JPH10333142A - Back light and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the stable luminance property of a fluorescent lamp in a wide temperature range. SOLUTION: A double-tube structure fluorescent lamp 3 is arranged so as to be bent and formed nearly at a right angle along at least two adjacent end faces of a light guide unit 2 for leading incident light entering from the end face to a light emitting surface 2a and to improve the luminance rise-up property at a low temperature. Then, a radiation member 16 having excellent thermal conductivity is installed on the bent part of the fluorescent lamp 3 to urge the radiation of the fluorescent lamp 3 and to suppress the reduction of the luminance of the fluorescent lamp when the atmosphere temperature rises. Thus, the stable luminance property is obtained in a wide temperature range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight using a double-tube fluorescent lamp and a liquid crystal display using the same.

[0002]

2. Description of the Related Art Generally, a backlight used as a back light for a liquid crystal display or a vehicle-mounted meter has a fluorescent lamp opposed to an end face of a light guide unit, and light from the fluorescent lamp is applied to an end face of the light guide unit. The structure is such that the light is incident and the incident light is guided to the light emitting surface of the light guide unit.

FIG. 10 is a front view showing an example of a conventional backlight. The backlight 101 shown in FIG.
The light guide unit 102 and the light source unit 103 are formed by being housed in one housing 104. The light guide unit 102 has a structure for guiding incident light from the end face to the light emitting surface 102a, and mainly includes a light guide plate (not shown), a reflection sheet (not shown) on the back side of the light guide plate, and a not-shown sheet on the front side. The light-collecting sheet and the diffusion sheet 105 are formed by bonding and fixing. Also, the light source unit 103
Mainly comprises a fluorescent lamp 106 which is disposed along two adjacent end faces of the light guide unit 102 and which is bent at a substantially right angle, and which transmits light from the fluorescent lamp 106 to the light guide unit 10.
2, a light source cover (not shown) for guiding to the end face, a backlight cover 107 integrated with the housing 104, and the like.

[0004]

Generally, in a fluorescent lamp, the luminance rising characteristic tends to deteriorate as the ambient environment becomes lower in temperature. Therefore, when the backlight is used in a low-temperature atmosphere, the backlighting function is not sufficiently performed when the backlight is started. Therefore, the inventors of the present invention focused on the fact that the fluorescent lamp of the double tube structure can keep the mercury vapor pressure in the tube in a stable state even in a low temperature atmosphere, and used the fluorescent lamp of the double tube structure as the fluorescent lamp of the backlight. I tried using it. Here, the double-tube fluorescent lamp has a structure in which the arc tube is hermetically covered with an outer tube such as a glass tube, and the pressure between the arc tube and the outer tube is reduced. According to the fluorescent lamp having such a double tube structure, a heat insulating effect is generated between the arc tube and the outer tube which are in a reduced pressure atmosphere, and the characteristics of the fluorescent lamp are exhibited without being affected by the ambient temperature of the outside air. Will be.

However, in a fluorescent lamp having a double tube structure,
In an atmosphere at a temperature lower than 0 ° C., effective characteristics, for example, brightness rise characteristics tend to be easily obtained, whereas in a high-temperature atmosphere, the temperature of the arc tube rises excessively, thereby increasing the internal mercury vapor pressure. In some cases, the brightness of the fluorescent lamp may increase and the brightness of the fluorescent lamp may decrease. Further, in the backlight, for example, as in the backlight 101 shown in FIG. 10, the fluorescent lamp is housed in a narrow space in the housing, so that the temperature of the fluorescent lamp at the time of lighting is higher than that of the fluorescent lamp alone. There is a problem in that the brightness increases and the brightness greatly decreases. FIG. 11 is a graph showing the relationship between the ambient temperature (ambient temperature of the fluorescent lamp) in the backlight and the relative luminance of the fluorescent lamp. As shown in FIG. 11, the relative luminance of the fluorescent lamp, which was 100% when the ambient temperature was 0 ° C. or lower, became 80% when the ambient temperature became about 25 ° C.
It falls to a weak degree.

An object of the present invention is to provide a backlight capable of obtaining stable luminance characteristics of a fluorescent lamp in a wide temperature range and a liquid crystal display device using the same.

[0007]

A backlight according to claim 1 has a rectangular shape and guides light incident from an end face to a light emitting surface; and a light guide unit having at least two end faces adjacent to the light guide unit. A fluorescent lamp having a double-tube structure, which is bent and formed; and a heat radiating means provided at a bent portion of the fluorescent lamp to promote heat radiation of the fluorescent lamp.

Here, the "light guide unit" has, for example, a structure in which a light guide plate is mainly used, a reflection plate is provided on the back surface side of the light guide plate, and a condensing diffusion plate is provided on the front surface side. Light from the light source to the light emitting surface. As the light guide plate, for example,
A flat plate made of an acrylic resin is used. The reflection plate and the light-condensing diffusion plate are formed, for example, in a sheet shape, and are adhered and fixed to the light guide plate. The “double tube structure fluorescent lamp” has a structure in which an arc tube is hermetically covered with an outer tube such as a glass tube, and a vacuum or reduced-pressure atmosphere is maintained between the arc tube and the outer tube.
The "radiator" is formed by "metal" (claim 2) or "resin" (claim 3) or "opening provided in the backlight cover" (claim 4). When `` metal '' is used as the heat radiating means, the heat radiating means is, for example, formed in a plate shape and wrapped or attached around the fluorescent lamp, or formed in a linear shape and wrapped around the fluorescent lamp, Alternatively, it is formed in a cylindrical shape, fitted to the fluorescent lamp, and bent together with the fluorescent lamp. In addition, "resin" as a heat radiation means, for example,
Silicon resin or the like applied around the fluorescent lamp.
Further, the “backlight cover” may be formed integrally with the housing of the backlight, for example. By using such heat dissipating means as "metal", "resin", or "opening provided in the backlight cover", the heat dissipating means is easily provided, and the production is facilitated.

Therefore, in the backlight according to the first aspect, when the fluorescent lamp is turned on, light enters the light guide unit from at least two end faces, and the incident light is guided in the light guide unit and its light emitting surface. Emitted from This illuminates the back surface of the object placed opposite the light emitting surface of the light guide unit. At this time, since a fluorescent lamp having a double tube structure is used, a heat insulating effect is produced between the arc tube and the outer tube in a vacuum or reduced-pressure atmosphere, and the luminance rising characteristics at low temperatures are improved. Further, since the heat radiating means is provided at the bent portion of the fluorescent lamp, a decrease in luminance when the ambient temperature is increased is suppressed, and stable luminance characteristics can be obtained in a wide temperature range. Here, since the arc tube and the outer tube are close to or in contact with each other at the bent portion of the fluorescent lamp, the effect of suppressing the decrease in luminance by the heat radiating means works well. Moreover,
Since the bent portion of the fluorescent lamp may be a portion where the amount of light incident on the light guide unit may be small, the adverse effect on the optical characteristics of the backlight is small even when the heat radiating means does not have light transmittance.

According to a fifth aspect of the present invention, there is provided a liquid crystal display device comprising: a transmissive liquid crystal display element; and a backlight according to any one of the first to fourth aspects disposed on a non-light emitting surface side of the transmissive liquid crystal display element. And a housing for holding a transmissive liquid crystal display element and a backlight. The backlight according to any one of claims 1 to 4 has a stable luminance characteristic over a wide temperature range, so that stable display quality can be obtained on the liquid crystal display surface.

[0011]

FIG. 1 shows a first embodiment of the present invention.
A description will be given with reference to FIG. FIG. 1 is a front view of a backlight, FIG. 2 is a horizontal sectional view showing a part of a liquid crystal display device,
FIG. 3 is a vertical cross-sectional view showing an enlarged part of a fluorescent lamp having a double tube structure, FIG. 4 is a perspective view showing a bent portion of the fluorescent lamp together with a heat radiating means, and FIG. 4 is a graph showing a relationship between the relative luminance of the fluorescent lamp and the relative luminance.

A flat housing-like housing 1 has a backlight 4 mainly composed of a flat rectangular light guide unit 2 and a fluorescent lamp 3 bent in an L-shape, and the backlight 4 has a non-light emitting surface. The transmission type liquid crystal display element 5 which illuminates the side 5b is accommodated therein.
(See FIGS. 1 and 2). Here, since the area of the light guide unit 2 is smaller than the area of the housing 1, an L-shaped space is formed inside the housing 1 at a portion where the light guide unit 2 is not arranged, and the fluorescent lamp 3 is arranged at this portion. ing. Therefore, the fluorescent lamp 3
The light guide unit 2 is arranged along two adjacent end faces.

Light guide unit 2 constituting backlight 4
Has a structure in which light incident from an end face is guided to its light emitting surface 2a. The light guide plate 7 is mainly composed of an acrylic resin light guide plate 7 whose light emitting surface emits light by the incident light from the end face. The reflection sheet 8 is bonded and fixed, and the light collector 9 and the diffusion plate 10 are arranged and formed on the front side (FIG. 2).
reference). In such a light guide unit 2, the reflection sheet 8 plays a role of reflecting light in the direction of the surface of the light guide plate 7, and the light collector 9 and the diffusion plate 10 convert the light guided to the surface of the light guide plate 7 into parallel light. And plays the role of emitting light to the outside. In the backlight 4, the fluorescent lamp 3 is disposed so as to face the end face of the light guide plate 7, and a lamp cover 11 is provided at a position covering the fluorescent lamp 3 (see FIG. 2). The lamp cover 11 has a U-shaped cross section so that its end fits on the front and back surfaces of the light guide plate 7, and has a reflective surface 12 formed on the inner surface thereof. The reflection surface 12 is made of a high light reflective material such as aluminum or silver.

The fluorescent lamp 3 constituting the backlight 4
Has a double tube structure (see FIGS. 2 and 3). That is, in the fluorescent lamp 3, the arc tube 14 having the cold cathode electrodes 13 at both ends is hermetically covered with the outer tube 15 such as a glass tube, and the space between the arc tube 14 and the outer tube 15 is maintained in a substantially vacuum state. Of structure. In order to cover the arc tube 14 with the outer tube 15 in an airtight manner, in the fluorescent lamp 3 of the present embodiment, the end of the outer tube 15 is welded to the end of the arc tube 14. Such a fluorescent lamp 3 is formed in a straight tube shape and then bent at a right angle.

[0015] Then, as shown in FIG.
Is provided with a heat radiating member 16 as a heat radiating means. As illustrated in FIG. 4, various examples of the heat radiating member 16 include a metal plate member 16a wound or attached to the fluorescent lamp 3 (FIG. 4).
(A)), a metal linear member 16b wound around the fluorescent lamp 3 (FIG. 4 (b)), a metal cylindrical member 16c
The cylindrical member 16c is bent together with the fluorescent lamp 3 after fitting the straight tube-shaped fluorescent lamp 3 before bending (FIG. 4C), or the fluorescent lamp 3 is made of silicone resin or the like. It is formed by applying resin 16d (FIG. 4D) or the like.

Further, the housing 1 has an opening 1
The light-guiding unit 2 is arranged with the light-emitting surface 2a facing the light-emitting unit 2a. Installed. Therefore, the light emitting surface 5 a of the transmissive liquid crystal display element 5 is arranged so as to be exposed to the front of the backlight 4. The housing 1 also serves as a backlight cover that covers the fluorescent lamp 3. FIG.
Although the backlight cover is shown only on the rear side of the housing 1, a backlight cover for covering the fluorescent lamp 3 is also provided on the front side of the housing 1.

In such a structure, when the fluorescent lamp 3 is turned on at the time of driving and displaying the transmissive liquid crystal display element 5, light from the arc tube 14 is incident on the light guide plate 7 from the end face. The incident light is reflected by the reflection sheet 8, is aligned in parallel by the light collector 9 and the diffusion plate 10, and is emitted into the non-light-emitting surface 5 b of the transmissive liquid crystal display element 5 with its emission direction determined. Thus, the image displayed by the transmissive liquid crystal display element 5 driven based on the image data is displayed on the backlight 4.
It is displayed brightly in the light of.

At the time of operation of the backlight 4, since the fluorescent lamp 3 has a double tube structure, a heat insulating effect is produced between the arc tube 14 and the outer tube 15 which are almost in a vacuum state, The luminance rising characteristics at the time are improved. Moreover, since the heat radiation member 16 is provided at the bent portion of the fluorescent lamp 3, a decrease in luminance when the ambient temperature rises is suppressed, and stable luminance characteristics can be obtained in a wide temperature range. That is, as shown in the graph of FIG. 5 showing the relationship between the ambient temperature of the backlight 4 (ambient temperature of the fluorescent lamp 3) and the relative luminance of the fluorescent lamp 3, when the ambient temperature is 0 ° C., 100%
The relative luminance of the fluorescent lamp was 25 ° C.
Even if it becomes smaller, it is maintained at less than 90%. This is because, at the bent portion of the fluorescent lamp 3, the arc tube 14 and the outer tube 15 are close to or in contact with each other, so that the effect of suppressing the decrease in luminance by the heat radiation member 16 works well. In addition, even when the heat radiating member 16 does not have light transmittance, the backlight
Adverse effect on the optical properties of This is because the bent portion of the fluorescent lamp 3 is a portion where the amount of light incident on the light guide unit 2 may be small.

FIG. 6 is a horizontal sectional view showing a part of a liquid crystal display device as a first modification. In a first modification,
As the fluorescent lamp 3, a lamp in which the arc tube 14 is eccentric from the center of the fluorescent lamp 3 is used. The eccentric direction is a direction approaching the light guide plate 7 of the light guide unit 2.
Thereby, the distance from the arc tube 14 to the light incident end face of the light guide plate 7 is shortened, and the efficiency of light incidence on the light incident end face of the light guide plate 7 is improved. As a result, the brightness of the backlight 4 increases.

FIG. 7 is a horizontal sectional view showing a part of a liquid crystal display device as a second modification. In a second modification,
Not only is the fluorescent lamp 3 whose luminous tube 14 is decentered from the center of the fluorescent lamp 3 toward the light incident end face of the light guide plate 7, but also the lamp cover 11 is arranged close to the light guide plate 7. That is, the lamp cover 11 is arranged such that the reflection surface 12 thereof comes into contact with the fluorescent lamp 3. As a result, the distance from the reflecting surface 12 of the lamp cover 11 to the light incident end face of the light guide plate 7 is reduced, and the arc tube 14
The light incident on the light incident end face of the light guide plate 7 with respect to the light reflected from the reflecting surface 12 of the lamp cover 11 is also improved. As a result, the brightness of the backlight 4 increases.

A second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a front view of the housing 1 (backlight cover), and FIG. 9 is a rear view thereof. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted. In the present embodiment, the heat radiation member 16 is not provided at the bent portion of the fluorescent lamp 3 and the housing 1
At the position corresponding to the bent portion of the fluorescent lamp 3 in the (backlight cover), an opening 21 as a heat radiating means is provided. The openings 21 are formed on the front side and the back side of the housing 1, respectively.

In such a configuration, the backlight 4
During the operation, the fluorescent lamp 3 has a double tube structure, so that the light emitting tube 14 and the outer tube
5, a heat insulating effect is generated, and the luminance rising characteristics at low temperatures are improved. Since the opening 21 as a heat radiating means is provided at a position corresponding to the bent portion of the fluorescent lamp 3, a decrease in the brightness of the fluorescent lamp 3 when the ambient temperature rises is suppressed, and the backlight 4 has a wide temperature range. A stable luminance characteristic can be obtained in the range. That is, as shown in the graph of FIG. 5 showing the relationship between the ambient temperature in the backlight 4 (the ambient temperature of the fluorescent lamp 3) and the relative luminance of the fluorescent lamp 3, when the ambient temperature was 0 ° C., it was 100%. The relative luminance of the fluorescent lamp is maintained at less than 90% even when the ambient temperature is about 25 ° C. This is because, at the bent portion of the fluorescent lamp 3, the arc tube 14 and the outer tube 15 are close to or in contact with each other, so that the effect of the heat radiation by the opening 21 effectively suppresses the decrease in luminance of the fluorescent lamp 3.

In the embodiment, both the heat radiating member 16 in the first embodiment and the opening 21 in the second embodiment may be provided.

[0024]

According to the backlight of the present invention, a heat radiating means for radiating heat of the fluorescent lamp is provided at a bent portion of the fluorescent lamp having a double tube structure disposed along at least two end faces adjacent to the light guide unit. Therefore, it is possible to suppress a decrease in luminance when the ambient temperature rises. Therefore, stable luminance characteristics can be obtained in a wide temperature range. Further, by forming the heat radiating means from a metal (Claim 2) or a resin (Claim 3), the heat radiating means can be easily provided, and therefore, the production can be facilitated. Further, even when the heat radiating means is formed by an opening provided in the backlight cover (claim 4), the heat radiating means can be easily provided, and therefore, the manufacturing can be facilitated.

According to a fifth aspect of the present invention, there is provided a liquid crystal display device having the backlight according to any one of the first to fourth aspects, which exhibits stable luminance characteristics over a wide temperature range. Obtainable.

[Brief description of the drawings]

FIG. 1 is a front view of a backlight showing a first embodiment of the present invention.

FIG. 2 is a horizontal sectional view showing a part of the liquid crystal display device.

FIG. 3 is a vertical sectional view enlarging a part of a fluorescent lamp having a double tube structure.

FIG. 4 is a perspective view showing a bent portion of the fluorescent lamp together with a heat radiating means.

FIG. 5 is a graph showing a relationship between an ambient temperature (ambient temperature of a fluorescent lamp) in a backlight and a relative luminance of the fluorescent lamp.

FIG. 6 is a horizontal sectional view showing a part of a liquid crystal display device as a first modification.

FIG. 7 is a horizontal sectional view showing a part of a liquid crystal display device as a second modification.

FIG. 8 is a front view of a housing (backlight cover) showing a second embodiment of the present invention.

FIG. 9 is a rear view thereof.

FIG. 10 is a front view of a backlight showing an example of the related art.

FIG. 11 is a graph showing a relationship between an ambient temperature (ambient temperature of a fluorescent lamp) in a backlight and a relative luminance of the fluorescent lamp.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1: Housing, backlight cover 2: Light guide unit 2a: Light emitting surface 3: Fluorescent lamp 4: Backlight 5: Transmissive liquid crystal display element 5b: Non-light emitting surface 6: Liquid crystal display device 16: Heat radiating means 21: Heat radiating means, Opening

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kiyoshi Nishimura 4-3-1 Higashishinagawa, Shinagawa-ku, Tokyo Toshiba Lighting & Technology Corporation

Claims (5)

[Claims] 1. A light guide unit having a rectangular shape and guiding incident light from an end face to a light emitting surface; and a bent double tube arranged along at least two end faces adjacent to the light guide unit. A backlight comprising: a fluorescent lamp having a structure; and a heat radiating means provided at a bent portion of the fluorescent lamp to promote heat radiation of the fluorescent lamp. 2. The backlight according to claim 1, wherein the heat radiating means is made of metal. 3. The backlight according to claim 1, wherein the heat radiation means is a resin. 4. The backlight according to claim 1, wherein the heat radiating means is an opening provided in the backlight cover. 5. A transmissive liquid crystal display element; a backlight according to claim 1, which is disposed on a non-light-emitting surface side of the transmissive liquid crystal display element; A housing for holding the backlight;
A liquid crystal display device comprising: