JP2001022285A - Back light device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress periodical irregularity of brightness on the light emitting face while keeping the high availability of light flux with only by the basic configuration of a just-under back light device. SOLUTION: In the just-under back light device, the arrangement interval L of fluorescent tubes 4, the distance d between the center axis of the fluorescent tube 4 and a diffusion plate 2, and the transmittance α of the diffusion plate 2 for all rays are determined in such a manner that (d) and L are in the relation of 0.5<=d/L<0.8 and that in the coordinate plane with d/L as abscissa and α as ordinate, the coordinate (d/L, α) is present in the region defined by lines connecting the coordinates A(0.5, 0.6), B(0.8, 0.8), C(0.8, 0.38) and D(0.5, 0.35).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for irradiating a liquid crystal display unit of a liquid crystal display device from behind, and more particularly, to a structure of a direct type backlight device having high luminance and high luminance uniformity.

[0002]

2. Description of the Related Art Conventionally, as a backlight device for a liquid crystal display, a device using a fluorescent tube as a light source has been widely used, and a system called an edge light type has been mainly used. As shown in FIG. 6, the edge light type has a configuration in which a thin fluorescent tube 1 is arranged at an end of a light guide plate 9, and although there is a limit to a high luminance of a light emitting surface, it is easy to reduce the thickness of the light emitting surface. High luminance uniformity is obtained on the light emitting surface of the light plate 9.

However, the application field of the liquid crystal display is
The field of display has been expanded from the field of conventional monitors for personal computers and portable electronic devices to the field of video display such as television receivers, and there is a demand for a backlight device having a much higher brightness than before.

[0004] In recent years, in response to such a demand for higher luminance, a system called a direct type has been increasingly used. As shown in FIG. 7A, the direct-type backlight device has a configuration in which a plurality of fluorescent tubes 4 arranged in parallel, a reflecting plate 3 provided on the back surface, and a diffusing plate 2 forming a light emitting surface are combined. Become. In contrast to the edge light type, the effective use efficiency of the luminous flux radiated from the fluorescent tube 4 (the ratio of the luminous flux radiated from the light emitting surface to the luminous flux radiated from the lamp) is as high as about 0.7 and the number of lamps used Can be increased, so that the light emitting surface can be easily increased in luminance.

However, the direct type backlight device has a problem that the luminance uniformity of the light emitting surface is poor because the following two types of luminance unevenness occur. The first luminance unevenness is shown in FIG.
As shown in (b), periodic luminance unevenness occurs due to an increase in luminance immediately above the fluorescent tube 1, and the second luminance unevenness is in both end regions of the light emitting surface where the fluorescent tubes 1 arranged in parallel end. Reference numeral 5 denotes uneven brightness at both ends caused by darkening compared to the central area.

[0006] When the luminance uniformity of the light emitting surface of the backlight device is low, display unevenness occurs on the display screen of the liquid crystal display. With the recent improvement in image quality of liquid crystal displays,
The backlight device is also required to have a high luminance uniformity. For example, according to the present inventors' evaluation at a visual angle of 10 ° using a liquid crystal display, the luminance uniformity is 0.1 mm.
It needs to be 95 or more. The luminance uniformity is luminance (amount of light flux emitted at a unit solid angle in a certain direction).
Is a numerical value obtained by dividing the minimum value in the distribution within the light emitting surface by the maximum value, and corresponds to the ratio of light and dark when the light emitting surface is observed from a certain direction.

Conventionally, various measures have been taken to improve the luminance uniformity. First, with regard to the periodic luminance unevenness, there is a cause of high luminance in the vicinity of the fluorescent tubes arranged in parallel. Therefore, it is possible to reduce the luminance unevenness by keeping the diffusion plate, which is the light emitting surface, away from the fluorescent tube 1. You can,
The backlight device becomes thicker. Therefore, it has been studied to improve the luminance uniformity by optimizing the relationship between the arrangement interval of the fluorescent tubes and the thickness of the backlight device. It is described that the thickness of the lamp space is limited to a predetermined range. However, the luminance uniformity obtained by such optimization was about 0.85, which was not sufficient.

For this reason, various methods have been proposed for suppressing periodic luminance unevenness by using an optical element for uniformizing luminance. Among them, (a) a method of diffusing a zebra-like light amount correction pattern called a light screen is proposed. A method of printing on a plate or the like to reduce the luminous flux radiated directly above the fluorescent tube, or (b) using a corrugated reflector, the reflected light from the reflector is equivalent to the middle of the fluorescent tube and the fluorescent tube The method of focusing on an area to be focused is mainly adopted.

[0009] As a means for solving the uneven brightness at both ends, light is mainly concentrated on both end regions 5 where the brightness is reduced by providing inclined surfaces 3 a inclined at a predetermined angle at both ends of the reflector 3. Means for reflecting light are employed.

[0010]

However, when a light screen is used as a means for solving the periodic luminance unevenness, since a part of the light beam is blocked, the effective utilization rate of the light beam emitted from the fluorescent tube is reduced. There is a problem that the brightness is lowered and sufficient luminance cannot be obtained. (B) In the case where the corrugated reflector is used, there is a problem that the configuration of the device becomes complicated and the manufacturing cost of the backlight device increases.

Further, as a means for solving the uneven brightness at both ends, when the inclined surface 3a is provided on the reflector, there is a problem that complicated design and trial production are required for adjusting the inclination angle.

Accordingly, the present invention is directed to a direct-type backlight device capable of realizing high luminance uniformity by suppressing periodic luminance unevenness of a light-emitting surface while maintaining a high effective light flux utilization rate only by the basic configuration of a direct-type backlight device. A first object is to provide a mold backlight device.

It is a second object of the present invention to provide a direct-type backlight device capable of suppressing luminance unevenness at both ends with a simple configuration that does not require complicated design and trial production.

[0014]

In order to achieve the first object, according to the first aspect of the present invention, a plurality of linear light sources arranged in parallel and light from the light sources are provided. A direct-type backlight device including a reflecting plate that reflects light, and a diffuser plate that diffuses and irradiates the direct light from the light source and the reflected light from the reflecting plate, wherein an arrangement interval of the light sources is L, and Assuming that the distance between the central axis and the diffusion plate is d, and the total light transmittance of the diffusion plate is α, (a) 0.5 ≦ d /
L <0.8, (b) In a coordinate plane where the horizontal axis is d / L and the vertical axis is α, the coordinate (d / L, α) is the coordinate A
(0.5, 0.6), coordinate B (0.8, 0.8), coordinate C (0.8, 0.38) and coordinate D (0.5, 0.3)
It is characterized by being in an area surrounded by a line connecting 5).

Further, according to the present invention, a plurality of linear light sources arranged in parallel, a reflecting plate for reflecting light from the light source, a direct light from the light source and a light from the reflecting plate. A direct-type backlight device including a diffusion plate for diffusing and irradiating reflected light, wherein L is an arrangement interval of the light sources, and d is a distance between a central axis of the light source and the diffusion plate.
/L≧0.8 is a direct type backlight device.

In order to achieve the second object,
According to a third aspect of the present invention, there are provided a plurality of linear light sources arranged in parallel, a reflector for reflecting light from the light source, direct light from the light source and reflected light from the reflector. A direct-type backlight device including a diffusion plate that diffuses and irradiates a light source, wherein a reflection surface perpendicular to an arrangement direction of the light sources is provided on both outer sides of the light sources arranged in parallel, and The distance from the center axis is set to 1 / the distance of the arrangement of the light sources.
2 is characterized.

Further, the invention according to claim 4 is characterized in that the reflection surface is formed by vertically bending both ends of the reflection plate.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) In this embodiment, the periodic luminance of the light emitting surface is maintained by using only the fluorescent tube, the plane reflector, and the diffuser, which are the basic components of the direct-type backlight device, while maintaining a high effective light flux utilization rate. An object of the present invention is to provide a direct backlight device capable of suppressing unevenness. 1A and 1B are a plan view and a cross-sectional view illustrating a direct-type backlight device according to the present embodiment. The housing 1 of the direct type backlight device includes:
The plane reflection plate 3 and the diffusion plate 5 are assembled in a box shape. Case 1
, Fluorescent tubes 4 as linear light sources are arranged in parallel at a constant interval L. The reflecting plate 3 is a metal plate or a resin plate having a high light reflectivity or a plate coated with a white paint or a white resin sheet having a higher light reflectivity. Reflects light from
The diffusion plate 5 is made of a white resin material such as acrylic or the like,
It is located at the front of the fluorescent tube 4 and irradiates the direct light from the fluorescent tube 4 and the reflected light from the reflector 3 in a forward direction.

In such a direct type backlight device, the present inventors have proposed an arrangement interval L of the fluorescent tubes 1, a distance d between the central axis of the fluorescent tubes 1 and the diffusion plate 2, and a total light transmittance α of the diffusion plate 2.
It has been found that, by giving a predetermined relationship between, the periodic luminance unevenness can be suppressed and a high luminance uniformity of 0.95 or more can be realized while maintaining a high light flux utilization rate of 0.7 or more. In this embodiment, the luminance uniformity refers to the luminance uniformity in the central region of the backlight device, and does not include the influence of luminance unevenness at both ends.

Hereinafter, three parameters such as the arrangement interval L of the fluorescent tubes 1, the distance d between the central axis of the fluorescent tubes 1 and the diffusion plate 2, and the total light transmittance α of the diffusion plate, the effective light flux utilization rate and the luminance The result of examining the relationship with the uniformity will be described in detail.

First, the dependence of the incident light beam uniformity on the inner surface of the diffusion plate 2 with respect to the d / L value was examined, and the result was as shown in FIG. The incident light beam uniformity is a numerical value obtained by dividing the minimum value in the in-plane distribution of the light beam amount incident on the inner surface of the diffusion plate 2 by the maximum value, and indicates the uniformity of the illuminance. The brightness uniformity and the incident light beam uniformity have a fixed relationship, and the brightness uniformity increases when the incident light beam uniformity is high and the divergent direction of the output light beam is uniform. That is, the brightness uniformity is 0.9
In order to increase it to 5 or more, the incident light flux uniformity needs to be at least 0.95 or more.

The graph of FIG. 2 was measured experimentally. In the measurement, the light emitting surface size of the casing 1 of the backlight device was 400 mm × 300 mm, and the center axis of the fluorescent tube 4 and the inside of the diffusion plate 2 were measured. The distance d from the surface is 15mm ~ 3
0 mm, and the fluorescent tube 4 has a tube diameter of 3 mm and a tube current of 7 mA.
The cold cathode fluorescent tube in operation was used, and a stainless steel plate coated with a white resin sheet having a diffuse reflectance of 95% was used as the reflection plate 3. The dependency of the incident light beam uniformity on the d / L value is determined by scanning the micro light receiving element and measuring the distribution of the incident light beam while changing the depth size of the housing 1 and the arrangement size of the fluorescent tube 4. Was.

As can be seen from FIG. 2, the incident light flux uniformity is determined by the ratio (= d / L value) of the distance d between the central axis of the fluorescent tube 4 and the inner surface of the diffusion plate 2 to the arrangement interval L of the fluorescent tubes 4. Depends almost exclusively on For example, if the d / L values are the same, the distance f between the central axis of the fluorescent tube 4 and the reflector 3 is 2 mm to 6 m.
Even if it is changed in the range of m, the incident light beam uniformity does not change much. Further, the incident light beam uniformity sharply increases at the beginning as the d / L value increases, reaches 0.95 at d / L = 0.5, and thereafter, the rate of increase slows down and d / L =
It reaches almost 1.0 at 0.80.

Therefore, in order to realize a direct-type backlight device having a luminance uniformity of 0.95 or more, the d / L value needs to be at least 0.50 or more, and more preferably 0.80 or more. It turns out that it is preferable.

Next, in the backlight device having the configuration shown in FIG. 1 designed by changing the d / L value in the range of 0.50 to 1.20, the luminance is adjusted while appropriately changing the total light transmittance α of the diffusion plate 2. The uniformity and luminous flux effective utilization were measured. The total light transmittance α of the diffusion plate and the light diffusivity have a fixed relationship, and the light diffusivity decreases as the total light transmittance α increases.

In the measurement, the distance f between the central axis of the fluorescent tube 4 and the reflector 3 is fixed at 3 mm, and d is 15 mm to 30 mm.
It was selected within the range. The luminance uniformity is calculated from the luminance distribution on the surface of the diffusion plate 2 measured by a luminance meter, and the luminous flux effective utilization efficiency is calculated based on the luminance value of the diffusion plate surface 2 and the amount of radiant luminous flux on the light emitting surface obtained from the orientation distribution thereof. 4 and was calculated by dividing by the amount of emitted light flux.

First, the total light transmittance α is set to 1 by using a transparent acrylic resin plate for the diffusion plate 2, and the uniformity of the luminous flux incident on the diffusion plate 2 and the luminance uniformity on the outer surface (= light emitting surface) of the diffusion plate 2. When the relationship between the degrees was examined, the two values were almost linear, but the absolute values of the two did not match, and the brightness uniformity showed a value 0.05 to 0.10 lower than the incident light flux uniformity. Was.
From this, it was confirmed that the luminance uniformity depends not only on the incident light flux uniformity on the diffusion plate 2 but also on the uniformity of the light flux diverging direction. Therefore, in order to improve the brightness uniformity, it is necessary to reduce the total light transmittance α to increase the light diffusion rate, thereby improving the uniformity of the luminous flux diverging direction. If it is too long, the luminous flux effective utilization rate becomes insufficient.

Therefore, for various d / L values, the total light transmittance α satisfying both the luminance uniformity and the effective luminous flux utilization factor.
FIG. 3 shows the results of examining the range of. As can be seen from FIG. 3, the higher the α, the lower the luminance uniformity, but the larger the d / L value, the higher the limit value of α at which the luminance uniformity is 0.95 or more. On the other hand, the lower the α is, the lower the luminous flux effective utilization rate is, but the limit value of α at which the luminous flux effective utilization rate becomes 0.7 or more hardly changes depending on the d / L value. That is, the range of the total light transmittance α that satisfies the luminance uniformity of 0.95 or more and the effective luminous flux of 0.7 or more tends to be wider as the d / L value is larger. Although the measured values are not shown in FIG. 3, d / L ≧
In the range of 0.8 (the range in which the incident light flux uniformity reaches 1.0 in FIG. 2), both the brightness uniformity and the effective light flux utilization can be satisfied in a wide range of the total light transmittance α. It can be said that a backlight device having high luminance and high luminance uniformity can be realized very easily. For example, d / L =
In the case of a backlight device with 0.8, a translucent white acrylic plate is used for the diffusion plate 2 (total light transmittance α = 0.
80) Even when the luminous flux effective utilization efficiency was increased to 0.81, the target value of 0.95 was secured as the luminance uniformity. However, even if it is said that the larger the d / L value is, the more advantageous it is, the brightness uniformity reaches almost 1.0 when d / L = 1.2. No advantageous effect can be obtained.

On the other hand, it is advantageous that the d / L value is small in order to reduce the thickness of the backlight device, and it is desirable that the d / L value be smaller than 0.8 when emphasizing the reduction in thickness. Therefore, in the range of 0.5 ≦ d / L <0.8,
FIG. 4 shows the range of the total light transmittance α that satisfies both the luminance uniformity and the effective luminous flux. FIG.
The coordinate plane is shown with the horizontal axis being d / L and the vertical axis being α,
Coordinate A (0.5, 0.6), coordinate B (0.8, 0.
8), coordinate C (0.8, 0.38) and coordinate D (0.
5, 0.35) is a range that satisfies both the reference values of the luminance uniformity and the luminous flux effective utilization rate. That is, 0.5 ≦ d / L <
In a thin backlight device satisfying 0.8, a direct-type backlight device having high luminance and high luminance uniformity can be obtained only by combining the diffusion plate 2 having the total light transmittance α satisfying the range shown in FIG. be able to.

Note that, in addition to the basic structure of the direct-type backlight device shown in FIG. 1, an additional diffusion sheet, light-collecting sheet, polarization conversion sheet, or the like may be superimposed. The transmittance α is a value obtained by superposing a diffusion plate and these sheets. Further, in the case of a configuration in which the total light transmittance α differs depending on the position of the diffusion plate, it has been confirmed by an experiment that the average value of the area of the diffusion plate may be obtained.

(Embodiment 2) The present embodiment provides a direct-type backlight device capable of suppressing luminance unevenness at both ends with a simple configuration requiring no complicated design and trial production. FIG. 5 is a cross-sectional view illustrating the backlight device according to the present embodiment. In FIG. 5, reference numeral 1 denotes a housing of the backlight device, 2 denotes a diffusion plate, 3 denotes a reflection plate, and 4 denotes a fluorescent tube which is a linear light source. At both outer sides of the fluorescent tubes 4 arranged in parallel at a constant interval L, both end portions 3a of the reflecting plate 3
Are vertically folded to form a reflecting surface 3a perpendicular to the arrangement direction of the fluorescent tubes 4.

The reflecting surface 3a functions as a mirror surface, and the fluorescent tube 4
A virtual image 7 of the fluorescent tube is created at a position where the mirror image is symmetric. Therefore, by setting the distance between the central axis of the outermost fluorescent tube 4 and the reflection surface 3a to be の of the arrangement interval L of the fluorescent tubes,
The same effect can be obtained as if the fluorescent tubes 4 were arranged outside the housing 1 at a constant interval L. Therefore, with such a configuration, it is possible to suppress a decrease in the brightness of both end regions 5 of the backlight device and improve the brightness uniformity. Here, an example is shown in which the reflecting surface 3a is formed by folding both end portions of the reflecting plate 3 vertically, but the reflecting surface may be provided by a member independent of the reflecting plate 3.

[0033]

The present invention has the following effects because it is configured as described above. According to the first aspect of the present invention, in the basic configuration of the direct type backlight device, (a) 0.5 ≦ d / L <0.8, (b) the horizontal axis is d / L, and the vertical axis is d / L. In a coordinate plane where the axis is α, the coordinates (d
/ L, α) are coordinates A (0.5, 0.6) and coordinates B
(0.8, 0.8), d, L, and d are within an area surrounded by a segment connecting the coordinates C (0.8, 0.38) and the coordinates D (0.5, 0.35). Since α is set, it is possible to provide a backlight device with high luminance, thinness and high luminance uniformity only by its basic configuration.

According to a second aspect of the present invention, the distance between the arrangement of the light sources is L, the distance between the central axis of the light source and the diffusion plate is d, and d / L ≧ 0.8. A backlight device with high luminance and high luminance uniformity can be provided.

According to a third aspect of the present invention, in the direct-type backlight device, vertical reflecting surfaces are provided at predetermined positions on both outer sides of the light sources arranged in parallel. It is possible to provide a backlight device that suppresses a decrease in luminance of a region and has high luminance uniformity.

Further, in the invention according to the fourth aspect, since the reflecting surface is formed by bending both ends of the reflecting plate of the backlight device vertically, the brightness of both end regions of the backlight device can be reduced with a simpler configuration. Can be suppressed.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a cross-sectional view illustrating a direct-type backlight device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an incident light beam uniformity on an inner surface of a diffusion plate and a d / L value.

FIG. 3 is a graph showing a relationship between a luminance uniformity and a light flux effective use efficiency of a light emitting surface, and a total light transmittance α of a diffusion plate.

FIG. 4 is a graph showing ranges of d / L values and α values satisfying a luminance uniformity of 0.95 or more and a luminous flux effective use efficiency of 0.70 or more.

FIG. 5 is a sectional view showing a direct-type backlight device according to Embodiment 2 of the present invention.

FIG. 6 is a perspective view showing a basic configuration of a conventional edge light type backlight device.

FIG. 7A is a perspective view showing a basic configuration of a conventional direct-type backlight device, and FIG. 7B is a graph showing a luminance distribution in a central area of a light emitting surface.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Backlight device housing 2 Diffusing plate 3 Reflecting plate 3 a End of reflecting plate (reflecting surface) 4 Fluorescent tube 7 Virtual image of fluorescent tube 9 Light guide plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Machitori Watari 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Hiroshi Iwata 2-9-95 Nagara Higashi, Kita-ku, Osaka-shi, Osaka West Inside Electric Co., Ltd. (72) Inventor Daishi Uehara 2-9-1-9 Nagaraga Higashi, Kita-ku, Osaka-shi, Osaka West F Co., Ltd. F-term (reference) 2H091 FA14Z FA31Z FA42Z FD03 LA03 LA18 5G435 AA01 BB03 FF03 FF06 GG26

Claims (4)

[Claims] 1. A plurality of linear light sources arranged in parallel, a reflector located on the back of the light source to reflect light from the light source, and a direct light from the light source located on the front of the light source A direct-type backlight device including a diffusion plate that diffuses and irradiates light and reflected light from the reflection plate, wherein an arrangement interval of the light sources is L, and a distance between a central axis of the light source and the diffusion plate is d. (A) 0.5 ≦ d / L <0.8, where α is the total light transmittance of the diffusion plate;
(B) In a coordinate plane where the horizontal axis is d / L and the vertical axis is α, the coordinates (d / L, α) are coordinates A (0.5, 0.
6), coordinates B (0.8, 0.8), coordinates C (0.8,
0.38) and the area surrounded by the line connecting the coordinates D (0.5, 0.35). 2. A plurality of linear light sources arranged in parallel, a reflector located on the back of the light source to reflect light from the light source, and a direct light from the light source located on the front of the light source. A direct-type backlight device including a diffusion plate that diffuses and irradiates light and reflected light from the reflection plate, wherein an arrangement interval of the light sources is L, and a distance between a central axis of the light source and the diffusion plate is d. , D / L ≧ 0.8, a direct type backlight device. 3. A plurality of linear light sources arranged in parallel, a reflector located on the back of the light source to reflect light from the light source, and a direct light from the light source located on the front of the light source. A direct-type backlight device including a diffusion plate that diffuses and irradiates light and reflected light from the reflection plate, wherein a reflection surface perpendicular to an arrangement direction of the light sources is provided on both outer sides of the light sources arranged in parallel. A direct-type backlight device, wherein a distance between a central axis of a light source adjacent to the reflection surface and the reflection surface is set to 1/2 of an arrangement interval of the light sources. 4. The direct-type backlight device according to claim 3, wherein the reflection surface is formed by vertically bending both ends of the reflection plate.