color are suppressed. This planar light source device is preferably used for a liquid crystal display device.

  In this embodiment, as shown in FIG. 2, a rough surface portion 5 is provided on the opposite surface of the light guide plate 3 where the sensor 4 is provided. In this case, the surface of the light guide plate is roughened, sandblasted, satin-finished, dot-printed, or the like, or the surface is roughened to have a prism shape or the like. Thereby, the reflection angle of the light reflected by the rough surface portion changes, and the light is emitted from the light guide plate 3 on the surface where the sensor 4 is provided. Thereby, even when the amount of light incident on the sensor 4 is small, the amount of light can be increased. Therefore, light can be detected stably and accurate feedback can be performed. Thereby, a planar light source device in which changes in light luminance and chromaticity are suppressed can be obtained.

Embodiment 3 of the Invention
The structure of the planar light source device according to the third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of the surface light source device, and only the portions necessary for the description are shown. The same reference numerals as those in FIG. 1 and FIG. The configuration other than the illustrated configuration is the same as that in FIG. 1, and the feedback circuit 7, the optical sheet 8, and the like are not illustrated.

  The present embodiment is different from the first and second embodiments in that a rough surface portion is not provided on the surface on which the sensor 4 is provided, and a refractive index adjusting member 6 is provided instead. The refractive index adjusting member 6 has a refractive index smaller than that of the light guide plate 3 and larger than that of atmospheric gas. For example, when the material of the light guide plate 3 is acrylic, its refractive index is about 1.49, so that a material having a refractive index that is an appropriate value smaller than 1.00 to 1.49 is selected as the refractive index adjusting member. As a result, the reflection angle of the light in the light guide plate changes at the boundary surface between the refractive index adjusting member 6 and the light guide plate 3, and the light is not totally reflected. Accordingly, the amount of light incident on the sensor 4 can be increased. Thereby, even when the amount of light incident on the sensor 4 is small, the amount of light can be increased. Therefore, light can be detected stably and accurate feedback can be performed. Thereby, a planar light source device in which changes in light luminance and chromaticity are suppressed can be obtained. In FIG. 3, the refractive index adjusting member 6 is illustrated in the same size as the sensor 4, but is not limited to the same size. For example, the refractive index adjusting member 6 may be larger than the sensor 4, and conversely, the refractive index adjusting member 6 may be provided only in a part of the sensor 4.

Embodiment 4 of the Invention
The structure of the planar light source device according to the fourth embodiment of the present invention will be described with reference to FIG. 4A is a cross-sectional view of the planar light source device, and FIG. 4B is a plan view, and only the portions necessary for the description are shown. The same reference numerals as those in FIG. 1 and FIG. The configuration other than the illustrated configuration is the same as that in FIG. 1, and the feedback circuit 7, the optical sheet 8, and the like are not illustrated.

  In this embodiment, as shown in FIG. 4, the sensor 4 is provided to be inclined with respect to the light guide plate 3, and the angle of the end face of the light guide plate in that portion is also changed. Thereby, in this part, the light in a light-guide plate is not totally reflected, but the light quantity of the light radiate | emitted from the end surface from which the angle is changing increases. Accordingly, the amount of light incident on the sensor 4 can be increased. Thereby, even when the amount of light incident on the sensor 4 is small, the amount of light can be increased. Therefore, light detection can be performed stably, and accurate feedback can be performed. Thereby, a planar light source device in which changes in light luminance and chromaticity are suppressed can be obtained. In addition, by making the portion where the sensor 4 is provided outside the display area, uniform display can be achieved over the entire display area. In the present embodiment, when the amount of light incident on the sensor 4 is small, a rough surface portion or a refractive index adjusting member may be provided as in the first, second, and third embodiments.

Embodiment 5 of the Invention
The configuration of the planar light source device according to Embodiment 5 of the present invention will be described with reference to FIG. FIG. 5 is a cross-sectional view of the surface light source device, and only the portions necessary for the description are shown. The same reference numerals as those in FIG. 1 and FIG. The configuration other than the illustrated configuration is the same as that in FIG. 1, and the feedback circuit 7, the optical sheet 8, and the like are not illustrated.

In the present embodiment, the sensor 4 is provided on the side surface of the light guide plate 3 opposite to the surface on which the LED 1 is provided. Therefore, the light emitted from the side surface of the light guide plate can be detected. Further, since the side surface of the light guide plate emits more light than the back surface, the light can be detected stably and accurate feedback can be performed.
Furthermore, since the sensor 4 is provided on the side surface of the light guide plate in the present embodiment, the thickness of the planar light source device need not be increased. In the present embodiment, when the amount of light incident on the sensor 4 is small, a rough surface portion or a refractive index adjusting member may be provided as in the first, second, and third embodiments.
Other embodiments.

  The planar light source device according to the present invention is provided with a sensor for detecting light on a light guide plate and feeding back the detected value to increase or decrease the light quantity of the light source. Thereby, even if the light from the light source fluctuates, it is possible to suppress changes with time in luminance and chromaticity of the planar light source device. Here, the light source is not limited to the LED shown in the above embodiment, and may be a light source using a cold cathode tube or EL (electroluminescence), for example. In the above-described embodiment, the light source is illustrated only on one side surface of the light guide plate, but is not limited to one side surface. For example, it may be provided on two opposing surfaces of the light guide plate, or may be provided on the back side.

  The place where the sensor is provided is not limited to the place illustrated in the above embodiment, and may be a place where light from the light source can be detected. In this case, it is desirable to provide a sensor other than the light incident surface and the light emitting surface. Thereby, it can display uniformly on the whole surface, without blocking the light from a light source. For example, when the sensor is provided on the back surface of the light emitting surface, there is little influence on the light emitting surface side, so that uniform display can be performed. Further, since the frame area is not expanded, there is no influence on the narrowing of the frame. Further, even when the sensor is provided on the side surface of the light guide plate, since the influence on the light emitting surface side is small, uniform display can be performed. Furthermore, it is not necessary to increase the thickness of the planar light source device. Further, by separating the position of the sensor from the light source, the color mixture of R, G, B light advances and becomes uniform. As a result, more accurate detection can be performed and stable feedback can be performed. Furthermore, it is desirable to provide a sensor for detecting the stimulus value of the emitted light and feed back to each color for any planar light source device in the above-described embodiment. Thereby, it is possible to suppress changes in luminance and chromaticity over time with respect to the LEDs of the respective colors, and it is possible to suppress color unevenness. Therefore, it is possible to obtain a planar light source device in which changes in display characteristics for each color are suppressed.

  Further, when the amount of light incident on the sensor is small and cannot be detected stably, it is desirable to roughen the surface of the light guide plate or provide a refractive index adjusting member. Thereby, the reflection angle of the light totally reflected in the light guide plate can be changed, and the light can be emitted to the outside of the light guide plate. Therefore, the amount of light incident on the sensor can be increased. The rough surface processing place may be any place where the amount of light to the sensor can be increased, and is not limited to the above embodiment. For example, the rough surface processing place may be a part or all of the surface where the sensor is provided, or may be near or around the surface where the sensor is provided. Further, it may be a part or all of the surface opposite to the surface on which the sensor is provided, or its vicinity or periphery. Furthermore, when the amount of light incident on the sensor is small, the above-described embodiments may be combined or used. If the amount of light incident on the sensor is sufficient, the rough surface portion and the refractive index adjusting member need not be provided.

  The above-described planar light source device is preferably used for a liquid crystal display device. Further, even when used for a display device other than a liquid crystal display device, a display device with stable luminance and chromaticity can be obtained.

FIG. 1A is a cross-sectional view showing a configuration of a liquid crystal display device according to Embodiment 1 of the present invention. FIG. 1B is a plan view showing the configuration of the liquid crystal display device according to the first exemplary embodiment of the present invention. It is sectional drawing which shows the structure of the planar light source device concerning Embodiment 2 of this invention. It is sectional drawing which shows the structure of the planar light source device concerning Embodiment 3 of this invention. FIG. 4A is a cross-sectional view showing a configuration of a liquid crystal display device according to Embodiment 4 of the present invention. FIG. 4B is a plan view showing the configuration of the planar light source device according to Embodiment 4 of the present invention. It is sectional drawing which shows the structure of the planar light source device concerning Embodiment 5 of this invention. FIG. 6A is a cross-sectional view showing a configuration of a conventional liquid crystal display device. FIG. 6B is a plan view showing a configuration of a conventional liquid crystal display device.

Explanation of symbols

1 LED
2 Reflector 3 Light guide plate 4 Sensor 5 Rough surface portion 6 Refractive index adjusting member 7 Feedback circuit 8 Optical sheet 9 Liquid crystal panel 10 Reflective sheet

Claims (8)

A light source;
A light guide plate that guides light from the light source to the entire surface;
A sensor that is provided on a surface other than the light incident surface of the light guide plate and detects light from the light source;
A refractive index adjusting member provided between the light guide plate and the sensor and having a refractive index smaller than the refractive index of the light guide plate ;
A planar light source device that adjusts the light amount of the light source based on a value detected by the sensor. The planar light source device according to claim 1 , wherein the sensor is provided in a vicinity of a surface facing the surface on which the light source is provided of the light guide plate. A light source;
A light guide plate that guides light from the light source to the entire surface;
A sensor for detecting light from the light source, provided on an inclined surface provided on at least a part of a surface facing the surface provided with the light source;
A planar light source device that adjusts the light amount of the light source based on a value detected by the sensor. A light source;
A light guide plate that guides light from the light source to the entire surface;
A sensor for detecting light from the light source provided on a surface of the light guide plate facing the surface on which the light source is provided or an inclined surface provided on at least a part of the surface facing the surface on which the light source is provided; Prepared,
A planar light source device that adjusts the light amount of the light source according to a value detected by the sensor,
A planar light source device in which at least part or all of the surface of the light guide plate on which the sensor is provided is roughened, or a refractive index adjusting member is provided between the light guide plate and the sensor. Surface light source device according to any one of claims 1 to 4 light amount detected by the sensor is fed back controls the amount of the light source to be constant. Surface light source device according to any one of claims 1 to 5 is used either light emitting diode or a cold cathode tube light source. Red, blue and green light emitting diodes are used as the light source,
The sensor detects the stimulus value of the emitted light,
The planar light source device according to any one of claims 1 to 6 , wherein the amount of light from each of the red, blue, and green light emitting diodes is adjusted according to the detected stimulus value. The liquid crystal display device using the surface light source device according to any one of claims 1 to 7.

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