JP2003242816A - Lighting unit and liquid crystal display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of a fluorescent discharge tube used for a lighting unit, wherein luminance of a liquid crystal display device to be incorporated in the lighting unit very largely depends on temperature, since the fluorescent discharge tube has temperature characteristics in its luminous efficiency. <P>SOLUTION: In a plurality of the fluorescent discharge tubes 8A, 8B of the lighting unit UT, temperature characteristics in the luminous efficiency of each fluorescent discharge tube 8A, 8B are varied by varying either one or more of a gas pressure, a gas composition ratio, or a tube diameter. Or, the electric current of each fluorescent discharge tube 8A, 8B is varied, or the temperature in the vicinity of the fluorescent discharge tubes 8A, 8B is varied by disposing a heat sink 11 in the vicinity of at least one fluorescent discharge tube 8B. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination unit using a plurality of fluorescent discharge tubes and a liquid crystal display device using such an illumination unit.

[0002]

2. Description of the Related Art In recent years, display devices for information devices such as notebook personal computers and word processors, or display devices for video devices such as portable televisions, video movies, car navigation systems, etc.
Liquid crystal display devices have been widely used due to their low power consumption. In many of these liquid crystal display devices, in order to realize a bright display screen, illumination light is applied from the back of the display element by a built-in illumination unit.

In this illumination unit, an edge light system is used in which a light guide plate is placed on the back surface of a display element and a linear fluorescent discharge tube such as a fluorescent discharge tube is arranged on the end surface of the light guide plate.
It has the characteristics of thinness and excellent brightness uniformity of the light emitting surface. As a backlight system for liquid crystal display devices used in notebook personal computers, etc., this edge light system is prioritized for its thinness. Often adopted.
In liquid crystal display devices used in portable televisions, car navigation systems, etc., in order to achieve both thinness and brightness, fluorescent discharge tubes are arranged on both the left and right sides of the light guide plate, and the edge light system or only one side is arranged. In many cases, the edge light method is adopted.

3A and 3B show an edge light type illumination unit UT in which a conventional fluorescent discharge tube is arranged on one side of a light guide plate, and a liquid crystal display device L having the same. As shown in FIG. 3A, the lighting unit UT includes a flat transparent light guide plate 1 for transmitting light to the entire irradiation surface, and a plurality of fluorescent discharge tubes arranged on the side surface of the light guide plate 1. 8A, 8B,
The reflector 7 that guides the light emitted from the fluorescent discharge tubes 8A and 8B to the side surface of the light guide plate 1, the reflector plate 2 that reflects the light traveling to the back surface side of the light guide plate 1, and the light emitted from the light guide plate 1 A resin film sheet 5 for correction and a metal back cover 6 are provided. The light guide plate 1, the reflector 7, and the resin film sheet 5 are held by the housing 3, and the back surfaces of the reflection plate 2 and the reflector 7 are the back cover 6.
Is covered with the housing 3 and the back cover 6 by the screw 4.
And are concluded. In the liquid crystal display device L, as shown in FIG. 3B, a liquid crystal display panel 9 having a liquid crystal layer sandwiched between a pair of substrates 9A and 9B is superposed on the irradiation surface side (upper side in the drawing) of the illumination unit UT. , The metal frame 10 holds them.

In the fluorescent discharge tubes 8A and 8B, mercury and an inert gas are sealed in the tubes, and mercury molecules emit ultraviolet rays due to the discharge between the columnar lamp electrodes, and the ultraviolet rays cause the fluorescent substance applied to the inner wall of the tubes. When excited, it emits visible light. Argon, neon, or the like is used as the inert gas.

[0006]

When the liquid crystal display device is used in a wide variety of applications such as car AVs, mobile phones, notebook PCs, liquid crystal monitors, and liquid crystal televisions, the usage environment, especially the temperature environment, is becoming significantly different. .
On the other hand, a fluorescent discharge tube 8 of a lighting device used for a liquid crystal display device.
In A and 8B, the temperature dependence of the luminous efficiency is governed by the concentration of mercury vapor and the gas pressure that contribute to light emission, and due to this temperature dependence, light emission occurs when the ambient temperature of the fluorescent discharge tubes 8A and 8B is a certain temperature. The efficiency was the highest, and the luminous efficiency was lowered regardless of whether the temperature was higher or lower. That is, in order to obtain a brightness equal to or higher than a certain value, it is necessary to use within a certain temperature range, and when the temperature is out of this temperature range, the brightness is remarkably reduced. Thus, there has been a problem that the temperature dependence of the brightness of the liquid crystal display device is extremely large.

Therefore, an object of the present invention is to improve the brightness by changing the temperature characteristic of the luminous efficiency of the fluorescent discharge tube or the temperature in the vicinity of the fluorescent discharge tube when a plurality of fluorescent discharge tubes are used. An object of the present invention is to provide an illumination unit and a liquid crystal display device that can reduce the temperature dependence of the temperature.

[0008]

In order to solve the above problems, the lighting unit according to claim 1 of the present invention is a lighting unit in which a plurality of fluorescent discharge tubes are used, and at least two of the plurality of fluorescent discharge tubes are used. It is characterized in that any one or two or more of the gas pressure, the gas composition ratio, or the pipe diameter is different between the two.

According to the present invention, the gas pressure of the fluorescent discharge tube,
Since at least two of the plurality of fluorescent discharge tubes have different gas composition ratios or tube diameters, at least one of which is different from each other, the temperature characteristics of the luminous efficiency differ between at least two of them. Therefore, since the temperature characteristics of the luminous efficiency (luminance) of the entire plurality of fluorescent discharge tubes are the sum of the temperature characteristics of the individual fluorescent discharge tubes, the allowable temperature range for the required luminance is widened and the temperature dependence of the luminance is also increased. Can be reduced.

The lighting unit according to a second aspect of the present invention is characterized in that, in a lighting unit in which a plurality of fluorescent discharge tubes are used, the currents flowing between at least two of the plurality of fluorescent discharge tubes are different. .

According to the present invention, since the electric current to be flown is made to differ between at least two of the plurality of fluorescent discharge tubes, the calorific values of these fluorescent discharge tubes are different. As a result, even if the temperature characteristics of the luminous efficiency of the fluorescent discharge tubes are common, since the ambient temperatures of at least two fluorescent discharge tubes are already different from each other, the change in the luminous efficiency is further reduced when the ambient temperature further changes. The method (the direction of increasing or decreasing the brightness) is different. Therefore, in the luminous efficiency (luminance) of the plurality of fluorescent discharge tubes as a whole, the allowable temperature range with respect to the required luminance can be widened.

According to a third aspect of the present invention, in a lighting unit in which a plurality of fluorescent discharge tubes are used, a heat sink is arranged in the vicinity of at least one fluorescent discharge tube instead of the total number.

According to the present invention, by disposing the heat sink near the fluorescent discharge tube, the heat generated in the fluorescent discharge tube can be efficiently dissipated. Therefore, the fluorescent discharge tubes near the heat sink are closer to the external temperature (ambient temperature that is not affected by the heat generated by the fluorescent discharge tubes) than the fluorescent discharge tubes without the heat sink, and the ambient temperatures of these fluorescent discharge tubes are different from each other. . As a result, when the ambient temperature further changes, the way in which the luminous efficiency changes (direction of increasing or decreasing the luminance) becomes different. Therefore, in the luminous efficiency (luminance) of the plurality of fluorescent discharge tubes as a whole, the allowable temperature range with respect to the required luminance can be widened.

According to the liquid crystal display device using the illumination unit according to claim 4 of the present invention, the liquid crystal layer is sandwiched between the pair of substrates on the irradiation surface side of the illumination unit according to claims 1 to 3. It is characterized in that the liquid crystal display panels are stacked.

According to the present invention, since there is little change in the brightness with respect to the change in the ambient temperature in the lighting unit, the temperature dependence of the brightness of the liquid crystal display device can be reduced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) An illumination unit UT of the present embodiment is shown in FIG. 1A, and is a flat transparent light guide plate 1 for transmitting light to the entire irradiation surface, and the light guide plate 1. A plurality of fluorescent discharge tubes 8A and 8B arranged on the side surface of the light plate 1, a reflector 7 that guides the light emitted from the fluorescent discharge tubes 8A and 8B to the side surface of the light guide plate 1, and travels to the rear surface side of the light guide plate 1. The light guide plate 1 is provided with a reflection plate 2 for reflecting the reflected light, a resin film sheet 5 for correcting the light emitted from the light guide plate 1, and a metal back cover 6. The light guide plate 1, the reflector 7, and the resin film sheet 5 are held by the housing 3, and the back surfaces of the reflection plate 2 and the reflector 7 are covered with a back cover 6.
The housing 4 and the back cover 6 are fastened by the screws 4.

The light guide plate 1 is made of a material such as acryl, which has optimum optical characteristics represented by the transmittance and the refractive index required for light transmission. The light guide plate 1 includes a fluorescent discharge tube 8
A dot pattern or groove pattern (not shown) whose shape is changed according to the distance from A and 8B is provided on the back surface.

The reflector 7 reflects the light of the fluorescent discharge tubes 8A and 8B and allows the light to efficiently enter the side surface of the light guide plate 1, and is made of a white resin film having a high reflectance, silver, aluminum or the like. A metal film is used and is bent in a U-shaped cross section or a U-shaped cross section so as to surround the fluorescent discharge tubes 8A and 8B.

The reflection plate 2 has a role of increasing the illumination light emitted by returning the light emitted from the back surface of the light guide plate 1 back into the light guide plate 1, and extends along the back surface of the light guide plate 1. It is located in. As the reflector 2, a white resin film having a high reflectance is used. There is also one in which one side of the reflection plate 2 is bent in a U-shape or a horizontal U-shape so as to surround the fluorescent discharge tubes 8A and 8B, and a reflector 7 integrally formed with the reflection plate 2 is formed. .

The housing 3 is disposed close to the side surface of the reflector 7 so as to surround it from above. Housing 3
Serves as a holder for the lighting unit UT and also has a role of holding the liquid crystal display panel 9 and the lighting unit UT. The housing 3 is made of, for example, polycarbonate resin.

The fluorescent discharge tubes 8A and 8B are fluorescent discharge tubes which emit light when driven by a high frequency alternating current (40 to 100 kHz). The fluorescent discharge tubes 8A and 8B according to the present embodiment are arranged in two on one side surface of the light guide plate 1, but two or more are arranged, or a plurality of pieces are arranged on the left and right side surfaces of the light guide plate 1. Alternatively, there is a light guide plate 1 having L-shaped arrangement on two sides of the four sides (referred to as “L-shaped fluorescent discharge tube”) and the like, and both are called edge light type. In the present embodiment, the two fluorescent discharge tubes 8A and 8B have different mercury vapor gas pressures. Therefore, the temperature characteristics of the luminous efficiency of the fluorescent discharge tubes 8A and 8B are different, and the temperatures at which the luminous efficiency shows a peak (optimum temperature) are also different. That is, since the amount of ultraviolet radiation of mercury molecules at a certain temperature is different in each fluorescent discharge tube 8A, 8B, the two fluorescent discharge tubes 8A, 8B appear to have different brightness.

Further, the liquid crystal display device L of the present embodiment is
As shown in FIG. 1B, the liquid crystal display panel 9 is superposed on the irradiation surface side (upper side in the drawing) of the illumination unit UT, and is held by a metal frame 10. The liquid crystal display panel 9 displays characters and images, and has a pair of transparent substrates 9A and 9A on which display electrodes are laid.
B are opposed to each other at appropriate intervals, and a liquid crystal material is sealed at the intervals around the transparent substrates 9A and 9B with a sealing material. The liquid crystal display panel 9 of the present embodiment is called a transmissive type, and by irradiating light from the back side (downward in the figure), the characters and images displayed on the display surface are in a visible state.

In the liquid crystal display device L of this embodiment, the operating temperature is assumed to be about 0 ° C to 40 ° C. Therefore, by changing the gas pressure of mercury vapor so that the temperatures at which the luminous efficiencies of the two fluorescent discharge tubes 8A and 8B reach their peaks (called peak temperatures) are about 15 ° C. and 25 ° C., respectively, In the entire fluorescent discharge tubes 8A and 8B, the temperature range in which the required brightness is obtained is set to 0 ° C to 40 ° C. That is, when the ambient temperature is about 0 ° C. to 20 ° C., the fluorescent discharge tube 8A having a peak temperature of 15 ° C. emits light with a brightness sufficiently higher than the required brightness within this temperature range, and the fluorescent discharge tube having a peak temperature of 25 ° C. 8B may have a luminance lower than the required luminance at a particularly low temperature within this temperature range, but even in such a case, since the luminance of the fluorescent discharge tube 8A is sufficiently high, two fluorescent discharge tubes 8A are provided. ，
The overall brightness of 8B does not decrease so much. On the other hand, when the ambient temperature is 20 to 40 ° C, the peak temperature is 25
The fluorescent discharge tube 8B at ℃ emits light with a brightness sufficiently higher than the required brightness in this temperature range, and the fluorescent discharge tube 8A at a peak temperature of 15 ° C. has a brightness lower than the necessary brightness at a particularly high temperature in this temperature range. However, even in such a case, since the brightness of the fluorescent discharge tube 8B is sufficiently high, the overall brightness of the two fluorescent discharge tubes 8A and 8B does not decrease so much. In this way, the two fluorescent discharge tubes 8
The combination of A and 8B complements each other in the temperature range where the required brightness is not obtained in individual use. Therefore, the temperature dependence of the brightness of the illumination unit UT is reduced, and the temperature dependence of the brightness on the display surface of the liquid crystal display device L is also reduced.

The fluorescent discharge tubes 8A and 8B of the present embodiment are
Although the gas pressure of mercury vapor is made different, the present invention is not limited to this, and the composition ratio and tube diameter of mercury and an inert gas are made different, or by combining these, the temperature characteristics of luminous efficiency are shown. May be changed from each other.

(Second Embodiment) In the present embodiment, the two fluorescent discharge tubes 8A and 8B in the first embodiment have the same luminous efficiency temperature characteristics, and the currents flowing through them are the same. Is different. This gives 2
Since the heat generation amounts of the fluorescent discharge tubes 8A and 8B are different, the temperatures near the fluorescent discharge tubes 8A and 8B are different from each other. The fluorescent discharge tubes 8A and 8B have different luminous efficiencies depending on the ambient temperature.
The fluorescent discharge tubes 8A and 8B of the book have different luminous efficiencies and have different luminances. The temperature characteristic of the luminous efficiency of the fluorescent discharge tubes 8A and 8B usually has a characteristic that the luminance decreases as the temperature rises or falls at the boundary of the temperature showing the peak luminance.
That is, the temperature at the point where the brightness drops by a certain level from the peak brightness is 2 times higher and lower than the peak temperature.
Exists in place. Here, the brightness required for one fluorescent discharge tube 8A, 8B is calculated from the brightness required for illumination of the liquid crystal display device L, and the fluorescent discharge is performed so that the calculated necessary brightness becomes a value lower than the peak brightness. Tubes 8A and 8B are selected. Next, the temperature range in which the required brightness is obtained is calculated from the temperature characteristics of the luminous efficiency of the fluorescent discharge tubes 8A and 8B. This temperature range has a certain temperature range on the high temperature side and the low temperature side across the peak temperature. Then, at room temperature (the highest temperature during use), the two fluorescent discharge tubes 8
The flowing currents are determined so that A and 8B have a high temperature side temperature and a low temperature side temperature in this temperature range, respectively. Here, when the ambient temperature rises, the current is smaller than the other,
That is, the fluorescent discharge tube 8B, which generates a small amount of heat, approaches the peak brightness as the ambient temperature rises, and thus the brightness increases, while the fluorescent discharge tube 8A, which generates a large amount of heat, separates from the peak brightness, and the brightness decreases. Further, when the ambient temperature decreases, the fluorescent discharge tube 8A having a large heat generation amount increases in brightness as the ambient temperature decreases, and the fluorescent discharge tube 8B having a small heat generation amount decreases in brightness. That is, since the two fluorescent discharge tubes 8A and 8B complement each other in brightness, the overall brightness of the two fluorescent discharge tubes 8A and 8B does not change so much due to changes in ambient temperature.

(Third Embodiment) In the present embodiment, as shown in FIG. 2, fluorescent discharge tubes 8A and 8B and a reflector 7 are provided.
A heat sink 11 is placed between
1 is extended along the reflector 7 and brought into contact with the back surface cover 6 on the back surface side (lower side in the drawing). At this time, the heat sink 11 is arranged in the vicinity of only one of the two fluorescent discharge tubes 8A and 8B. When the fluorescent efficiency of the two fluorescent discharge tubes 8A and 8B has the same temperature characteristics and the same current is applied, the amounts of heat generated by the fluorescent discharge tubes 8A and 8B are equal, but the fluorescent discharges in the vicinity of the heat sink 11 are the same. Since the tube 8B can dissipate heat efficiently, the other fluorescent discharge tube 8A
The temperature in the vicinity becomes lower than. As a result, under the condition that the ambient temperature is constant, the temperatures near the two fluorescent discharge tubes 8A, 8B are different, and the two fluorescent discharge tubes 8A, 8B,
The brightness of 8B is different. The heat sink 11 has a property of efficiently conducting the heat generated by the heating elements (fluorescent discharge tubes 8A, 8B), conducts heat to the metallic back cover 6, and radiates heat from the surface of the back cover 6 to the outside air. ing. That is, the heat sink 11 acts so that the heating element has the same temperature as the ambient temperature (the temperature of the outside air), while the temperature in the vicinity of the fluorescent discharge tube 8A where the heat sink 11 is not located is always higher than the ambient temperature. Along with the change in ambient temperature, the temperatures around the two fluorescent discharge tubes 8A and 8B change while remaining different. Here, as in the second embodiment, the temperature range in which a predetermined brightness is obtained is calculated, and the ambient temperature of the two fluorescent discharge tubes 8A and 8B (not the temperature in the vicinity).
Maintain the necessary brightness at room temperature (the highest temperature during use), the temperature near the fluorescent discharge tube 8A is the temperature on the high temperature side within the temperature range, and the temperature near the fluorescent discharge tube 8B is the low temperature within the temperature range. The heat generation amounts of the two fluorescent discharge tubes 8A and 8B and the heat radiation amount of the heat sink 11 are set so that the temperature becomes the side temperature. As a result, when the ambient temperature changes, the two fluorescent discharge tubes 8A and 8B complement each other in brightness, and the temperature dependence of brightness can be reduced.

In each of the above embodiments, the case where two fluorescent discharge tubes 8A and 8B are used as one set has been described, but three fluorescent discharge tubes 8A and 8B are used as one set. Also in this case, the same effect can be obtained by making the temperature characteristics of at least two fluorescent discharge tubes 8A and 8B different from each other or the neighboring temperatures. Further, if the temperature characteristics of the three or more fluorescent discharge tubes 8A and 8B or the temperatures in the vicinity thereof are made slightly different from each other, the temperature dependence of the brightness can be further reduced. In addition, one side of the light guide plate 1 has a fluorescent discharge tube 8A,
8B has been described, the present invention is directed to the light guide plate 1.
It can be generally applied to an edge light system such as a type in which the fluorescent discharge tubes 8A and 8B are arranged on both sides of, and a type in which the fluorescent discharge tubes 8A and 8B are arranged in an L shape. Further, the method of calculating the current in each of the embodiments has been described briefly, and a design margin (margin) or the like may be appropriately provided in the calculation process, or the fluorescent discharge tube 8A and the fluorescent discharge tube 8B may be set. It is optional to set the temperature characteristics and the temperature ranges to be interchanged with each other (for example, to dispose the heat sink 11 in the vicinity of the fluorescent discharge tube 8A). Further, the liquid crystal display panel 9 is not limited to the transmissive type, but may be applied to a reflective type or a semi-transmissive type. At this time, the illumination unit UT is attached to the liquid crystal display panel 9
It is placed on the display side of and used as a front light.

[0029]

According to the lighting unit of the present invention, at least two of the plurality of fluorescent discharge tubes have a gas pressure of
Since one or more of the gas composition ratios or the tube diameters are made different, the temperature characteristics of the luminous efficiency of each fluorescent discharge tube become different, and therefore each fluorescent light is changed against ambient temperature changes. The discharge tube complements the brightness, and the temperature dependence of the brightness can be reduced. In addition, at least two of the plurality of fluorescent discharge tubes have different currents, or at least one of the plurality of fluorescent discharge tubes is used.
By disposing a heat sink near the book, the temperature near each fluorescent discharge tube can be made different. As a result, each fluorescent discharge tube complements the brightness with respect to the ambient temperature change, and the temperature dependence of the brightness can be reduced. Further, by stacking these illumination units on the liquid crystal display device, it is possible to reduce the temperature dependence of the luminance on the display surface of the liquid crystal display device.

[0030]

[Brief description of drawings]

FIG. 1A is a cross-sectional view of a lighting unit according to first and second embodiments of the invention, and FIG. 1B is a first and second embodiments of the invention.
View showing the liquid crystal display device according to the embodiment of FIG.

2A is a sectional view showing an illumination unit according to a third embodiment of the present invention, and FIG. 2B is a sectional view showing a liquid crystal display device according to the third embodiment of the present invention.

FIG. 3A is a sectional view showing a conventional lighting unit, and FIG.
Sectional view showing a conventional liquid crystal display device

[Explanation of symbols]

1 Light guide plate 2 reflector 3 housing 4 screws 5 Resin film sheet 6 back cover 7 reflector 8A, 8B fluorescent discharge tube 9 Liquid crystal display panel 10 metal frame 11 heat sink

Claims (4)

[Claims] 1. A lighting unit using a plurality of fluorescent discharge tubes, wherein at least two of the plurality of fluorescent discharge tubes are provided with at least one of gas pressure, gas composition ratio, or tube diameter. An illumination unit that is different from the above. 2. An illumination unit in which a plurality of fluorescent discharge tubes are used, wherein a current flowing between at least two of the plurality of fluorescent discharge tubes is different. 3. A lighting unit in which a plurality of fluorescent discharge tubes are used, characterized in that a heat sink is arranged in the vicinity of at least one fluorescent discharge tube instead of the total number. 4. A lighting unit according to any one of claims 1 to 3, wherein a liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates is stacked on the irradiation surface side of the lighting unit. Liquid crystal display device used.