KR20080105130A - Underneath backlight - Google Patents

Abstract

When a hot-cathode fluorescent lamp is employed in an underneath backlight, a desirable relation between the number of hot-cathode fluorescent lamps as light sources and respective powers is provided. A liquid crystal panel (20) has a size of a screen (21) equal to diagonal L inch, and a ratio r obtained by dividing the longitudinal length of the screen (21) by the lateral length. An underneath backlight (10) installed on the back of the liquid crystal panel (20) comprises a hot-cathode fluorescent lamp (11) having one substantially linear light emitting section, and a housing (10) for housing the hot-cathode fluorescent lamps in the lateral direction. The number (N) and the power (W) of hot-cathode fluorescent lamps fall within predetermined ranges, respectively. ® KIPO & WIPO 2009

Description

Direct type backlight unit {UNDERNEATH BACKLIGHT}

The present invention relates to a direct type backlight device provided on a rear surface of a liquid crystal panel.

Background Art Display apparatuses such as displays and televisions have conventionally been various methods such as CRT and PDP. In recent years, demands for thinning and large screens of display devices have increased along with saving of power consumption, and liquid crystal displays have become one of the mainstream of display devices.

The liquid crystal display consists of a liquid crystal panel and a backlight device provided on the back of the liquid crystal panel. As the light supplied from the backlight increases, the luminance of the display image required under actual use conditions can be ensured, and a high level of uniformity can be obtained without local lightness or the like when the same image is displayed. It can be set as an optical system.

The direct type backlight device includes a housing in which a surface of the liquid crystal panel side is opened to extract light, and a plurality of fluorescent lamps disposed in the housing. The opening is covered with a resin diffusion plate, a diffusion sheet, a rent sheet and the like (for example, Japanese Patent Laid-Open No. 2001-22285).

In the fluorescent lamp, a cold cathode fluorescent lamp is usually used because it is suitable for thinning and the like.

However, since the cold cathode fluorescent lamp uses a high voltage power supply because the voltage (driving voltage) required for driving is larger than other power supplies, it is necessary to sufficiently insulate the backlight structure.

In recent years, since a large liquid crystal display having a screen size exceeding 26 inches has appeared, the lamp length is longer, and the driving voltage is further increased so that the solution of the above problem is technically difficult and cost increases.

For example, in the conventional 45-inch backlight device, a large output transformer of several kV class is required to drive one lighting circuit for one cold cathode fluorescent lamp, which leads to an increase in cost. In addition, because of the high voltage, current leakage and electromagnetic noise easily occur through the housing or wiring of the backlight device, so that a new member or structure for insulation can be installed, or a voltage of two lamps can be applied to apply a voltage from both ends of the cold cathode fluorescent lamp. It requires double the number of lighting circuits, all of which led to an increase in costs.

In addition, since a cold cathode fluorescent lamp has a small power input per unit, a large number of fluorescent lamps are required to secure screen brightness, thereby increasing the cost of assembly.

That is, since the cold cathode fluorescent lamp has a narrow and long structure with a small lamp diameter, the lamp is easily bent and, when supported only by the sockets on both sides of the lamp, the lamp is struck down by its own weight. It needs a lamp holder to support it. Therefore, in the backlight assembly process, not only the sockets for supplying power to both sides of the lamp but also the work for fixing the lamp to the insertion part of the lamp holder is required. Fixing the lamp must be done carefully so as not to break the cold cathode fluorescent lamp, and in this respect, there was a limit to speeding up the manufacturing process.

In view of these problems, the present inventors have studied to configure a backlight device using a hot cathode fluorescent lamp in place of a conventional cold cathode fluorescent lamp.

However, when the backlight device is configured with the same number and power of the hot cathode fluorescent lamps as the conventional cold cathode fluorescent lamps, it has been found that they cannot be used as devices in terms of lifetime.

According to the inventor's review, the hot cathode fluorescent lamp has a large diameter because it is necessary to arrange the filament coil in the glass tube (the diameter of the cold cathode fluorescent lamp is 12 mm or less, mainly 3 mm or 4 mm. The diameter is 12 mm or more), and the difference in the lighting mechanism of the lamp is considered to be due to the increase in the amount of heat at both ends of the lamp, especially in a hot cathode fluorescent lamp.

However, even when a thermocathode fluorescent lamp is used as a light source, it is necessary to secure luminance, brightness uniformity, life characteristics, and the like as a backlight device at or above the conventional backlight device.

In view of the above problems, the inventors of the present invention have examined the relationship between the number of lamps and the power capable of securing luminance, brightness uniformity, life characteristics, and the like in the case where a backlight device is constructed using a hot cathode fluorescent lamp as a light source.

The present invention has been made on the basis of such a background, and provides a desirable relationship between the number of thermal cathode fluorescent lamps and the respective power sources when a thermal cathode fluorescent lamp is used as a light source in a direct backlight device.

The direct type backlight device according to the present invention is a direct type backlight device which is disposed on the back of the liquid crystal panel having a diagonal size of the screen L inches, the ratio of the longitudinal length of the screen divided by the horizontal length r, a plurality of thermal cathodes A fluorescent lamp and a housing for accommodating the plurality of hot cathode fluorescent lamps, each of the hot cathode fluorescent lamps includes a bulb having a phosphor formed on an inner surface thereof, and a filament disposed in the bulb and emitting hot electrons; The direct type backlight device includes discharge stabilization means for stabilizing discharge of each of the thermal cathode fluorescent lamps, filament temperature control means for controlling the temperature of the filament in the respective thermal cathode fluorescent lamps to an appropriate value; Image luminance securing means for ensuring appropriate image luminance of the direct backlight, and the on-off of each of the thermal cathode fluorescent lamps; Includes a temperature increase controllable means for controlling the rising, the image luminance securing means and the temperature rise control means may be a number N of the heat cathode fluorescent lamp,

[1]

The discharge stabilization means and the filament temperature control means each have a power W (watt) of the thermal cathode fluorescent lamp,

[Number 2]

It is characterized by the fact that it is realized by satisfying the relationship.

In a preferred embodiment, the temperature increase controllable means functions as a heat dissipation device-free means capable of converging a temperature of each of the hot cathode fluorescent lamps to an appropriate value without using a heat dissipation device; The heat dissipator unnecessary means is the number N of the thermal cathode fluorescent lamp,

[Number 4]

It is characterized by the fact that it is realized by satisfying the relationship.

The direct type backlight device according to the present invention is a direct type backlight device which is disposed on the back of the liquid crystal panel having a screen size of approximately L inches and a ratio of the screen length divided by the length of the transverse direction r. A thermal cathode fluorescent lamp and a housing for accommodating the thermal cathode fluorescent lamp so that its longitudinal direction and the transverse direction coincide with each other, wherein the number N of the thermal cathode fluorescent lamps is

[1]

Each power W (watt) of the thermal cathode fluorescent lamp,

[Number 2]

It is characterized by satisfying the relational expression of.

In addition, the direct type backlight device according to the present invention is a direct type backlight device which is installed on the back of the liquid crystal panel whose diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length is r. A substantially straight column cathode fluorescent lamp, and a housing for accommodating the column cathode fluorescent lamp so that its longitudinal direction and the longitudinal direction coincide with each other, and the number N of the column cathode fluorescent lamps is

Number 5

The power W of each of the thermal cathode fluorescent lamps,

[Jos 6]

It is characterized by satisfying the relational expression of.

In addition, the direct type backlight device according to the present invention is a direct type backlight device which is installed on the back of the liquid crystal panel whose diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length is r. The light emitting part is folded, and the light emitting part includes M hot-light fluorescent lamps existing in a direction corresponding to the transverse direction in a region irradiating light to the liquid crystal panel, and a housing for accommodating the hot-cathode fluorescent lamps. The number N of thermal cathode fluorescent lamps is

[Jos 9]

Satisfies the above, and each power W of the thermal cathode fluorescent lamp is

[Jos 10]

It is characterized by satisfying the relational expression of.

In addition, the direct type backlight device according to the present invention is a direct type backlight device which is installed on the back of the liquid crystal panel whose diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length is r. The light emitting unit is folded, and the light emitting unit includes a thermal cathode fluorescent lamp that is present in the direction corresponding to the longitudinal direction in the region for irradiating light to the liquid crystal panel, and a housing for accommodating the thermal cathode fluorescent lamp, The power W of the thermal cathode fluorescent lamp,

[13]

Satisfies the number N of the thermal cathode fluorescent lamps,

[Jos 14]

It is characterized by satisfying the relational expression of.

A liquid crystal display according to the present invention is a liquid crystal display provided with the direct type backlight device.

According to the present invention, even when a thermocathode fluorescent lamp is used as a light source, it is possible to provide a backlight device capable of satisfactorily satisfying luminance, brightness uniformity and life characteristics.

In addition, in the direct type backlight device according to the second aspect of the present invention, each power W of the thermal cathode fluorescent lamp is

[Number 3]

It is characterized by satisfying the relational expression of.

In the direct type backlight device according to the third aspect of the present invention, each power W of the thermal cathode fluorescent lamp,

[Jos 7]

 It is characterized by satisfying the relationship.

In the direct type backlight device according to the fourth aspect of the present invention, each of the power W of the thermal cathode fluorescent lamp,

[Jos 11]

It is characterized by satisfying the relational expression of.

In the direct type backlight device according to the fifth aspect of the present invention, each power W of the thermal cathode fluorescent lamp,

[Joe 15]

It is characterized by satisfying the relational expression of.

According to the structure of these 2nd thru | or 5th side surface, even if the electrode with a narrow wire diameter was used, a long lifetime lifetime can be comprised.

Further, in the direct type backlight device according to the sixth aspect of the present invention, the number N of the thermal cathode fluorescent lamps is

[Number 4]

It is characterized by satisfying the relational expression of.

In the direct type backlight device according to the seventh aspect of the present invention, the number N of the thermal cathode fluorescent lamps is

[Wed 8]

It is characterized by satisfying the relational expression of.

In the direct type backlight device according to the eighth aspect of the present invention, the number N of the thermal cathode fluorescent lamps is

[Joe 12]

It is characterized by satisfying the relational expression of.

In the direct type backlight device according to the ninth aspect of the present invention, the number N of the thermal cathode fluorescent lamps is

[Joe 16]

It is characterized by satisfying the relational expression of.

According to the structures of the sixth to ninth aspects, it is possible to construct a backlight device in which age deterioration is suppressed even without using a special heat dissipation means.

In the direct type backlight device according to the embodiment of the present invention, the ratio r = 9/16, the number N is 0 <N <0.44L-1.22, and the power W is 0.4L + 1.3 <W <2.2L-25.7. Characterized by satisfying the relationship.

The direct type backlight device according to the embodiment of the present invention is characterized in that the ratio r = 9/16 and the power W satisfies a relation of 0.4L + 1.3 <W <1.1L + 0.2.

The direct type backlight device according to the embodiment of the present invention is characterized in that the ratio r = 9/16, and the number N satisfies a relational expression of 0.06L-0.01 <N <0.22L-0.61.

In addition, the direct type backlight device according to the embodiment of the present invention is characterized by satisfying a relational expression of L≥26.

According to this configuration, a liquid crystal display having a small number, low cost and good energy consumption efficiency can be realized, particularly in a large liquid crystal display having a 26-inch or larger type, compared with the case of using a conventional cold cathode fluorescent lamp.

1 is an exploded perspective view showing the configuration of a liquid crystal display 1 according to the embodiment.

2 is a graph of experimental results for defining the lower limit of the power W;

3 is a graph of experimental results for defining an upper limit of the power W;

4 (a) is a graph of experimental results for defining the lower limit of the number N of lamps. (b) is a graph which defines the lower limit of the number N of lamps.

5 (a) is a graph of experimental results for defining an upper limit of the number N of lamps. (b) is a graph which defines the upper limit of the number N of lamps.

Fig. 6 is a diagram showing the relationship between the shape of the lamp and the number N and the number M, respectively.

Fig. 7 is a diagram showing the relationship between the shape of the lamp and the number N and the number M, respectively.

8 is a diagram illustrating a schematic configuration of a direct backlight device.

9 is a plan view illustrating an effective screen of a liquid crystal panel.

10 is a diagram illustrating equations relating to general equation derivation.

11 is a table showing the relationship between the value of r and the power W and the number N;

FIG. 12 is a diagram illustrating the derived general formula, in which (a) is the lateral direction of the screen, and (b) is the case of the screen longitudinal direction.

FIG. 13 is a diagram illustrating the derived general formula, in which (a) shows the transverse direction of the screen of the bending lamp, and (b) shows the case of the screen longitudinal direction of the bending lamp.

(Explanation of the sign)

1 LCD Display 10 Backlight Unit

11 Thermal Cathode Fluorescent Lamps 14 Housing

20 LCD panel

The inventors of the present invention do not use a cold cathode fluorescent lamp (CCFL), which is the mainstream, which is suitable for a backlight for a liquid crystal display in which a large screen is gradually accelerating, and can input high output power per unit compared to a cold cathode fluorescent lamp. It has been researched and developed in consideration of moving to the one using a hot cathode fluorescent lamp (HCFL). As a result of diligent study by the inventor of the present invention during such development, the present inventors have found the preferable relationship between the number of thermo-cathode fluorescent lamps as light sources and the respective powers.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, for the sake of brevity, elements having substantially the same functions are denoted by the same reference numerals. In addition, this invention is not limited to a following example.

FIG. 1 is an exploded perspective view of the liquid crystal display 1 for explaining the configuration of the direct type backlight device 10 according to the embodiment of the present invention.

The liquid crystal display 1 shown in FIG. 1 has a liquid crystal panel 20 having a diagonal size of L inch and a ratio of the length of the screen divided by the length in the lateral direction r, and a direct backlight provided on the rear surface thereof. Device 10 is included.

The direct type backlight device 10 is composed of a plurality of thermal cathode fluorescent lamps 11 and a housing 14 accommodating the plurality of thermal cathode fluorescent lamps 11. Each hot cathode fluorescent lamp 11 is composed of a bulb having a phosphor formed on its inner surface, and a filament provided in the bulb to emit hot electrons.

According to the configuration of the present embodiment, the direct type backlight device 10 includes discharge stabilization means A for stabilizing the discharge of each of the thermal cathode fluorescent lamps 11 and the filament of each of the thermal cathode fluorescent lamps 11. Filament temperature control means (B) for controlling the temperature to an appropriate value, image luminance securing means (C) for securing the appropriate image brightness of the direct backlight 10, and the temperature rise of the thermal cathode fluorescent lamp 11, respectively. It is provided with a temperature rise controllable means (D) capable of controlling.

Here, the image luminance securing means (C) and the temperature rise controllable means (D) are the number N of the thermal cathode fluorescent lamps,

[1]

 It is realized by satisfying the relational expression of.

And the discharge stabilization means (A) and the filament temperature control means (B) is a power W (watt) of the thermal cathode fluorescent lamp 11, respectively,

[Number 2]

It is realized by satisfying the relational expression of.

In addition, the temperature increase controllable means (D) functions as a heat dissipation device-free means (E) capable of converging the temperature of each hot cathode fluorescent lamp 11 to an appropriate value without using a heat dissipation device.

And the image luminance securing means (C) and the radiator unnecessary means (E) is the number N of the thermal cathode fluorescent lamps,

[Number 4]

It is realized by satisfying the relational expression of.

The direct type backlight device 10 of the present embodiment includes discharge stabilization means (A) for stabilizing the discharge of each thermal cathode fluorescent lamp (11), filament temperature control means (B) for controlling the temperature of the filament to an appropriate value; Image luminance securing means (C) for ensuring appropriate image luminance and temperature rise controllable means (D) for controlling the temperature rise of each of the column cathode fluorescent lamps (11). This is realized by satisfying a predetermined relationship in the number of lamps 11 and the respective powers. Thus, for example, it is possible to secure an image brightness in which an image looks desirable without introducing a means such as an auxiliary light source such as an LED in addition to a thermocathode fluorescent lamp as a main light source. In addition, it is possible to operate the liquid crystal panel without the influence of temperature without introducing a means such as, for example, a sirocco fan for cooling from the back of the backlight.

In other words, in order to realize these means, it is necessary to provide an apparatus for fixing and driving an auxiliary light source, a sirocco fan, and the like. In this embodiment, the number and power of the lamps 11 and Since these means are realized by the relationship, the configuration of the backlight can be simplified, and the problem of cost increase can be avoided. Therefore, according to the structure of this embodiment, the direct type backlight device 10 provided with the thermo-cathode fluorescent lamp 11 which can present the image with favorable brightness, without abnormally operating a liquid crystal panel by heat generation can be implement | achieved. have.

Hereinafter, the technical meaning of each relational expression mentioned above and the detail of the Example which concerns on this invention are demonstrated, referring also another figure.

1. Configuration of direct backlight unit

1 is an exploded perspective view showing the configuration of a liquid crystal display 1 of the present embodiment.

The liquid crystal display 1 includes a liquid crystal panel 20 and a backlight device 10 provided on the rear surface of the liquid crystal panel.

The liquid crystal panel 20 has an effective screen size of, for example, 32 inches diagonally, and the effective screen 21 has an aspect ratio of 16: 9 (r ratio 9 divided by longitudinal length divided by horizontal length 9/16).

The backlight device 10 is a direct type, and includes a housing 14, a plurality of column cathode fluorescent lamps 11 (six in FIG. 1), a lighting circuit 12, and optical sheets 18. .

The housing 14 has an opening on the side of the liquid crystal panel 20, and the plurality of thermal cathode fluorescent lamps 11 are positioned in a horizontal direction of the screen (the longitudinal direction of the lamps 11 is parallel to the longitudinal direction of the screen). And at a predetermined interval in the horizontal direction of the screen. Moreover, in order to extract light to the liquid crystal panel 20 side of the housing 14, the board which surrounds the thermo-cathode fluorescent lamp 11 of the inner surface of the housing 14 in three surfaces is the reflecting plate 16 which has a light reflection characteristic. .

The dimension of the thermocathode fluorescent lamp (hereinafter may be referred to as "lamp") 11 is 12 mm for outer diameter of glass tube, 0.8 mm for thickness, and 730 mm for length for 32 inches. The gas enclosed in the glass tube is a mixed gas of Ar 50% and Kr 50%, for example, and the gas pressure is 600 Pa.

In addition, the dimensions of the lamp corresponding to other screen sizes are as follows.

45 inches Outer diameter of glass tube 12mm, thickness 0.8mm, length 1010mm

For 65-inch… Outside diameter of glass tube 25.5mm, thickness 0.8mm, length 1499mm

105 inches Outer diameter 38mm, thickness 0.9mm, length 2367mm of glass tube

The lighting circuit 12 is a power supply circuit for supplying power to the lamp 11, and has a dimming function for arbitrarily setting the amount of power to be supplied.

The optical sheets 18 are laminated with a thin plate having an optical action such as a diffusion plate, a diffusion sheet, a prism sheet, and a polarizing plate, and the surface of the optical sheets 18 serves as a light emitting surface of the backlight device. Silver uniformity of brightness is highly required.

2. Range of power W for screen size L

Next, the experiment which investigated the relationship between the lamp of the length corresponding to the screen size of a liquid crystal panel, and its power W (watt) is demonstrated.

(1) lower limit of power W

FIG. 2 is a diagram showing a graph of experimental results for defining a lower limit of power W. FIG. The horizontal axis of the graph is the screen size L (in inches), and the vertical axis is the power W of one lamp.

In this experiment, a thermal cathode fluorescent lamp having a length corresponding to the screen size when the lamp was placed in the transverse direction of the screen, such as 730 mm long for 32 inches and 1010 mm for 45 inches, was turned on to evaluate the discharge state. It did by doing.

This evaluation is unstable for a lamp whose power W is judged to be insufficient to generate or disappear a light streaks (hereinafter referred to as a moving streaks) that move in the glass tube in the longitudinal direction during discharge. ), And for the lamp which continues the discharge stably, it was judged as stable ("○" in the figure).

As shown in FIG. 2, it was found from the experimental results that the electric power W was stable in the region (not including the boundary) above the graph of the linear equation W = 0.4L + 1.3.

That is, the power W,

0.4L + 1.3 <W... (Equation 1)

The range satisfying the relational expression is preferable. By satisfying the relational expression of (Equation 1), discharge stabilization means A for stabilizing the discharge of each of the thermal cathode fluorescent lamps 11 is realized.

(2) upper limit of power W

3 is a diagram showing a graph of experimental results for defining an upper limit of the power W; The horizontal axis of the graph is the screen size L (in inches), and the vertical axis is the power W of one lamp.

This experiment lights up a thermo-cathode fluorescent lamp (32 inches outside diameter 12mm, 730mm length, 45mm outside diameter 18mm, length 1010mm) corresponding to the screen size, so that the lamp does not shorten its life. The upper limit of the power W was investigated.

When the power W input to the lamp is excessive, the emitter is rapidly consumed, reaching a lifespan in a short time, so that it cannot be used as a backlight.

The rate at which this emitter is consumed is determined by the electrode temperature, which is determined by the lamp current and the preheat current.

In the case where the lamp current is small, the electrode temperature can be maintained to the extent that the hot electron emission can be accelerated by the addition of the preheating current.

On the other hand, when the lamp current is too large, consumption of the emitter due to evaporation occurs even if the preheating current is zero. The electrode temperature at this time can be estimated from the ratio of hot resistance Rh to cold resistance Rc. If the Rh / Rc value is 6 or less, the electrode temperature is about 1000 ° C or less, and this range In this case, the emitter is not consumed to the extreme by evaporation.

The upper limit of the lamp power W whose Rh / Rc is 6 or less was investigated from the evaluation and simulation of the electrical characteristics of the lamp which lighted in this experiment.

As shown in FIG. 3, the power W is

W <2.2L-25.7... (Equation 2)

It turned out that it should just be in the range of. Therefore, the filament temperature control means B for suppressing the temperature of the filament in each of the hot cathode fluorescent lamps 11 to an appropriate value is realized by satisfying the relational expression of (Formula 2).

However, this range is limited to the case where a thick wire diameter (0.08 mm) electrode capable of flowing a lamp current of 0.8 A is used.

If the structure is to support the emitter using a thick wire diameter, the electrode body is large, making the optical design difficult. The range in the case of using the electrode which has sufficient support for an emitter support, and can be accommodated in the glass tube of about 20 mm of outer diameters became the following empirical formula.

W <1.1L + 0.2... (Equation 3)

That is, the filament temperature control means B is also realized by satisfying the relational expression of (Equation 3).

(3) synthesis of power W range

As described above, the relationship between the screen size L and the power W when the thermal cathode fluorescent lamp is arranged in the aspect ratio of the screen in the aspect ratio 16: 9,

0.4L + 1.3 <W <2.2L-25.7... (Equation 4)

More preferably,

0.4L + 1.3 <W <1.1L + 0.2... (Eq. 5)

I found it good to satisfy.

3. Range of Lamp Count N for Screen Size L

(1) Lower limit of the number of lamps N

Next, an experiment was conducted to investigate the lower limit of the optimal number of lamps N with respect to the screen size L.

The outline of the experiment is as follows.

First, a 32-inch backlight device was constructed using a lamp (outer diameter 12 mm, length 730 mm) corresponding to the 32 inch described above.

The number of lamps is different from 1, 2, 3, 4, 5, and the reflecting plate and the lamps are made to be as uniform as possible and the thickness of the light emitting surface of the backlight device is as uniform as possible depending on the number of lamps. The placement position is set.

Specifically, the distance between the lamp and the reflector is about 1 mm to 5 mm, and the distance between the lamp and the diffuser plate is about 5 mm to 33 mm.

Then, the liquid crystal panel is disposed on the light emitting surface side of the backlight device, and driven under conditions satisfying the power W (Equation 5) of the lamp to display still and moving images having various colors and gradations on the liquid crystal screen. The displayed screen was observed and evaluated by several evaluators including the inventors.

As a result, it was found that no matter how much the optical system is configured with one lamp, the screen is too dark, and even if it can be used in a dark place, a satisfactory image with sufficient contrast can be obtained in bright places, and at least two lamps are required. .

In addition, a backlight device having a screen size of 45 inches was configured by the lamp having the outer diameter of 18 mm and the length of 1010 mm, and the number of lamps was changed to 2, 3, 4, 6, and 8 lamps. In addition, it was confirmed that the difference between the outer diameter of 18mm and 12mm is a difference that does not affect the results.

The 45-inch case was evaluated as well, indicating that three or more lamps were needed.

The results of this experiment are shown in the graph of FIG. 4A. From this experiment, the number of lamps N is

0.06L-0.01 <N... (Equation 6)

It has been found that the range satisfying the above is good. Therefore, by satisfying the relational expression of this expression (6), the image luminance securing means (C) for securing the appropriate image luminance of the direct backlight 10 is realized. 4B shows a plot of values for a backlight device having a screen size of 65 inches on the graph of FIG. 4A.

(2) Upper limit of the number of lamps N

Next, an experiment was conducted to investigate the upper limit of the number N of lamps.

Since a hot cathode fluorescent lamp has a temperature 1.5 times to 2.0 times higher than that of a cold cathode fluorescent lamp, the problem of deterioration of the constituent members of the backlight device due to heat increases. When a 32-inch backlight device was configured to drive the power W of the lamp under the conditions satisfying Equation 5, the operation was performed without any problem when the temperature was six or less. In the case of seven or more, at least one of the problems such as discoloration of the reflecting plate at the bottom of the housing, warpage of the diffusion plate, and malfunction of the liquid crystal occurred. These problems can be reduced to some extent by blowing air in the backlight unit and making the reflecting plate at the bottom a member having a good heat dissipation (for example, a metal plate). In addition, when it became 14 or more, even if the heat dissipation means was improved, the aging deterioration by heat could not be suppressed.

On the other hand, 16 cold cathode fluorescent lamps have been used in the 32-inch backlight device and 24 cold cathode fluorescent lamps have been used in the 45-inch backlight device. Therefore, according to the configuration of the present embodiment, the number of lamps and the number of lighting circuits can be reduced to half or less. In addition, since two lighting circuits are required for driving a cold cathode fluorescent lamp in a 45-inch backlight device, the cost reduction effect is remarkable.

On the other hand, in the configuration of a 45-inch backlight device using a lamp having an outer diameter of 18 mm, no special heat dissipation means is required if it is 9 or less, and it has been found that the age or deterioration due to heat cannot be suppressed if it is 20 or more.

The results of this experiment are shown in the graph of FIG. 5A. From this experiment, the range of lamp number N is

 N <0.44L-1.22... (Eq. 7)

Is preferred. More preferably,

N <0.22L-0.61... (Eq. 8)

We found that it should be good.

Accordingly, by satisfying the relational expression of Expression (7), a temperature increase suppression means (D) capable of suppressing the temperature rise of each of the thermal cathode fluorescent lamps 11 is realized. In addition, by satisfying the relational expression of Equation (8), a heat dissipating device-free means (E) capable of converging the temperature of each hot cathode fluorescent lamp 11 to an appropriate value without using a heat dissipating device is realized.

5B shows a plot of values for a backlight device having a screen size of 65 inches on the graph of FIG. 5A.

(3) Total range of the number of lamps N

Based on the above experimental results and their considerations,

0 <N <0.44L-1.22... (Eq. 9)

On the back side, the screen on the liquid crystal panel can be seen in a dark place, and the backlight device can be constituted without adverse effects due to heat, provided that the heat dissipation means is appropriate.

0.06L-0.01 <N <0.22L-0.61... (Eq. 10)

In this case, a satisfactory image having a sufficiently high contrast even in bright places can be obtained, and a backlight device without deterioration can be constituted without using a special heat dissipation means. It is confirmed by verification that the number N in this range is applicable to 65 inches (outer diameter of lamp 25.5 mm, length 1499 mm) and 105 inches (outer diameter 38 mm of lamp, length 2367 mm).

4. Specific Example of Backlight Device Configuration

A specific example of the configuration of the started backlight device that satisfies the equations (4) and (10) will be described.

A 32-inch-sized backlight device was constructed using four hot cathode fluorescent lamps (outer diameter 12 mm and length 730 mm) in a transverse direction arrangement, and a power of 22 W was supplied per one.

In addition, six 45-inch-sized backlight devices were configured by using six hot cathode fluorescent lamps (18 mm in outer diameter and 1010 mm in length) in the horizontal direction arrangement, and 30W of power was supplied per one.

When combined with a liquid crystal panel, both backlight devices can obtain a satisfactory image that is sufficiently bright and have high contrast even in a bright place, and can be configured to have a backlight device that does not require special heat dissipation means and that does not deteriorate with age. I could confirm it.

5. Range of power W and number N when the lamp is arranged in the longitudinal direction of the screen

Up to now, the case in which the hot cathode fluorescent lamps are arranged in the substantially horizontal direction with respect to the screen has been described. However, the aspect ratio of the screen (9:16) (Equation 2), ( By applying to equation (3) or (equation 4), (expression 5),

0.23 (= 0.4 x 9/16) L + 1.3 <W <1.2 (= 2.2 x 9/16) L-25.7 = 0.23 L + 1.3 <W <1.2 L-25.7. (Eq. 11)

More preferred range is

0.23L + 1.3 <W <0.62L + 0.2... (Eq. 12)

Becomes

Regarding the number N, a new empirical equation was obtained based on (Equation 7) and (Equation 8).

0 <N <0.78L-3.43... (Eq. 13)

More preferably,

0.13L-0.04 <N <0.39L-1.71... (Eq. 14)

Becomes

6. Range when using a bend lamp

What has been described so far is a thermal cathode fluorescent lamp in which the light emitting part has a substantially linear shape, but the power W and the number of lamps M (number N No) can be defined.

6 and 7 are diagrams showing the relationship between the shape of the lamp and the number N and the number M, respectively.

As shown in Fig. 6A, the lamp includes a cylindrical bulb having a phosphor formed on its inner surface, and a pair of filaments provided at both ends of the bulb and emitting hot electrons.

In the case of a lamp in which the light emitting portion is folded, it can be defined as the number M of lamps existing in a linear direction in a region for irradiating light to the liquid crystal panel (hereinafter referred to as a "light irradiation region").

This light irradiation area may also be referred to as a light extraction area for taking out light from the backlight device. In addition, since the heat cathode fluorescent lamp emits light in the same manner except for the vicinity of the electrodes disposed at both ends, the light pole portions between the electrodes are used as light, and the light irradiation area is applied to the light pole portions of the lamp. It may also be referred to as a corresponding area.

The number of lamps present in the light irradiation area is equal to one lamp per lamp (Fig. 6 (a)) in the case where the lamp has a substantially linear shape.

On the other hand, in the case of a U-shaped lamp (Fig. 6 (b)), there are two lamps per lamp (M = 2N relationship). This is because one lamp is used, but two straight portions except for the U-shaped curvature portion are used as the light emitting portion.

The lamp shown in FIG. 6 (c) has a shape in which two glass tubes are bridged by bonding at a side far from the electrode, and the positive light column is U-shaped. Even in this case, two lamps exist in the linear direction by one lamp in the light irradiation area.

In the lamp shown in Fig. 7A, the positive wine column has an S shape. Also in this case, the same thought as in Fig. 6 (b) can be regarded as one or three lamps present in a linear direction.

In the lamp shown in Fig. 7B, the positive columner has an M shape (W shape). In this case, one lamp may be regarded as being present in one or four linear directions.

(1) When the screen is positioned horizontally

As described above, the relationship between the power W and the number M of lamps existing in the linearly transverse direction in the light irradiation area is about M. The length of the substantially straight portion of the dimming column is different in length, for example, the length of the non-light emitting portion such as a junction portion. Since it is larger than, it is derived similarly to (Equation 4) and (Equation 5),

0.4LM + 1.3 <W <2.2LM-25.7 (Eq. 15)

More preferably,

0.4LM + 1.3 <W <1.1LM + 0.2... (Eq. 16)

It is preferable to set it as the range of.

The relationship between the screen size L, the number N, and the number M is derived in the same manner as in the expressions (7) and (8).

N <(0.44L-1.22) / M... (Eq. 17)

More preferably,

(0.06L-0.01) / M <N <(0.22L-0.61) / M... (Eq. 18)

It is good to be in the range of.

(2) When the screen is positioned vertically

When there are M lamps in the longitudinal direction of the screen, a relational expression can be derived as in the horizontal direction of the screen, and the result is as follows.

0.23LM + 1.3 <W <1.2LM-25.7... (Eq. 19)

More preferably,

0.23 LM + 1.3 <W <0.62 LM + 0.2... (Eq. 20)

to be.

The relationship between the screen size L, the number N, and the number M is

0 <N <(0.78L-3.43) / M... (Eq. 21)

More preferably,

(0.13L-0.04) / M <N <(0.39L-1.71) / M (Equation 22)

to be.

7. About Thermo Cathode Fluorescent Lamp

In this embodiment, a hot cathode fluorescent lamp is used as a light source of a direct backlight device in place of a cold cathode fluorescent lamp generally used in the related art.

In a cold cathode fluorescent lamp, as the screen size increases, the starting voltage and the driving voltage become high, so that circuits and mechanical parts tend to be expensive. Thus, the present invention is particularly effective for large liquid crystal displays, for example, 26 inches or more.

In addition, the cold cathode fluorescent lamp needs a mechanism for maintaining insulation such as floating even when the cold cathode fluorescent lamp is driven on both sides at 40 inches. In addition, in a cold cathode fluorescent lamp, there is a power loss due to leakage current, which is approximately proportional to the length of the lamp.

In cold-cathode fluorescent lamps, the power loss rate for the screen size is almost constant. On the other hand, thermal cathode fluorescent lamps also require energy to maintain the electrode temperature, and power loss that does not contribute to light emission occurs. However, the power loss of the thermal cathode is constant regardless of the screen size (lamp length), and the power contributing to light emission is determined by the length of the positive column. With respect to the screen size, the power loss rate of the hot cathode fluorescent lamp is monotonous. If the screen size is small, the power loss rate due to leakage current of the cold cathode fluorescent lamp is equal to or less than the power loss rate due to electrode heating of the hot cathode fluorescent lamp. Will grow. From the above, if the screen size is 26 inches or more, by using the hot cathode fluorescent lamp, the driving voltage, which is about 1 kV in the cold cathode fluorescent lamp, can be driven at 100 V or less in the hot cathode fluorescent lamp, so that the power loss rate is lower than that of the cold cathode fluorescent lamp. Can reduce the cost of the circuit and the absence of the mechanism. Preferably, when the screen size is 40 inches or more, a backlight having a low power loss can be configured without requiring a mechanism for maintaining special insulation.

8. Generalization

In the above description, the relational expression is limited when the aspect ratio is 16: 9 (r = 9/16). However, a general formula can be derived by obtaining a correction coefficient based on r = 9/16. Hereinafter, the derivation of the general formula applicable even if the aspect ratio changes will be described.

(1) power W

a. When in landscape orientation

9 shows a screen whose size is L inches in the diagonal.

It is a figure which shows the formula concerning general formula derivation. 11 is a table showing the relationship between the value of r, the power W and the number N, and w = 3/4 in the table has the same meaning as the aspect ratio 4: 3.

12 is a diagram illustrating the derived general formula, in which (a) is the lateral direction of the screen and (b) is the longitudinal direction of the screen.

It is a figure which shows the derived general formula, (a) shows the transverse direction of the screen of a bending lamp, and (b) has shown the case of the longitudinal direction of the screen of a bending lamp.

First, the vertical direction of the screen is y, and the horizontal direction of the screen is x. Here, let r be the ratio of the length of the screen divided by the length of the transverse,

r = y / x... (Eq. 31)

Defined as

In addition, L is represented by (x) by x and y.

W = A × L + B (Eq. 32)

To,

W = A × a × L + B (Eq. 33)

And the correction coefficient a are given, and the correction coefficient a is obtained as in (Equation 42).

The equation (3) can be generalized by multiplying the correction coefficient a by the slope of the graph (Fig. 2) of the equation (3),

W <1.1aL + 0.2... (Eq. 34)

Becomes Similarly, by generalizing (Equation 4) and (Equation 5) and replacing the correction coefficient a with the ratio r, the general formulas of (Equation 4) and (Equation 5) are (Equation 52) and (Equation 53).

b. When in vertical orientation of the screen

Moreover, in the case of longitudinal arrangement, it is the same as the case of horizontal arrangement,

W = A × a × L + B (Eq. 34)

Wow,

A = A × b × L + B... (Eq. 35)

And correction coefficients a and b are given, and correction coefficients a and b are obtained as in (Equation 42) and (Equation 43). And the general formula of (equation 11) and (12) becomes (equation 62) and (formula 63).

(2) Number N

Similarly to the power W, the correction factor is obtained for the number N. In this case, since the required luminance (power) for obtaining the required brightness and the heat generated at the time of lighting are proportional to the square of the screen size L, the correction coefficient? Is obtained as shown in (Equation 44).

The correction coefficient λ is

λ = ab... (Eq. 36)

Has become a relationship.

a. When in landscape orientation

In the case of the horizontal arrangement, the equation (45) is used.

In these (equation 45), the variables of k and Q are arbitrary variables used for calculation. In (Eq. 45), a factor of minute values is formed by factoring, and a calculation is performed to remove the minute terms. From this equation, the general formula of the number N of lamps in the case of arranging the lamps in the lateral direction of the screen is the product calculated when r = 9/16. It is multiplied by the coefficient (b / a).

General formulas of (Formula 9) and (Formula 10) are as shown in (Formula 51) and (Formula 54), respectively.

b. When in vertical orientation of the screen

In the case of the longitudinal arrangement, (Formula 46) is assumed. From this equation, the first term is multiplied by the correction factor a, and the zero-order term is corrected for the formula calculated when r = 9/16 in the general formula of the number N of lamps when the lamps are arranged in the longitudinal direction of the screen. It is multiplied by the coefficient (a / b).

General formulas of (formula 13) and (formula 14) are as shown by (formula 61) and (formula 64), respectively.

(3) General formula when using a flexure lamp

a. When in landscape orientation

Similarly, generalization can be performed, and the general formulas corresponding to (Equation 15) and (Equation 16) are the results shown in (Equation 72) and (Equation 73), respectively.

Moreover, the general formula corresponding to (Equation 17) and (Equation 18) is a result shown by (Equation 71) and (Equation 74), respectively.

b. When in vertical orientation of the screen

Similarly, generalization can be carried out, and the general formulas corresponding to (Formula 19) and (Formula 20) are the results shown in (Formula 82) and (Formula 83), respectively.

Moreover, the general formula corresponding to (Equation 21) and (Equation 22) is a result shown by (Equation 81) and (Equation 84), respectively.

According to the direct type backlight device according to the present invention, it is possible to provide a backlight device useful in practice by converging the power W, the number N, and the like into a predetermined range.

Claims (19)

A direct type backlight device which is disposed on the back of the liquid crystal panel having a diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length r. A plurality of thermal cathode fluorescent lamps, A housing accommodating the plurality of thermal cathode fluorescent lamps, Each of the thermal cathode fluorescent lamps includes a bulb having a phosphor formed on an inner surface thereof, and a filament installed in the bulb and emitting hot electrons. The direct type backlight device, Discharge stabilization means for stabilizing discharge of each of the thermal cathode fluorescent lamps; Filament temperature control means for controlling the temperature of the filament in each of the hot cathode fluorescent lamps to an appropriate value; Image luminance securing means for securing appropriate image luminance of the direct backlight; Temperature rise controllable means for controlling a temperature rise of each of the thermal cathode fluorescent lamps; The image luminance ensuring means and the temperature increase control means, The number N of the thermal cathode fluorescent lamps, [1]

Is satisfied by satisfying the relationship The discharge stabilization means and the filament temperature control means, The power W (watt) of each of the thermal cathode fluorescent lamps, [Number 2]

The direct type backlight, which is realized by satisfying the relationship. The method of claim 1, The temperature increase controllable means functions as a heat dissipation device-free means capable of converging the temperature of each thermal cathode fluorescent lamp to an appropriate value without using a heat dissipation device. The image luminance ensuring means and the heat dissipation device unnecessary means, The number N of the thermal cathode fluorescent lamps, [Number 4]

The direct type backlight, which is realized by satisfying the relationship. A direct type backlight device which is disposed on the back of the liquid crystal panel having a diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length r. A thermal cathode fluorescent lamp in which the light emitting portion is approximately straight, A housing for accommodating the thermal cathode fluorescent lamp so that its longitudinal direction and the transverse direction coincide; The number N of the thermal cathode fluorescent lamps, [1]

 Each power W (watt) of the thermal cathode fluorescent lamp, [Number 2]

The direct type backlight device, characterized in that to satisfy the relation. The method of claim 3, wherein The ratio r = 9/16, The number N is 0 <N <0.44L-1.22, The power W is 0.4L + 1.3 <W <2.2L-25.7 The direct type backlight device, characterized in that to satisfy the relation. The method of claim 3, wherein The power W of each of the thermal cathode fluorescent lamps, [Number 3]

The direct type backlight device, characterized in that to satisfy the relation. The method of claim 5, wherein The ratio r = 9/16, The power W is 0.4L + 1.3 <W <1.1L + 0.2 The direct type backlight device, characterized in that to satisfy the relation. The method according to claim 3 or 5, The number N of the thermal cathode fluorescent lamps, [Number 4]

 The direct type backlight device, characterized in that to satisfy the relation. The method of claim 7, wherein The ratio r = 9/16, The number N is 0.06L-0.01 <N <0.22L-0.61 The direct type backlight device, characterized in that to satisfy the relation. A direct type backlight device which is installed on the back of the liquid crystal panel whose diagonal size of the screen is L inches and the ratio of the longitudinal length of the screen divided by the horizontal length is r. A thermal cathode fluorescent lamp in which the light emitting portion is approximately straight, And a housing accommodating the thermal cathode fluorescent lamp so that its longitudinal direction and the longitudinal direction coincide. The number N of the thermal cathode fluorescent lamps, Number 5

 The power W of each of the thermal cathode fluorescent lamps, [Jos 6]

The direct type backlight device, characterized in that to satisfy the relation. The method of claim 9, The power W of each of the thermal cathode fluorescent lamps,  [Jos 7]

The direct type backlight device, characterized in that to satisfy the relation. The method according to claim 9 or 10, The number N of the thermal cathode fluorescent lamps, [Wed 8]

The direct type backlight device, characterized in that to satisfy the relation. A direct type backlight device which is disposed on the back of the liquid crystal panel having a diagonal size of the screen is L inches, and the ratio of the longitudinal length of the screen divided by the horizontal length r. A heat cathode fluorescent lamp in which light emitting parts are folded, and the light emitting parts are present in an amount corresponding to M in the direction corresponding to the transverse direction in a region irradiating light to the liquid crystal panel; A housing for accommodating the thermal cathode fluorescent lamp, The number N of the thermal cathode fluorescent lamps, [Jos 9]

Satisfying The power W of each of the thermal cathode fluorescent lamps, [Jos 10]

The direct type backlight device, characterized in that to satisfy the relation. The method of claim 12, The power W of each of the thermal cathode fluorescent lamps, [Jos 11]

The direct type backlight device, characterized in that to satisfy the relation. The method according to claim 12 or 13, The number N of the thermal cathode fluorescent lamps, [Joe 12]

The direct type backlight device, characterized in that to satisfy the relation. A direct type backlight device which is installed on the back of the liquid crystal panel whose diagonal size of the screen is L inches and the ratio of the longitudinal length of the screen divided by the horizontal length is r. A heat cathode fluorescent lamp in which a light emitting portion is folded, and wherein the light emitting portion is present in an area corresponding to the longitudinal direction in an area in which light is radiated to the liquid crystal panel; A housing for accommodating the thermal cathode fluorescent lamp, The power W of the thermal cathode fluorescent lamp, [13]

Satisfying The number N of each of the thermal cathode fluorescent lamps, [Jos 14]

The direct type backlight device, characterized in that to satisfy the relation. The method of claim 15, The power W of each of the thermal cathode fluorescent lamps, [Joe 15]

The direct type backlight device, characterized in that to satisfy the relation. The method according to claim 15 or 16, The number N of the thermal cathode fluorescent lamps, [Joe 16]

The direct type backlight device, characterized in that to satisfy the relation. The method according to any one of claims 1 to 17, A direct type backlight device, characterized by satisfying a relationship of L≥26. The direct type | mold backlight device of any one of Claims 1-18 is provided, The liquid crystal display characterized by the above-mentioned.

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