JPH07211289A - Back light - Google Patents

Abstract

PURPOSE:To improve the light emitting efficiency of a discharge lamp in a high tube current range by widening the surface area of a lamp holder to give the heat radiating function. CONSTITUTION:A discharge lamp 1 is arranged in one end of a transparent light transmitting body 3, and the inner surface of the tube 1 is surrounded by a lamp holder 2 coated with a reflecting sheet 5, and while the lamp holder 2 is extended to the back surface of the sheet 5. The lamp holder 2 is made of the metal having excellent heat conductivity such as aluminum and copper to give the heat radiating characteristic to the holder 2 itself. The temperature in the surroundings of the tube 1 is lowered by giving the beat radiating characteristic to the holder 2. Consequently, lowering of the light emitting efficiency of the tube 1 in a high tube current range can be prevented, and as a result, high luminance can be efficiently obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight.

[0002]

2. Description of the Related Art The basic structure of a conventional backlight is shown in FIG.
2 and a partially enlarged view thereof, respectively. 1 and 2 show a straight discharge tube 1 such as a cold cathode tube or a hot cathode tube, which serves as a light source, at least at one end of a transparent light guide 3 made of acrylic, depending on the brightness required. Place and
The backlight has a structure in which the diffusion sheet 4 arranged on the front surface emits surface light.

By covering the back surface of the discharge tube 1 with a U-shaped lamp holder 2 provided with a light reflector inside, the light emitted radially from the discharge tube 1 is effectively introduced into the light guide surface of the light guide 3. Are collected in.

The light incident on the light guide body 3 is transmitted while being repeatedly reflected inside the light guide body, and the reflection sheet 5 and the light guide body 3 arranged on the back surface of the light guide body 3 are transmitted during the transmission. Diffuse with a reflective dot pattern previously formed on the back surface by a printing method or the like, and head toward the diffusion sheet. This light is transmitted and diffused by the diffusion sheet 4, and finally the radial light emitted from the discharge tube 1 is converted into surface emission.

The brightness of the discharge tube 1 is adjusted by adjusting the tube current by the inverter circuit connected to both ends of the discharge tube 1, and the required brightness as a backlight is obtained.

The ambient temperature dependence of the brightness of the discharge tube, which is important in explaining the present invention, will be described. FIG. 3 is a representative characteristic diagram of the ambient temperature dependence of the luminance of the tube, which is an example of a cold cathode tube having a diameter of 3 mm which is frequently used as a backlight for liquid crystal display devices, and is shown as a relative value with respect to the ambient temperature of 25 ° C.

It shows that the luminous efficiency is lowered at the peak temperature of 40 ° C. and above the ambient temperature. Although there are some differences depending on the shape of the tube and the tube current, all common cold cathode tubes show the same tendency. That is, in order to efficiently emit light from the discharge tube, it is necessary to design the ambient temperature of the discharge tube to the optimum temperature.

FIG. 4 shows changes in the tube wall temperature of the discharge tube alone with respect to the tube current and changes in the surface temperature of the lamp holder when incorporated in the backlight. This discharge tube has a diameter of 3 m
The lamp holder is a U-shaped product made of aluminum with a cold cathode tube of m and 220 mm in length.

In the case of a single cold-cathode tube, the temperature of the tube wall in the central portion is not significantly affected by the change in the tube current, but the temperature change in the electrode portion is remarkable. Further, the surface temperature of the central portion of the lamp holder when the cold cathode tube is incorporated into the lamp holder and brought into the backlight state is higher than the temperature of the central portion of the cold cathode tube alone. This is because the natural cooling of the cold cathode tube itself has been lost and there is heat conduction from the electrode part. The surface temperature of the central portion of the lamp holder can be generally regarded as the ambient temperature of the cold cathode fluorescent lamp. If the ambient temperature dependence of the brightness of the discharge tube described in FIG. 4 is applied to this, a decrease in brightness may occur at a tube current of 5 mA or more.

In order to confirm the above, FIG. 5 shows a relative comparison result obtained by measuring the change in luminous efficiency with respect to the tube current in the conventional backlight. The luminous efficiency here is the brightness of the backlight surface light source per unit power consumption of the inverter. As a result of the measurement, when the tube current of 4.5 mA reaches the peak and the tube current is flowed any more, the luminous efficiency tends to decrease, and it is necessary to control the ambient temperature of the lamp in order to efficiently obtain a high-brightness surface light source. Was backed up.

[0011]

In the conventional backlight, the tube current was increased as a means for obtaining high brightness, but the heat generated in the discharge tube accompanied by this increased the ambient temperature of the discharge tube, and the discharge tube was heated. The optimum temperature for luminous efficiency may be exceeded. In this case, there is a problem in that it is not possible to obtain an increase in brightness commensurate with power consumption.

[0012]

In order to solve the above problems, the present invention provides a lamp holder with a heat radiation function.

[0013]

By introducing the backlight according to the present invention, an efficient high brightness surface light source can be obtained.

[0014]

Embodiment 1 The present invention will be specifically described below with reference to the drawings. The parts having the same functions as those of the conventional backlight shown in FIGS. 1 and 2 are designated by the same reference numerals. 6 and 7 are basic structural diagrams of a backlight according to an embodiment of the present invention. In FIG. 6, the lamp holder 2 is extended on the back surface of the reflection sheet 5. In FIG. 7, the lamp holder 2 is bent on the back surface of the backlight and extended to the side surface of the backlight. The basic structure and principle of forming the surface light source in any of the backlights is the same as that of the conventional backlight, but the lamp holder 2 is made of aluminum having excellent heat conductivity.
It was made of metal such as copper, and the lamp holder itself had a heat dissipation function.

A backlight having the structure shown in FIG. 7 was prototyped and the effect of the present invention was confirmed. One cold cathode discharge tube having a diameter of 3 mm and a length of 220 mm was arranged on the long side of a light guide for 9.5 inches having a thickness of 4 mm, and the surface light source luminance was measured with respect to the lamp holder shape dependency. According to the shape of the lamp holder of the present invention, the heat dissipation plate is formed so that the surface temperature of the central portion of the lamp holder becomes 50 ° C. when the tube current is 7 mA. The comparison result is shown in FIG. The effect of the present invention is exhibited when the tube current is in the range of 4.75 mA or more, and in particular, at 7 mA, the surface brightness is obtained about 10% higher than that of the conventional backlight, that is, the lamp holder without the heat radiating plate.

[0016]

[Embodiment 2] FIG. 9 shows an embodiment of the present invention in which the lamp holder 2 is corrugated on the side surface of the discharge tube 1 so as to have a heat radiation function. Also in the lamp holder structure of FIG. 9, the effect of heat radiation was obtained as in Example 1, and high brightness could be obtained with high efficiency in the high tube current range.

[0017]

Third Embodiment FIG. 10 shows an embodiment of the present invention in which a lamp holder is fixed to a metal structure of a liquid crystal display device. In FIG. 10, the lamp holder 2 is bent on the back surface of the backlight, extended to the side surface of the backlight, and fixed to the electromagnetic shielding plate 7 of the liquid crystal display device with screws. With this structure, the same effect as in Examples 1 and 2 was obtained.

[0018]

As described above, according to the present invention, the lamp holder is provided with a heat radiation function to lower the ambient temperature of the discharge tube and to reduce the luminous efficiency of the discharge tube in a high tube current range. It is possible to realize a backlight that can be prevented and, as a result, can efficiently obtain high brightness. Furthermore, the present invention is an extremely effective means for a large-sized, high-brightness backlight that requires high power.

[Brief description of drawings]

FIG. 1 is a basic structural diagram of a conventional backlight.

FIG. 2 is a partially enlarged view of a basic structure diagram of a conventional backlight.

FIG. 3 is a representative characteristic diagram of tube brightness with respect to ambient temperature of a cold cathode tube.

FIG. 4 is a representative characteristic diagram of the surface temperature of the cold cathode tube and the lamp holder with respect to the tube current.

FIG. 5 is a representative characteristic diagram of light emission efficiency with respect to a tube current of a backlight.

FIG. 6 is a structural diagram of a backlight showing an embodiment of the present invention, and is a structural diagram in which a lamp holder is particularly extended on the back surface of a reflection sheet.

FIG. 7 is a structural view of a backlight according to an embodiment of the present invention, particularly a structural view in which a lamp holder is bent on the back surface of the backlight and extended to the side surface of the backlight.

FIG. 8 is a characteristic diagram of the surface luminance with respect to the tube current of the backlight showing the effect of the present invention.

FIG. 9 is a structural view of a backlight according to an embodiment of the present invention, particularly a structural view in which a lamp holder is bent into a corrugated shape on a side surface of a discharge tube.

FIG. 10 is a structural view of a backlight according to an embodiment of the present invention, in which the lamp holder is bent at the back surface of the backlight, extended to the side surface of the backlight, and fixed to the electromagnetic shield plate of the liquid crystal display device with screws. is there. 1 to 12
Throughout the drawings, each reference numeral indicates the following.

[Explanation of symbols]

 1: Discharge tube 2: Lamp holder 3: Light guide 4: Diffusion sheet 5: Reflection sheet 6: Electromagnetic shielding plate

Claims (2)

[Claims] 1. A transparent light guide is provided with a discharge tube at least at one end thereof, and the discharge tube is surrounded by a lamp holder having an inner surface covered with a light reflection layer. However, the backlight is characterized by being processed to have a heat dissipation function. 2. The transparent light guide according to claim 1 and a discharge tube, wherein a lamp holder surrounding the discharge tube is fixed to a metal structure of a liquid crystal display device so as to have good heat conduction. And backlight.