JP2004288480A - Planar light source device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light source device and a liquid crystal display device capable of obtaining stable brightness against fluctuation of environmental temperature or the like. <P>SOLUTION: Gas pressure of at least one discharge tube 1 out of two or more pieces of discharge tubes 1, 2 is made different from that of the other tubes 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flat light source device and a liquid crystal display device, and mainly relates to a flat light source configuration having a light source configuration for obtaining stable luminance against environmental temperature changes when used as a light source of a liquid crystal display device. The present invention relates to a light source device and a liquid crystal display device.
[0002]
[Prior art]
2. Description of the Related Art A liquid crystal display device has features such as small size, light weight, and low power consumption, and thus is widely used as a display monitor of an information device terminal, a television, a portable information device terminal, a video camera, and the like.
[0003]
Since a liquid crystal material is not a self-luminous element, some light source is required for use as a display device. In the case of a reflective liquid crystal display device, indoor lighting or the like is used as a light source or a front light is used as a light source.
[0004]
On the other hand, in the case of a transmissive liquid crystal display device, a backlight which is a flat light source is required on the back of the liquid crystal panel. This backlight is roughly classified into a sidelight type and a direct type (for example, see Patent Reference 1 and Patent Document 2).
[0005]
Among them, in the former sidelight method, light emitted from a linear light source is efficiently taken in from a light incident end face of a light guide plate and converted into a planar light source.
In the latter direct-lighting method, a plurality of linear light sources are arranged immediately below a flat light-emitting surface.
[0006]
Here, an example of a sidelight type backlight will be described with reference to FIG.
FIG. 9 is a cross-sectional view of a main part of a liquid crystal display panel module provided with a backlight of a sidelight type, which includes a liquid crystal display panel 31, a spacer 32 supporting the liquid crystal display panel, a linear light source 33, and a linear light source. , A light guide plate for guiding the emitted light into the plane, a reflector plate for reflecting the light from the light guide plate toward the display surface, and light toward the display surface side. And a shield case 38 for accommodating the whole, and a diffusion plate 37 for diffusing the light to obtain uniform in-plane luminance.
[0007]
A cold cathode tube is generally used as a linear light source of the backlight of each of these types, and mercury is sealed in the cold cathode tube.
Actually, a rare gas such as neon or argon is sealed in the cold cathode tube other than mercury in order to improve the lighting property (for example, see Patent Document 3).
[0008]
This mercury is partially vaporized and dispersed in the tube, but the efficiency of the cold cathode fluorescent lamp largely depends on the mercury vapor pressure inside the tube, and the mercury vapor pressure itself also changes with the ambient temperature outside the tube. And has a peak of luminous efficiency around an ambient temperature slightly exceeding 40 ° C.
[0009]
Some of the electrons that fly out of the electrodes at both ends of the cold cathode tube collide with mercury molecules and contribute to light emission. The electrons also collide with the rare gas molecules.
When the electrons collide, heat is generated and the temperature of the entire tube is increased.However, when the pressure of the rare gas is high, the number of molecules of the rare gas increases, so the calorific value increases, and therefore, the cold cathode tube The luminous efficiency of is determined not only by the pure mercury vapor pressure but also by the gas pressure of the rare gas.
[0010]
In such a liquid crystal display device, in general, a thermal design of the liquid crystal display device is performed in order to maximize the luminous efficiency of the cold cathode tube in an operation state in which the liquid crystal display device is thermally stable. Alternatively, the gas pressure of the cold cathode tube is adjusted.
[0011]
[Patent Document 1]
JP 2000-01977 [Patent Document 2]
JP 2000-162593 A [Patent Document 3]
JP 07-176292 A
[Problems to be solved by the invention]
However, when the ambient temperature is lower than the temperature at which the luminous efficiency of the cold-cathode tube is at an optimum state, the luminous efficiency is reduced and the luminance becomes low, and the display quality is lowered. Until the temperature is reached, there is a problem that the same low-brightness display quality is obtained.
[0013]
That is, since the cold-cathode tube has a characteristic that the temperature dependence on the luminous efficiency is large, the amount of change in the luminance of the liquid crystal display device becomes large in an environment where the temperature changes greatly.
For example, in the case of a liquid crystal display device having the highest luminous efficiency at an ambient temperature of 25 ° C., the brightness decreases at lower or higher temperatures, and the display quality deteriorates.
[0014]
Further, the liquid crystal display device is usually used in a state of being stood at about 90 ° with respect to a horizontal plane, but there is a problem that the brightness is different at the top and bottom of the screen and the display quality is deteriorated.
[0015]
For example, when a sidelight type backlight is used, cold-cathode tubes may be disposed on the upper and lower light-incident end faces of the light guide plate, respectively, as described above. Are provided with reflectors for the purpose of efficiently entering light into the light guide plate.
[0016]
In this case, heat generated from the cold cathode tube generates convection in the reflector.
That is, since the reflector is disposed above the cold-cathode tube above the light guide plate and the light guide plate below the cold-cathode tube, the heat generated from the cold-cathode tube rises due to the convection of air in the reflector and reaches the reflector. However, since the reflector is usually made of a metal material, most of the heat is radiated to the outside through the reflector.
[0017]
On the other hand, on the lower side of the light guide plate, the light guide plate is located above the cold-cathode tube and the reflector is located below the cold cathode tube, so that the heat is increased by the convection and absorbed by the light guide plate first. The heat is radiated to the outside.
[0018]
As described above, as a result of the heat radiation paths being different between the upper side and the lower side of the light guide plate, the lower side becomes higher by several degrees Celsius between the upper cold cathode fluorescent lamp and the lower cold cathode fluorescent lamp, and the brightness difference between the respective cold cathode fluorescent lamps is different. Is generated, which causes a problem that the luminance is different between the upper and lower portions of the screen.
[0019]
Therefore, an object of the present invention is to obtain a stable luminance against a temperature change such as an environmental temperature.
[0020]
[Means for Solving the Problems]
FIG. 1 is a diagram showing the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Reference numeral 4 in the figure denotes a reflector that condenses light from the discharge tubes 1 and 2 toward the light guide plate 3 and reflects the light.
See FIG. 1 In order to solve the above problem, the present invention relates to a flat light source device in which at least two or more discharge tubes 1 and 2 serving as a light source are arranged. Is different from the gas pressure of the discharge tube 2.
[0021]
As described above, by using a plurality of discharge tubes 1 and 2 having different gas pressures as light sources, a temperature-dependent luminance obtained by averaging the respective temperature characteristics can be obtained. And a stable display luminance can be obtained.
[0022]
In this case, it is desirable that the composition ratio of the main gas, that is, Ne + Ar, sealed in the two or more discharge tubes 1 and 2 is the same in all the discharge tubes 1 and 2. For example, Ne: Ar = 97. : Make it 3 mag.
The main gas is not limited to Ne and Ar, and another rare gas such as Kr may be used.
[0023]
Such a flat light source device is applied to a side light system using a light guide plate 3. In this case, a plurality of discharge tubes 1 and 2 are arranged at both ends of the light guide plate 3, respectively. The gas pressure of at least one of the plurality of discharge tubes 1 and 2 may be different from the gas pressure of the other discharge tubes 2 among the plurality of discharge tubes 1 and 2 arranged at each end. A display with no difference is obtained.
[0024]
When the light guide plate 3 is used upright with respect to a horizontal plane, the gas pressure of the discharge tubes 1 and 2 disposed at the upper end of the light guide plate 3 and the lower end of the light guide plate 3 are disposed. The gas pressures of the discharge tubes 1 and 2 may be different from each other, so that a decrease in display quality due to a vertical temperature difference caused by convection due to heat generation of the discharge tubes 1 and 2 can be reduced.
[0025]
Further, such a flat light source device is also applied to a direct type in which a plurality of discharge tubes 1 and 2 are disposed immediately below a light emitting plane. It is desirable that the pressure be different between the discharge tubes 1 and 2 adjacent to each other, whereby it is possible to obtain a stable and in-plane uniform brightness with respect to a temperature change.
[0026]
Further, it is desirable to connect the plurality of discharge tubes 1 and 2 to the discharge tube drive circuit by independent electrical connection means such as wiring, and to connect the discharge tubes 1 and 2 having different gas pressures to each other according to the respective gas pressures. By setting different tube currents or tube voltages, stable display luminance can be obtained with respect to temperature changes.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Here, a sidelight type backlight according to the first embodiment of the present invention will be described with reference to FIGS.
FIG. 2 is a schematic perspective view of a sidelight type backlight according to the first embodiment of the present invention, and here is a main part of the technical idea of the present invention in order to simplify the description. Although only the light source portion is shown, it is actually provided with a reflection plate, a diffusion plate and the like as shown in FIG.
[0028]
The backlight of the sidelight type has a low-gas-pressure cold-cathode tube 12 and a high-gas-pressure cold-cathode tube 13 at each end of the light incident on the long side of the light guide plate 11 in each of the reflectors 14 and 15. It is arranged in.
[0029]
In this case, the composition ratios of the main gas in the low-gas-pressure cold cathode tubes 12 and the high-gas-pressure cold-cathode tubes 13 are set to be the same.
For example, the ratio of the main gas Ne and Ar is set to Ne: Ar = 97: 3, and the same applies to other embodiments described below.
Note that the content of Hg is very small relative to the main gas.
[0030]
Although not shown, the low-gas-pressure cold-cathode tube 12 and the high-gas-pressure cold-cathode tube 13 are connected to a discharge tube driving circuit by different electrical connection means such as wiring. An optimal tube current is set to flow according to each gas pressure, and the same applies to other embodiments described below.
[0031]
By arranging cold-cathode tubes with different gas pressures as described above, it is possible to obtain a certain level of brightness over a wide temperature range, and when used as a backlight of a liquid crystal display device, the ambient temperature change may occur. , Stable display quality can be maintained.
[0032]
3 (a) and 3 (b) FIG. 3 (a) is an explanatory diagram of the temperature dependence of the luminous efficiency in the present invention, and FIG. 3 (b) is the temperature dependence of the luminous efficiency in the conventional backlight. FIG.
As shown in FIG. 3B, in a backlight using the same discharge tube, the temperature range in which light emission luminance of a certain level or more can be obtained is narrow, but in the backlight of the present invention, the sum of different temperature characteristics and Therefore, the temperature range in which light emission luminance of a certain degree or more can be obtained is widened.
[0033]
That is, the high gas pressure cold cathode tube 13 has a larger number of gas molecules than the low gas pressure cold cathode tube 12, so that the number of collisions of electrons increases. Even when the ambient temperature is lower than that of the tube 12, the desired mercury vapor pressure is reached, and the luminous efficiency is improved even when the design optimum temperature is relatively high.
[0034]
On the other hand, the cold-cathode tube 12 having a low gas pressure has a smaller number of gas molecules than the cold-cathode tube 13 having a high gas pressure, so that the number of electron collisions is reduced. Even when the ambient temperature is higher than that of the cathode tube 13, the desired mercury vapor pressure is reached, and the luminous efficiency is improved even when the design optimum temperature is relatively low.
[0035]
In addition, the initial lighting period is a low temperature state until a thermally stable state is reached, and the luminous efficiency is usually low. Can be reduced.
[0036]
Next, a sidelight type backlight according to a second embodiment of the present invention will be described with reference to FIG.
FIG. 4 is a schematic perspective view of a sidelight type backlight according to a second embodiment of the present invention. Here again, for simplicity of description, a main part of the technical idea of the present invention is shown. Although only the light source portion is shown, it is actually provided with a reflection plate, a diffusion plate and the like as shown in FIG.
[0037]
In the backlight of the sidelight type, a high-gas-pressure cold-cathode tube 13 is disposed in a reflector 14 at a light-entering end on one long side of a light guide plate 11, and the light is input to the other long side of the light guide plate 11. A low-gas-pressure cold-cathode tube 12 is disposed inside a reflector 15 at the light end.
[0038]
Even with such a configuration, since the light incident from both light incident ends is mixed in the light guide plate, the same characteristics as those of the first embodiment can be obtained. This is effective in a state where the display surface, which is a normal installation state of the display panel, is set at approximately 90 ° with respect to the horizontal plane.
[0039]
That is, as described above, as a result of the heat radiation paths being different above and below the light guide plate 11, the upper cold cathode tube and the lower cold cathode tube are higher by several degrees Celsius on the lower side, and the respective cold cathode tubes Although a brightness difference is produced, the upper cold cathode tube is a high gas pressure cold cathode tube 13 and the lower cold cathode tube is a low gas pressure cold cathode tube 12, so that there is no difference between the upper and lower brightness and good. Display quality can be obtained.
[0040]
This is because, by using the cold cathode tube on the lower side, which is the lower side, as the cold cathode tube 13 having a high gas pressure, a predetermined light emission luminance can be ensured even at a low temperature, and the lower cold cathode tube, which is the higher side, on the low gas side. This is because a predetermined emission luminance can be ensured even at a high temperature by using the cold cathode tube 12 described above.
[0041]
Next, a sidelight type backlight according to a third embodiment of the present invention will be described with reference to FIG.
FIG. 5 is a schematic perspective view of a sidelight type backlight according to a third embodiment of the present invention. Here again, the main part of the technical concept of the present invention will be described in order to simplify the description. Although only the light source portion is shown, it is actually provided with a reflection plate, a diffusion plate and the like as shown in FIG.
[0042]
This sidelight type backlight has the same basic configuration as that of the first embodiment, but is applied here to a backlight for a screen having a vertically long display surface of a liquid crystal display panel. When the lamp is set up as in a normal use mode, the cold cathode tubes 12 and 13 constituting the backlight are arranged at the left and right ends of the light guide plate 11.
[0043]
Next, a sidelight type backlight according to a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 6 is a schematic perspective view of a backlight of a sidelight type according to a fourth embodiment of the present invention. Here again, for simplification of description, a main part of the technical idea of the present invention is shown. Although only the light source portion is shown, it is actually provided with a reflection plate, a diffusion plate and the like as shown in FIG.
[0044]
This sidelight type backlight has the same basic configuration as that of the first embodiment, but here, only one end of the light guide plate 11 is connected to the cold cathode tube 12 of low gas pressure and the high A gas pressure cold cathode tube 13 is provided inside a reflector 14.
[0045]
Next, a direct-type backlight according to a fifth embodiment of the present invention will be described with reference to FIG.
FIG. 7 is a schematic perspective view of a direct-type backlight according to a fifth embodiment of the present invention. Here again, a light source which is a main part of the technical idea of the present invention for simplifying the description. Although only the portion is illustrated, a diffusing plate or the like is actually provided.
[0046]
In the fifth embodiment, low-gas-pressure cold-cathode tubes 12 and high-gas-pressure cold-cathode tubes 13 are alternately arranged inside a housing serving as a reflection plate 16.
[0047]
In this case, since the cold-cathode tubes 12 having a low gas pressure and the cold-cathode tubes 13 having a high gas pressure are alternately arranged, a stable luminance can be obtained with respect to a temperature change, and good in-plane uniformity can be obtained. can get.
[0048]
Next, a front light of a sidelight type according to a sixth embodiment of the present invention will be described with reference to FIG.
FIG. 8 is a schematic sectional view of a reflection type liquid crystal display device having a front light of a side light according to a fifth embodiment of the present invention. Only a main part is shown, and a detailed configuration is omitted.
[0049]
As shown in the drawing, the liquid crystal display panel 21 includes a front light 22 and a frame 23 that supports the liquid crystal display panel 21 and the front light 22. The front light 22 includes a light guide plate 24 having a prism surface on the display surface side, a low gas pressure cold cathode tube 25 and a high gas pressure cold cathode tube 26 disposed at one end of the light guide plate 24, and And a reflector 27 for guiding light from the low-gas pressure cold-cathode tube 25 and the high-gas pressure cold-cathode tube 26 to the light guide plate 24 side.
[0050]
Also in this case, a stable luminance with respect to a temperature change can be obtained as in the above embodiments.
The light guided to the light guide plate 24 is reflected toward the liquid crystal display panel 21 by the prism surface on the display surface side and enters the liquid crystal display panel 21.
[0051]
The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible.
For example, in the above description of the first embodiment, a description has been given of two cold cathode tubes of high gas pressure and low gas pressure, but two or more cold cathode tubes may be arranged in one reflector. Yes, and the same applies to other embodiments.
[0052]
Further, the type of gas pressure is not limited to the two types of the high gas pressure and the low gas pressure, and a discharge tube having three or more types of gas pressures may be used. The same applies to other embodiments. It is.
[0053]
Further, in the fifth embodiment, two types of discharge tubes of high gas pressure and low gas pressure are alternately arranged. May be used, and the order and method of arrangement are not particularly limited.
[0054]
Further, in each of the above embodiments, the main gas in the low-gas-pressure cold cathode tube and the high-gas-pressure cold-cathode tube is Ne and Ar, and the ratio is 97: 3, but the ratio is arbitrary. Yes, and it is not limited to Ne and Ar, and other rare gases such as Kr may be used.
[0055]
Here, the detailed features of the present invention will be described with reference to FIG. 1 again.
Referring again to FIG. 1 (Supplementary Note 1), in a flat light source device in which at least two or more discharge tubes 1 and 2 serving as light sources are arranged, the gas pressure of at least one discharge tube 1 is changed to the gas pressure of another discharge tube 2. A flat light source device characterized by being different from the above.
(Supplementary note 2) The flat light source device according to supplementary note 1, wherein the composition ratio of the main gas sealed in the two or more discharge tubes 1 and 2 is the same in all the discharge tubes 1 and 2.
(Supplementary Note 3) The flat light source device according to Supplementary Note 1 or 2, wherein the flat light source device is a sidelight system using the light guide plate 3.
(Supplementary Note 4) A plurality of discharge tubes 1 and 2 are disposed at both ends of the light guide plate 3, respectively, and at least one of the discharge tubes 1 and 2 is disposed at each end. The flat light source device according to claim 3, wherein the gas pressure is different from the gas pressure of the other discharge tubes 2.
(Supplementary Note 5) The light guide plate 3 is used upright with respect to a horizontal plane, and the gas pressure of the discharge tubes 1 and 2 arranged on the upper end side of the light guide plate 3 and the lower end side of the light guide plate 3 4. The flat light source device according to claim 3, wherein the gas pressures of the discharge tubes 1 and 2 arranged in the light source are different from each other.
(Supplementary note 6) The flat light source device according to supplementary note 1 or 2, wherein the flat light source device is a direct type in which the plurality of discharge tubes 1 and 2 are disposed immediately below a light emitting plane.
(Supplementary note 7) The flat light source device according to supplementary note 6, wherein gas pressures in the plurality of discharge tubes 1 and 2 are different between the discharge tubes 1 and 2 adjacent to each other.
(Supplementary note 8) The flat light source device according to any one of Supplementary notes 1 to 7, wherein the plurality of discharge tubes 1 and 2 are connected to a discharge tube driving circuit by independent electrical connection means. .
(Supplementary note 9) The discharge tube driving circuit according to Supplementary note 8, wherein the discharge tube 1 and the discharge tube 2 having different gas pressures have a function of setting different tube currents or tube voltages according to the respective gas pressures. Flat light source device.
(Supplementary Note 10) A liquid crystal display device comprising the flat light source device according to any one of Supplementary Notes 1 to 9 as a light source.
[0056]
【The invention's effect】
According to the present invention, since the discharge tubes having different gas pressures are used, the light emission luminance of the flat light source device is hardly dependent on the temperature, the luminance change is small even in an environment where the temperature change is large, and the display quality is always high. A good liquid crystal display device can be provided, and a low luminance phenomenon at the beginning of lighting can be reduced, and desired luminance can be achieved in a short time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is a schematic perspective view of a sidelight type backlight according to the first embodiment of the present invention.
FIG. 3 is an explanatory diagram of the temperature dependence of the luminous efficiency of the sidelight type backlight according to the first embodiment of the present invention.
FIG. 4 is a schematic perspective view of a sidelight type backlight according to a second embodiment of the present invention.
FIG. 5 is a schematic perspective view of a sidelight type backlight according to a third embodiment of the present invention.
FIG. 6 is a schematic perspective view of a sidelight type backlight according to a fourth embodiment of the present invention.
FIG. 7 is a schematic perspective view of a direct-type backlight according to a fifth embodiment of the present invention.
FIG. 8 is a schematic sectional view of a reflective liquid crystal display device provided with a sidelight type front light according to a sixth embodiment of the present invention.
FIG. 9 is a cross-sectional view of a main part of a liquid crystal display panel module having a conventional sidelight type backlight.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 discharge tube 2 discharge tube 3 light guide plate 4 reflector 11 light guide plate 12 low gas pressure cold cathode tube 13 high gas pressure cold cathode tube 14 reflector 15 reflector 16 reflector 21 liquid crystal display panel 22 front light 23 frame 24 light guide plate 25 Low gas pressure cold cathode tube 26 High gas pressure cold cathode tube 27 Reflector 31 Liquid crystal display panel 32 Spacer 33 Linear light source 34 Reflector 35 Light guide plate 36 Reflection plate 37 Diffusion plate 38 Shield case

Claims (5)

A flat light source device in which at least two or more discharge tubes as light sources are arranged, wherein the gas pressure of at least one discharge tube is different from the gas pressure of another discharge tube. 2. The flat light source device according to claim 1, wherein the flat light source device is a side light type using a light guide plate. The flat light source device according to claim 1, wherein the flat light source device is a direct type in which the plurality of discharge tubes are disposed immediately below a light emitting plane. 4. The flat light source device according to claim 1, wherein the plurality of discharge tubes are connected to a discharge tube driving circuit by independent electrical connection means. 5. A liquid crystal display device comprising the flat light source device according to any one of claims 1 to 4 as a light source.

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