JP4305735B2 - Backlight unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a backlight unit that is arranged on the back surface of a transmissive liquid crystal panel to illuminate, and more specifically, between a reflector and a light transmissive diffuser facing each other in parallel, The present invention relates to an improvement in reflection characteristics on the reflector side in a configuration in which a plurality of straight tube fluorescent lamps are arranged.
[0002]
[Prior art]
As is well known, a transmissive liquid crystal panel needs to be provided with a strong light source on the back surface, and a backlight unit that can obtain surface light emission in a thin flat shape is disposed on the back light source.
[0003]
This type of backlight unit often uses a long straight tube type fluorescent lamp as a light source. Structurally, the backlight unit has a side light type in which a fluorescent lamp is arranged at the periphery of the light emitting surface, or a thin flat body. There is a direct type that obtains diffused light by arranging a plurality of fluorescent lamps.
[0004]
The direct-type backlight unit will be described with reference to the typical configuration example according to the present invention shown in FIG. 4, but the main body 1 has a shallow dish shape with a peripheral edge raised, and a plurality of fluorescent lamps 2 are arranged inside. A light transmissive diffusion plate 3 is attached to the opening. As shown in FIG. 1, the inner surface of the main body 1 is a reflecting plate 5 (the same material as the diffuse reflecting portion 11 in the embodiment of the present invention) that mainly performs diffuse reflection, and diffuses the light of the fluorescent lamp 2. It diffuses with the plate 3 to obtain surface emission. This direct type is preferred because it has higher light utilization efficiency than the side light type and has an advantage in high luminance display.
[0005]
In recent years, display devices using liquid crystal panels have been increased in screen size. For this reason, the backlight unit is required to have a large screen size due to the demands of such mounting devices, and has been reduced in thickness to save space. It has been demanded.
[0006]
However, in the direct type backlight unit, since the fluorescent lamp 2 and the diffusion plate 3 approach each other when the thickness is reduced, there is a problem that the light distribution becomes non-uniform and the luminance on the diffusion plate 3 is uneven. As shown in FIG. 2, the light from the diffusion plate 3 includes direct light from the fluorescent lamp 2 and reflected light from the reflection plate 5, and a combination of these is light distribution. Since the reflection at the reflector 5 is a so-called scattered reflection, the reflected light follows Lambert's cosine law. That is, the reflected light from an appropriate position A on the reflecting plate 5 changes gently in proportion to the cosine of the angle θ formed with the normal of the reflecting surface, which diffuses the light intensity distribution on the diffusing plate 3. There is an averaging effect. However, the light is directly concentrated at the position facing the fluorescent lamp 2, and as a result, the light distribution falls at the intermediate point B of the arrangement pitch P of the fluorescent lamp 2, and the luminance distribution becomes uneven.
[0007]
For example, FIG. 3 is a graph showing the luminance distribution for the conventional example of FIG. 1, and this luminance distribution characteristic is obtained by simulation. The horizontal axis corresponds to the array of fluorescent lamps 2 shown in FIG. The center position and the left end of the backlight unit correspond to one side end of the backlight unit. The vertical axis represents the luminance [cd / m ² ] on the diffusion plate 3, and the calculation model (calculation conditions) was as follows.
[0008]
The fluorescent lamp 2 has a diameter of 2.6 mm and a luminance of 27500 [cd / m ² ], and this is arranged at a position where the distance H from the reflecting plate 5 is 4.0 mm and an arrangement pitch P is 23.2 mm, and 12 lamps are arranged. is doing. The size of the diffusion plate 3 is 40 cm wide × 30 cm high, and the distance T from the reflection plate 5 is 2 cm.
[0009]
The fluorescent lamp 2 emits light from the entire surface with a diffusive light distribution characteristic. The reflection plate 5 has a total reflectance of 97%, of which the diffuse reflection component is 96%. Is assumed to have a light transmittance of 60%, of which the diffusivity is 90%.
[0010]
Then, the luminance is calculated by dividing the light at the diffusion plate 3 into components, that is, the luminance component L2 due to the direct light from the fluorescent lamp 2 and the luminance component L1 due to the reflected light from the reflection plate 5 are obtained and synthesized. As a result, the luminance distribution L0 is obtained.
[0011]
As is apparent from FIG. 3, the luminance distribution characteristic L2 due to direct light has a peak at a position facing the fluorescent lamp 2, and the luminance component L1 due to reflected light is made uniform throughout the entire row. Yes. For this reason, the luminance distribution L0 is depressed at the midpoint of the arrangement pitch P of the fluorescent lamps 2, and the luminance is uneven.
[0012]
Various improvements and proposals have been made in the past in order to suppress the occurrence of such uneven brightness. As an example, there are inventions disclosed in each of the publications shown in Patent Document 1 to Patent Document 6.
[0013]
[Patent Document 1]
JP-A-6-258639
[Patent Document 2]
JP-A-10-39808
[Patent Document 3]
JP 2001-297613 A
[Patent Document 4]
JP 2002-169479 A
[Patent Document 5]
JP-A-7-270785
[Patent Document 6]
Real Kaihei 7-32636
[0014]
[Problems to be solved by the invention]
For example, in the invention disclosed in Patent Document 1, this luminance distribution can be made uniform by appropriately setting the positional relationship of the reflecting plate 5 and the diffusing plate 3 with respect to the row of fluorescent lamps 2. . However, according to the technical proposal, fluorescent lamps are arranged at a narrow pitch, and the increase in thickness and screen requires a large number of fluorescent lamps, which increases power consumption and weight, which is disadvantageous in terms of cost. Is not realistic.
[0015]
Further, techniques for making the luminance distribution uniform include printing a shielding pattern called a lighting curtain on the lower surface of the diffusion plate, and installing a prism sheet on the upper portion of the diffusion plate. However, since the lighting curtain reduces the brightness of other places according to the part where the brightness is lowest, the luminous efficiency is remarkably reduced, and the prism sheet is expensive, and the luminous efficiency is reduced due to the loss of the sheet itself. After all it decreases.
[0016]
On the other hand, there is an idea to improve the reflection characteristics by devising the shape and properties of the reflector. For example, the invention described in Patent Document 2 adopts a structure in which a specular reflection part is provided in a convex shape along the fluorescent lamp, and the invention described in Patent Document 3 has a structure in which a reflecting plate is provided in a curved shape having multiple faces with respect to the fluorescent lamp. Take. However, in these cases, it is difficult to obtain a desired reflection characteristic for a complicated shape, and the shape structure is complicated, which increases the cost.
[0017]
Further, as in the inventions disclosed in Patent Literature 4, Patent Literature 5, Patent Literature 6, and the like, there is an idea of improving the reflection characteristics by providing a specular reflection portion on the reflecting plate. However, since the reflection at the specular reflection part is highly condensing, it is difficult to obtain a uniform luminance distribution by simply providing the specular reflection part on the reflector, and an optical design that takes that point into consideration is necessary. become.
[0018]
The present invention has been made in view of the above-described background, and its object is to solve the above-described problems, adopt a relatively simple configuration, and evenly distribute the luminance distribution on the light-emitting surface. It is an object of the present invention to provide a backlight unit that can be obtained and can maintain good luminous efficiency.
[0019]
[Means for Solving the Problems]
In order to achieve the above-described object, in the backlight unit according to the present invention, a straight tube fluorescent lamp is used as a light source, and the fluorescent lamp is placed between a reflector plate and a light-transmissive diffuser plate facing each other in parallel. A plurality of backlight units, wherein the reflecting plate has a strip-like specular reflecting portion mainly for specular reflection at a misalignment position that does not face the fluorescent lamp, and other portions excluding the specular reflecting portion are The diffuse reflection portion is mainly diffused reflection, and the specular reflection portion includes an interval T between the reflection plate and the diffusion plate, an interval H between the reflection plate and the center of the fluorescent lamp, and the fluorescent lamp. With respect to the arrangement pitch P, a position that is (P × H) / 2 (T + H) from the position directly facing the fluorescent lamp is taken, and a width of (P / 4) or less is provided.
[0020]
Further, the reflection characteristics of the reflecting plate are preferably such that the specular reflection component in the total reflection rate is 80% or more in the specular reflection portion, and the diffuse reflection component in the total reflection rate is 80% or more in the diffuse reflection portion. A more preferable range is 95% or more.
[0022]
In the present invention, since the specular reflection part is provided at a position shifted from the fluorescent lamp, the specular reflection part can condense the reflected light that is specularly reflected at a specific position. The reflected light from the specular reflection part is strongly condensed at the midpoint of the array pitch P, which is the brightness reduction point, and compensates for the decrease in brightness at that position, and the position and width of the specular reflection part are appropriately adjusted. Adjustment is performed to optimally balance specular reflection and diffuse reflection on the reflection plate, thereby making the luminance distribution uniform.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 shows a first embodiment of the present invention. In the backlight unit according to the present embodiment, the main body 1 has a shallow dish shape with a raised peripheral edge, a plurality of fluorescent lamps 2 are arranged inside, and a light transmissive diffusion plate 3 is attached to the opening. These are the same as the conventional ones in FIG. Further, the inner surface of the main body 1 is a reflecting plate 10, but in the present invention, as shown in FIG. 5, the reflecting plate 10 is composed of two reflecting portions 11 and 12 having different characteristics, and the light from the fluorescent lamp 2 is diffused. 3 diffuses to obtain surface emission.
[0024]
That is, the reflecting plate 10 has a belt-like specular reflection part 12 mainly for regular reflection at a position where it does not face the fluorescent lamp 2, and the other parts except the specular reflection part 12 are diffuse reflection mainly for irregular reflection. It becomes the structure used as the part 11. FIG.
[0025]
As shown in FIG. 6, the specular reflection section 12 is related to the interval T between the reflector 10 and the diffusion plate 3, the interval H between the reflector 10 and the center of the fluorescent lamp 2, and the arrangement pitch P of the fluorescent lamp 2. The initial position is (P × H) / 2 (T + H) from the position directly facing the fluorescent lamp 2, and is provided with a width D2 of (P / 4) or less. This specular reflection part 12 can be formed by vapor-depositing silver or applying a silver foil tape.
[0026]
Since specular reflection is mainly performed in the specular reflection section 12, as shown in FIG. 7, the light can be condensed at a specific position, and in the present invention, the specular reflection portion 12 is strong at the intermediate point B of the array pitch P, which is a luminance reduction point. To compensate for the decrease in luminance at that position. In other words, the specular reflection unit 12 is basically provided at a position where the reflected light can be collected at the intermediate point B of the arrangement pitch P. However, an optimum solution can be obtained at the specular reflection point S determined geometrically. First, optimization is required with the regular reflection point S as the initial position.
[0027]
Since the initial position of the specular reflection unit 12 is the regular reflection point S shown in FIG. 6, the incident angle and the reflection angle have the same value θ at the regular reflection point S, and the optical path shown in FIG. θ). The distance T between the reflector 10 and the diffuser 3, the distance H between the reflector 10 and the center of the fluorescent lamp 2, the arrangement pitch P of the fluorescent lamp 2, and the regular reflection point from the directly facing position with the fluorescent lamp 2. When the distance to S (displacement position with respect to the fluorescent lamp 2) D1, the reflected light, the diffusion plate 3, and the right triangle by the normal line
tan θ = (P / 2−D1) / T
Is obtained. Similarly, tan θ = D1 / H by the right-angled triangle by the light toward the regular reflection point S, the normal line, and the perpendicular line from the normal line to the fluorescent lamp 2
And tan θ is eliminated from both equations, and D1 = (P × H) / 2 (T + H)
Get a relationship.
[0028]
As described above, the position of the specular reflection portion 12 with respect to the fluorescent lamp 2 is optimized at the geometric regular reflection point S as the initial position (D1), and then optimized. For this purpose, an optimum solution for obtaining a peak value can be obtained by obtaining a luminance distribution on the diffusion plate 3 by an experiment or simulation using a prototype and sequentially changing the deviation position D1 and the width D2 as parameters. decide.
[0029]
For example, the specular reflection unit 12 is a silver foil sheet, and the reflection plate 10 with the silver reflection sheet pasted at the shift position D1 is made as a trial, and the luminance distribution on the diffusion plate 3 is obtained by experiment. Here, if the brightness at the intermediate point B is insufficient, the width D2 of the specular reflection unit 12 is widened. Conversely, if the brightness is excessive, the width D2 is narrowed for adjustment. By this adjustment, the overall luminance distribution on the diffusing plate 3 is averaged, and when the luminance unevenness is recognized, an adjustment is performed to change the shift position D1 of the specular reflection unit 12.
[0030]
When the uniformity of luminance was measured using the deviation position D1 and the width D2 of the specular reflection section 12 as parameters, the characteristics shown in FIGS. 8 and 9 were confirmed. As is apparent from these graphs, the deviation position D1 and the width D2 both have peak values, and the optimum solution can be determined by the above-described optimization. Then, by appropriately adjusting the shift position D1 and the width D2, the diffuse reflection and the specular reflection can be balanced, and the light distribution can be made uniform as a whole.
[0031]
FIG. 10 is a graph showing luminance distribution characteristics in the backlight unit shown in FIG. This luminance distribution characteristic is also based on a simulation similar to the conventional example of FIG. 3 described above. The horizontal axis corresponds to the array of fluorescent lamps 2 shown in FIG. 11, the right end is the center position of the backlight unit, and the left end is the back. It corresponds to one side edge of the light unit. The vertical axis represents the luminance [cd / m ² ] on the diffusion plate 3, and the calculation model (calculation conditions) was as follows.
[0032]
The fluorescent lamp 2 has a diameter of 2.6 mm and a luminance of 27500 [cd / m ² ], and this is arranged at a distance H of 4.0 mm from the reflector 10 at an arrangement pitch P of 23.2 mm. is doing. The diffusion plate 3 is 40 cm wide × 30 cm high, and the distance T from the reflecting plate 10 is 2 cm.
The specular reflection portion 12 has a flat sheet shape, and the displacement position D1 with respect to the fluorescent lamp 2 is 3 mm, and the width D2 is 2 mm.
[0033]
The diffuse reflection part 11 of the reflector 10 has a total reflectance of 97%, of which the diffuse reflection component is 96%, and the specular reflection part 12 has a total reflectance of 95%, of which the specular reflection component is 96%. Shall be.
[0034]
Further, the fluorescent lamp 2 emits light from the entire surface with diffusive light distribution characteristics, and the diffusion plate 3 has a light transmittance of 60%, of which the diffusion rate is 90%.
[0035]
Then, the luminance calculation is made by dividing the light at the diffuser 3 by component, that is, the luminance component L2 due to the direct light from the fluorescent lamp 2 and the luminance component L1 due to the reflected light from the reflector 10 are obtained and synthesized. As a result, the luminance distribution L0 is obtained.
[0036]
As is apparent from FIG. 10, when the luminance distribution characteristic is observed, a peak appears in the luminance component L1 due to the reflected light at a predetermined pitch, which is synchronized with the under peak of the luminance component L2 due to the direct light. As a result, it can be seen that the luminance distribution L0 is a flat distribution.
[0037]
In this way, the belt-like specular reflection part 12 is provided at the deviation position D1 with respect to the fluorescent lamp 2, and the reflected light from the specular reflection part 12 is collected at a position where there is a drop in luminance (middle point B of the arrangement pitch P described above). Since it emits light, this is a compensation to compensate for the insufficient luminance, and thus the luminous efficiency can be kept good. In addition, the luminance distribution on the light emitting surface can be obtained uniformly without unevenness.
[0038]
Further, the reflecting plate 10 includes two reflecting portions 11 and 12 having different characteristics. Since the present invention optimizes the arrangement of the specular reflecting portion 12, the configuration itself is relatively simple. There is an advantage in cost because it is not necessary.
[0039]
The specular reflection unit 12 is not limited to a flat sheet shape. For example, it may be curved in a convex shape and can be changed as appropriate. In the reflected light by specular reflection, iridescent colors may appear, but here the color D does not appear because the width D2 of the specular reflection part 12 becomes sufficiently narrow.
[0040]
【The invention's effect】
As described above, in the backlight unit according to the present invention, the specular reflection part is provided at a position shifted from the fluorescent lamp, and thus the specularly reflected reflected light can be condensed at a specific position in the specular reflection part. And it concentrates strongly on the middle point of the arrangement pitch P, which is the luminance reduction point, and optimally balances the specular reflection and diffuse reflection on the reflector, so that the luminance distribution on the light emitting surface can be obtained evenly and uniformly. And the luminous efficiency can be kept good.
[0041]
In addition, the reflecting plate is composed of two different characteristics (diffuse reflecting portion and specular reflecting portion). Since the present invention optimizes the arrangement of the specular reflecting portion, the structure itself is relatively simple and advantageous in terms of cost. There is sex.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a conventional example of a direct type backlight unit.
FIG. 2 is a cross-sectional view showing reflection of light by a diffuse reflector.
FIG. 3 is a graph showing luminance distribution characteristics in the conventional example of FIG. 1;
FIG. 4 is a perspective view of a backlight unit showing the first embodiment.
FIG. 5 is a cross-sectional view illustrating a reflecting plate according to the present invention.
FIG. 6 is a cross-sectional view illustrating the position of a specular reflection unit.
FIG. 7 is a cross-sectional view showing reflection of light at a specular reflection unit.
FIG. 8 is a graph showing the uniformity of luminance with the shift position D1 of the specular reflection portion as a parameter.
FIG. 9 is a graph showing luminance uniformity using the width D2 of the specular reflection portion as a parameter.
10 is a graph showing luminance distribution characteristics in the backlight unit shown in FIG. 4; FIG.
11 is a cross-sectional view of the backlight unit shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main body 2 Fluorescent lamp 3 Diffusion plate 5 Reflection plate 10 Reflection plate 11 Diffuse reflection part 12 Specular reflection part

Claims (2)

A backlight unit in which a straight tube type fluorescent lamp is used as a light source, and a plurality of the fluorescent lamps are arranged between a reflecting plate and a light transmissive diffusing plate facing each other in parallel.
The reflection plate has a band-like specular reflection part mainly for regular reflection at a position not facing the fluorescent lamp, and the other part except the specular reflection part is a diffuse reflection part mainly for irregular reflection . ,
The specular reflection part is a positive distance from the fluorescent lamp with respect to an interval T between the reflector and the diffuser, an interval H between the reflector and the fluorescent lamp center, and an arrangement pitch P of the fluorescent lamp. A backlight unit having a position of (P × H) / 2 (T + H) from the opposite position and having a width of (P / 4) or less .   The reflection characteristic of the reflection plate is characterized in that the specular reflection component in the total reflection factor is 80% or more in the specular reflection part, and the irregular reflection component in the total reflection factor is 80% or more in the diffuse reflection part. Item 2. The backlight unit according to Item 1.

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