JP5075190B2 - Surface light source device, transmissive image display device, and light source - Google Patents

Description

  The present invention relates to a surface light source device, a transmissive image display device including the surface light source device, and a light source for the surface light source device.

  In a transmissive image display device such as a liquid crystal display device, a direct type surface light source device is used as an example of a light source that outputs a backlight of a liquid crystal display unit. As a typical surface light source device, a device in which a plurality of light sources are arranged on the back side of a light diffusion plate is used. Such a surface light source device can easily increase the luminance of the light emitting surface by increasing the number of light sources to be arranged, but has a problem that the luminance uniformity is low. In particular, periodic luminance unevenness that occurs because the luminance near the light source becomes high is a problem. However, the periodic light source device can be reduced by reducing the number of light sources to reduce the thickness of the surface light source device or to reduce power consumption. Brightness unevenness has become a bigger problem.

  Therefore, in order to ensure the luminance uniformity, for example, in Patent Document 1, a light amount correction pattern is formed on the light diffusion plate corresponding to the distance from the light source. Similarly, in Patent Document 2, the light near the light source with a large amount of light is scattered by providing a sawtooth-shaped prism in a part near the light source on the side surface of the light diffusion plate.

JP-A-6-273760 JP 2004-127680 A

  By the way, in this type of transmissive image display device, instead of a linear light source such as a fluorescent lamp (cold cathode ray lamp), a point light source such as an LED capable of reducing power consumption has come to be used. Yes. As the LED, a Lambertian type aiming at emitting light toward directly above is widely known, but a bat wing type or side emission type aiming at emitting light in an oblique direction, etc. Has also been devised. By using an LED such as a batwing type or a side emission type as a light source of a transmissive image display device, it is possible to suppress luminance unevenness without applying special processing to the light diffusion plate as in Patent Documents 1 and 2. It is considered a thing. However, even if an LED such as a batwing type or a side emission type is used as it is, the effect of suppressing luminance unevenness is still low.

  Therefore, the present invention provides a surface light source device capable of suppressing luminance unevenness without performing special processing on the light diffusion plate, a transmissive image display device including the surface light source device, and the surface light source device. An object of the present invention is to provide a light source.

The surface light source device of the present invention is a point light source, and includes a plurality of light sources that are two-dimensionally arranged and a light diffusion plate that diffuses light from the plurality of light sources. Each of the light distributions I (θ) includes the light emission angle θ from each of the plurality of light sources, the BTDF front-side emission intensity function f (θ, 0) of the light diffusion plate, and the surface of each of the plurality of light sources. A front luminance profile of the light source device, based on the triangular, trapezoidal, or quadrangular front luminance profile p (θ) in consideration of overlap in order to make the front luminance of the surface light source device constant. Set to satisfy the expression,
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Surface light source device.

この式において、Ｉ(θ)＝（ｃｏｓθ）^−２・｛ｆ(θ，０)｝^−１とすれば、１光源による面光源装置の正面輝度Ｌを、光源からの光の出射角θに依存することなく一定にすることができる。更に、隣接する光源による重なりを考慮して、１光源による面光源装置の正面輝度プロファイルｐ(θ)を三角形状、台形状、又は、四角形状とすることにより、２次元配列された複数の光源を備える面光源装置の正面輝度を一定にすることができる。すなわち、Ｉ(θ)＝（ｃｏｓθ）^−２・｛ｆ(θ，０)｝^−１・ｐ(θ)とすれば、２次元配列された複数の光源を備える面光源装置の正面輝度を一定にすることができることとなる。 The front luminance L of the surface light source device with one light source is expressed by the following equation.

In this equation, if I (θ) = (cos θ) ⁻² · {f (θ, 0)} ^{− 1} , the front luminance L of the surface light source device with one light source is set to the light emission angle θ from the light source. It can be made constant without dependence. Further, in consideration of the overlap of adjacent light sources, the front luminance profile p (θ) of the surface light source device with one light source is made triangular, trapezoidal, or quadrangular, so that a plurality of light sources arranged two-dimensionally It is possible to make the front luminance of the surface light source device provided with constant. That is, if I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ), the front luminance of the surface light source device having a plurality of light sources arranged two-dimensionally is constant. Will be able to.

According to this surface light source device, the light distribution I (θ) of each of the plurality of light sources is
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Since it is set to satisfy, the front luminance can be made constant. Therefore, according to this surface light source device, luminance unevenness can be suppressed without performing special processing on the light diffusion plate.

The above-described emission intensity function f (θ, 0) in the front direction is obtained by measuring the BTDF of the light diffusing plate, and the front luminance profile p (θ) is determined by the interval l between the plurality of light sources, the plurality of light sources and the light diffusing plate. , The position in the arrangement direction of the plurality of light sources with reference to the positions of the plurality of light sources, and the attenuation start position x ₁ and the attenuation start position x in a triangular, trapezoidal, or quadrangular shape. a plurality of light sources each light emission angle theta _{x1 =} ArcTan for ₁ (x ₁ / _D), and, each of the plurality of light sources with respect to the position l in the arrangement direction of the plurality of light sources relative to the plurality of light sources of each position light Is preferably obtained by the following equation based on the exit angle θ ₁ = ArcTan (l / D).
| θ | ≦ θ _x1
p (θ) = 1
In θ _x1 <| θ | ≦ ArcTan {(l−x ₁ ) / D},
p (θ) = (tan θ ₁ −tan θ _x1 −tan θ) / (tan θ ₁ −2 tan θ _x1 )
ArcTan {(l−x ₁ ) / D} ≦ | θ |
p (θ) = 0

  The transmissive image display device of the present invention includes a transmissive image display cell and a surface light source device that supplies light to the transmissive image display cell, and includes the surface light source device described above.

  According to this transmissive image display device, since the above-described surface light source device is provided, luminance unevenness can be suppressed.

The light source of the present invention is a point light source, and is a light source for a surface light source device that includes a plurality of light sources arranged two-dimensionally and a light diffusion plate that diffuses light from the plurality of light sources. The light distribution I (θ) is determined by the light emission angle θ from each of the plurality of light sources, the BTDF front emission intensity function f (θ, 0) of the light diffusing plate, and the surface by the plurality of light sources. A front luminance profile of the light source device, based on the triangular, trapezoidal, or quadrangular front luminance profile p (θ) in consideration of overlap in order to make the front luminance of the surface light source device constant. It is set to satisfy the formula.
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)

According to this light source, the light distribution I (θ) is
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Therefore, the front luminance of the surface light source device can be made constant. Therefore, according to this light source, luminance unevenness of the surface light source device can be suppressed without requiring special processing on the light diffusion plate.

  According to the present invention, luminance unevenness of the surface light source device and the transmissive image display device can be suppressed without performing special processing on the light diffusion plate.

It is sectional drawing which shows the structure of the transmissive image display apparatus and surface light source device which concern on embodiment of this invention. It is a figure which shows the arrangement | sequence of the light source in the surface light source device which concerns on embodiment of this invention from upper direction. (A) is a figure which shows the luminance characteristic of LED of a batwing type or a side emission type, (b) is a figure which shows the luminance characteristic of LED of a Lambertian type. It is a figure for demonstrating the light distribution characteristic of the emitted light from 1 light source. It is a figure for demonstrating the light distribution characteristic in the light irradiation surface of a light diffusing plate. It is a figure for demonstrating the output angle dependence of BTDF of a light diffusing plate. It is a figure for demonstrating the incident angle dependence of the BTDF front direction output intensity of a light diffusing plate. It is a figure for demonstrating the light distribution characteristic of the combination of a light source and a light diffusing plate. It is a figure for demonstrating the light distribution characteristic of the combination of a several light source and a light diffusing plate. It is a figure which shows the front luminance profile p ((theta)) for every 1 light source. It is a figure which shows the front luminance profile p ((theta)) for every 1 light source. It is a figure which shows the measurement result of BTDFf ((theta), (psi)) of light diffusing plate RM871S. It is a figure which shows the measurement result of BTDFf ((theta), (psi)) of light diffusing plate RM861S. It is a figure which shows the measurement result of BTDFf ((theta), (psi)) of light diffusing plate RM862S. It is a figure which shows the measurement result of BTDFf ((theta), (psi)) of light diffusing plate RM863S. It is a figure which shows the measurement result of BTDFf ((theta), (psi)) of light diffusing plate RM864S. The figure which graphed the light distribution I ((theta)) of the light source of Example 1 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 2 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 3 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 4 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 5 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 6 is shown. The figure which graphed the light distribution I ((theta)) of the light source of Example 7 is shown. The figure which plotted the light distribution I ((theta)) of the light source of Example 8 is shown.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a cross-sectional view illustrating a configuration of a transmissive image display device and a surface light source device according to an embodiment of the present invention, and FIG. 2 illustrates an arrangement of light sources in the surface light source device according to the embodiment of the present invention from above. FIG. FIG. 1 is a cross-sectional view taken along the line II in FIG. 2. In FIG. 1, the transmissive image display device is shown in an exploded manner.

  The transmissive image display device 1 is, for example, a liquid crystal display device, and includes a transmissive image display unit 10 in which polarizing plates 12 and 13 are stacked on both upper and lower surfaces of a liquid crystal cell 11, and a rear surface side of the transmissive image display unit 10 ( And a direct-type surface light source device 20 provided on the lower side.

  As the liquid crystal cell 11 and the polarizing plates 12 and 13, those used in a transmissive image display device such as a conventional liquid crystal display device can be used. Examples of the liquid crystal cell 11 include known liquid crystal cells such as a TFT type and an STN type.

  The surface light source device 20 is a so-called direct-type surface light source device, and includes a light source unit 30 including a plurality of light sources 31 arranged in a two-dimensional manner. As the light source 31, as shown in FIG. 3A (several types of luminance characteristics), a point light source such as a batwing type or side emission type LED that emits light in an oblique direction is exemplified. The plurality of light sources 31 are arranged at substantially equal intervals. When the distance between the centers of two adjacent light sources 31 and 31 is l, the distance l is, for example, 15 mm to 150 mm. Although the bat wing type and side emission type LEDs are exemplified as the light source 31, as shown in FIG. 3B (several types of luminance characteristics), a lumbar cyan type that emits light directly upward is used. Various LEDs are applicable. Details of the light source 31 will be described later.

  The plurality of light sources 31 are supported by being arranged in the lamp box 32, and a light reflecting member 33 is preferably provided between the plurality of light sources 31 in the lamp box 32. Thereby, since the light output from each light source 31 is reliably output to the transmissive image display part 10 side, it becomes possible to use the light from each light source 31 efficiently.

  The surface light source device 20 includes a light diffusing plate 40 that is disposed away from the light source 31 on the front surface side (the upper side in FIG. 1) of the light source unit 30, that is, on the transmissive image display unit 10 side. . When the distance between the light diffusion plate 40 and the plurality of light sources 31 is D, the distance D is, for example, 5 mm to 50 mm. In the surface light source device 20, in order to reduce the thickness, the distance l between the two adjacent light sources 31, 31 is set so that l / D is 1.5 or more, and preferably l / D is 2.5 or more. And the separation distance D is selected.

  The light diffusing plate 40 does not project the image of each light source 31 onto the transmissive image display unit 10, so that the light from the light source unit 30, that is, the direct light from each light source 31 and the reflected light reflected by the light reflecting member 33. Is diffusely irradiated toward the transmissive image display unit 10. The thickness d of the light diffusing plate 40 is about 0.8 mm to 5 mm.

  The light diffusion plate 40 is made of a transparent material such as a transparent resin or transparent glass. Transparent resins include polycarbonate resin, ABS resin (acrylonitrile-styrene-butadiene copolymer resin), methacrylic resin, MS resin (methyl methacrylate-styrene copolymer resin), polystyrene resin, AS resin (acrylonitrile-styrene copolymer). Examples thereof include polyolefin resins such as coalesced resin), polyethylene, and polypropylene. In the light diffusing plate 40, a diffusing agent similar to the diffusing agent for diffusing light contained in a light diffusing plate used in a transmissive image display device such as a liquid crystal display device is appropriately added.

  The light diffusing plate 40 of the present invention is not limited to a diffusing plate to which diffusing agent particles are added (dope), but is an optical deflector capable of deflecting and emitting light incident from an oblique direction in the front direction. An optical deflector having characteristics is included.

  Next, the light source 31 will be described in detail. Each light source 31 has a light distribution distribution set so that the front luminance (that is, the emission intensity in the front direction) of the surface light source device 20 is constant, that is, the luminance unevenness of the surface light source device 20 is suppressed. Yes. Below, the setting method of the light distribution of each light source 31 is demonstrated.

  First, consider the light distribution characteristics of the light source 31. 4 is a diagram for explaining the light distribution characteristics of the light emitted from one light source 31, and FIG. 5 shows the light distribution on the light irradiation surface (light source side surface, lower surface of the drawing) of the light diffusion plate 40. It is a figure for demonstrating a characteristic.

As shown in FIG. 4, the luminous intensity I is expressed by a light flux Φ per unit solid angle Ω. The light distribution characteristic I (θ) is expressed by the following equation (1) as a function of the light emission angle θ.

よって、光拡散板４０に対する照度Ｅは下式（３）で表される。

As shown in FIG. 5, when the distance D between the light source 31 and the light diffusing plate 40 and the irradiation position x (x = 0 when θ = 0 °) of the light beam Φ having the emission angle θ are assumed to be light diffusing. The spread Δl of the light flux Φ on the plate 40 is expressed by the following equation (2).

Therefore, the illuminance E with respect to the light diffusing plate 40 is expressed by the following equation (3).

  Next, the light distribution characteristic of the light diffusion plate 40, that is, BSDF (Bidirectional Scattering Distribution Function), particularly BTDF (Bidirectional Transmission Distribution Function) is considered. FIG. 6 is a diagram for explaining the dependency of the light diffusion plate 40 on the emission angle of the BTDF, and FIG. 7 is a diagram for explaining the dependency of the light diffusion plate 40 on the emission angle in the front direction of the BTDF. It is.

As shown in FIG. 6, the light intensity Ii at the incident angle θ of light to the light diffusion plate 40 and the light intensity Io at the light emission angle ψ from the light diffusion plate 40 are functions f ( (θ, ψ) is expressed by the following formula (4).

As shown in FIG. 7, since the emission intensity in the front direction ψ = 0 ° is important as the front luminance of the surface light source device 20, the above equation (4) is changed to a function f (θ, 0) of the emission intensity in the front direction. When replaced, it is expressed by the following formula (4).

Next, consider the light distribution characteristics of the combination of the light source 31 and the light diffusion plate 40. FIG. 8 is a diagram for explaining the light distribution characteristics of the combination of the light source 31 and the light diffusing plate 40. The front luminance L is expressed by the following equation (6) from the above equations (3) and (5).

In the above equation (6), if I (θ) · cos ² θ · f (θ, 0) is constant regardless of θ, and if it is constant regardless of position x, the front luminance L is flat. Can be. That is, if the light distribution I (θ) satisfying the following expression (7) is set to the light distribution characteristic of the light source 31, the front luminance L can be made constant.

  Next, consider the light distribution characteristics of the combination of the plurality of light sources 31 and the light diffusion plate 40. FIG. 9 is a diagram for explaining the light distribution characteristics of the combination of the plurality of light sources 31 and the light diffusing plate 40. In the surface light source device 20, since the plurality of light sources 31 are arranged in a grid, it is necessary to consider the overlap of the front luminance profiles g (x) due to the adjacent light sources 31. For example, if the front luminance profile g (x) by each light source 31 is triangular, trapezoidal, or quadrangular, the front luminance is constant even in the overlapping portion of the front luminance profiles g (x) by the adjacent light sources 31. be able to.

すなわち、上式（８）を満たすような配光分布Ｉ(θ)を各光源３１の配光特性に設定すれば、正面輝度を一定にすることができることとなる。なお、配光分布Ｉ(θ)及び正面輝度プロファイルｐ(θ)としては、特に断りがない限り規格化した値が用いられる。 Here, since the position x in the arrangement direction of the light sources 31 and the emission angle θ of the light from the light sources 31 have a one-to-one correspondence, the front luminance profile g (x) is replaced with a function p (θ) of θ. Is possible. By multiplying the above equation (7) by this p (θ), the following equation (8) is obtained.

That is, if the light distribution I (θ) that satisfies the above equation (8) is set to the light distribution characteristic of each light source 31, the front luminance can be made constant. As the light distribution I (θ) and the front luminance profile p (θ), normalized values are used unless otherwise specified.

  Specifically, first, the BTDF front emission intensity function f (θ, 0) of the light diffusing plate 40 is measured using, for example, a goniophotometer for the BTDF (or BSDF) of the light diffusing plate to be used. By seeking.

  Next, the front luminance profile p (θ) is obtained as follows based on the desired front luminance profile. 10 and 11 are diagrams showing the front luminance profile p (θ). FIG. 10 shows the normalized front luminance distribution for each light source 31 when the light source 31 is arranged at positions x =..., −3 l, −2 l, −l, 0, l, 2 l, 3 l,. g (x), that is, the front luminance profile p (θ) is shown.

For example, as shown in FIG. 10, when it is desired to obtain a trapezoidal normalized front luminance distribution g (x), the position in the arrangement direction of the light sources 31 with respect to the position of each light source 31 and the front luminance L If the attenuation start position is x ₁ (0 ≦ x ₁ ≦ l / 2),
| x | ≦ x ₁
g (x) = 1,
In x ₁ <| x | ≦ l−x ₁ ,
g (x) = (l−x ₁ −x) / (l−2x ₁ )
In l−x ₁ <| x |
Let g (x) = 0.
As shown in FIG. 11, the normalized front luminance distribution g (x (x) is triangular when x ₁ = 0, trapezoidal when 0 <x ₁ <l / 2, and square when x ₁ = l / 2. ) Can be obtained.

Here, since tan θ = x / D, the light emission angle θ _x1 of the light source 31 with respect to the attenuation start position x ₁ = ArcTan (x ₁ / D), and the light emission angle θ ₁ of the light source 31 with respect to the position l = ArcTan (l / D), and g (x) is converted into a function p (θ) of θ,
| θ | ≦ θ _x1
p (θ) = 1,
In θ _x1 <| θ | ≦ ArcTan {(l−x ₁ ) / D},
p (θ) = (tan θ ₁ −tan θ _x1 −tan θ) / (tan θ ₁ −2 tan θ _x1 ),
ArcTan {(l−x ₁ ) / D} ≦ | θ |
p (θ) = 0.

  In this way, by calculating the front direction emission intensity function f (θ, 0) of the BTDF of the light diffusing plate 40 by actual measurement and determining the front luminance profile p (θ) by each light source 31, from the above equation (8), The setting of the light distribution I (θ) of each light source 31 can be obtained.

  The setting of the obtained light distribution I (θ) of each light source 31 can be realized by, for example, a resin shape covering the semiconductor chip in the LED or a lens shape provided on the light emitting surface side of the semiconductor chip.

Thus, according to the surface light source device 20 of the present embodiment, the light distribution I (θ) of each of the plurality of light sources 31 is
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Since it is set to satisfy, the front luminance can be made constant. Therefore, according to the surface light source device 20 of the present embodiment, luminance unevenness can be suppressed without performing special processing on the light diffusion plate 40.

  Further, according to the transmissive image display device 1 of the present embodiment, since the surface light source device 20 is provided, luminance unevenness can be suppressed.

Further, according to the light source 31 of the present embodiment, as described above, the light distribution I (θ) is
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Therefore, the front luminance of the surface light source device can be made constant. Therefore, according to the light source 31 of the present embodiment, luminance unevenness of the surface light source device 20 can be suppressed without requiring special processing on the light diffusion plate 40.

しかしながら、光拡散板としては、透明材料に拡散剤粒子を分散したものを使用することが多く、この種の光拡散板では、規定の全光線透過率になるように拡散剤濃度を設定すると、ＢＳＤＦ、すなわちＢＴＤＦを自由に設定することが困難となる。したがって、本発明のように、各光源３１に配光分布Ｉ(θ)を設定することが好ましい。 According to the idea of the present invention, it is also possible to set the BTDF front emission intensity function f (θ, 0) of the BTDF of the light diffusing plate 40 based on the following equation (9) obtained by modifying the above equation (8). It is done.

However, as the light diffusing plate, a material in which diffusing agent particles are dispersed in a transparent material is often used. With this type of light diffusing plate, when the diffusing agent concentration is set so as to have a prescribed total light transmittance, It becomes difficult to set BSDF, that is, BTDF freely. Therefore, it is preferable to set the light distribution I (θ) for each light source 31 as in the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made.

Hereinafter, based on Examples 1-8, the setting method of the light distribution I ((theta)) of the light source 31 of this invention is demonstrated more concretely.
Example 1

First, BTDFf (θ, ψ) of the light diffusion plate 40 was measured. As the light diffusion plate 40, the following five types of Sumipex (registered trademark) E manufactured by Sumitomo Chemical Co., Ltd. were used.
RM871S (thickness 2 mm, total light transmittance Tt = 53%)
RM861S (thickness 2 mm, total light transmittance Tt = 55%)
RM862S (thickness 2 mm, total light transmittance Tt = 60%)
RM863S (thickness 2 mm, total light transmittance Tt = 65%)
RM864S (thickness 2 mm, total light transmittance Tt = 70%)
As a measuring device, a GC5000L type variable angle photometer manufactured by Nippon Denshoku Industries Co., Ltd. was used, and a transmission measurement mode was used. In addition, the angle of the light source was changed manually, and the incident angle θ of the light was set from 0 ° to 75 ° at intervals of 5 °. For each incident angle θ, measurement was performed in the range of the emission angle ψ = −85 ° to 85 ° to obtain BTDF (BSDF) f (θ, ψ). 12 to 16 show the measurement results of BTDFf (θ, ψ) of each light diffusion plate 40. FIG. 12 to 16, a front-side outgoing intensity function f (θ, 0) of BTDF was obtained from the measurement result of the square frame portion, that is, the outgoing angle ψ = 0 °.

Next, a front luminance profile p (θ) was determined. In Example 1, the arrangement of the light source 31 was 1 / D = 3.0, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 0.0D. That is, the front luminance profile p (θ) is triangular.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). FIG. 17 is a graph of the obtained I (θ). By setting the light distribution I (θ) shown in FIG. 17 for each light source 31, the front luminance of the surface light source device 20 can be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 2)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 2, the arrangement of the light source 31 was 1 / D = 3.0, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 0.5D. That is, the front luminance profile p (θ) was trapezoidal.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). FIG. 18 is a graph of the obtained I (θ). By setting the light distribution I (θ) shown in FIG. 18 for each light source 31, the front luminance of the surface light source device 20 could be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 3)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 3, the arrangement of the light source 31 was 1 / D = 3.0, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 1.0D. That is, the front luminance profile p (θ) was trapezoidal.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). In FIG. 19, the obtained I (θ) is graphed. By setting the light distribution I (θ) shown in FIG. 19 for each light source 31, the front luminance of the surface light source device 20 could be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
Example 4

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 4, the arrangement of the light source 31 was 1 / D = 3.0, and the attenuation start position in the luminance profile p (θ) was x ₁ = 1.5D. That is, the front luminance profile p (θ) is a square shape.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). FIG. 20 is a graph of the obtained I (θ). By setting the light distribution I (θ) shown in FIG. 20 for each light source 31, the front luminance of the surface light source device 20 can be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 5)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 5, the arrangement of the light source 31 was 1 / D = 4.5, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 0.0D. That is, the front luminance profile p (θ) is triangular.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). FIG. 21 is a graph of the obtained I (θ). By setting the light distribution I (θ) shown in FIG. 21 for each light source 31, the front luminance of the surface light source device 20 can be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 6)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 6, the arrangement of the light source 31 was 1 / D = 4.5, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 0.75D. That is, the front luminance profile p (θ) was trapezoidal.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). FIG. 22 is a graph of the obtained I (θ). By setting the light distribution I (θ) shown in FIG. 22 for each light source 31, the front luminance of the surface light source device 20 could be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 7)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 7, the arrangement of the light source 31 was 1 / D = 4.5, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 1.5D. That is, the front luminance profile p (θ) was trapezoidal.

Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). In FIG. 23, the obtained I (θ) is graphed. By setting the light distribution I (θ) shown in FIG. 23 for each light source 31, the front luminance of the surface light source device 20 can be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.
(Example 8)

  First, as in Example 1, the BTDF front-direction emission intensity function f (θ, 0) of the light diffusing plate 40 was obtained from actual measurement.

Next, a front luminance profile p (θ) was determined. In Example 8, the arrangement of the light source 31 was 1 / D = 4.5, and the attenuation start position in the front luminance profile p (θ) was x ₁ = 2.25D. That is, the front luminance profile p (θ) is a square shape.

  Next, using the obtained p (θ) and f (θ, 0), the light distribution I (θ) of each light source 31 was obtained from the above equation (8). In FIG. 24, the obtained I (θ) is graphed. By setting the light distribution I (θ) shown in FIG. 24 for each light source 31, the front luminance of the surface light source device 20 can be made constant without depending on the emission angle θ. That is, the luminance unevenness of the surface light source device 20 can be reduced without performing special processing on the light diffusion plate 40.

  In FIGS. 17 to 24, the reason why the fluctuation is large in the vicinity of the emission angle θ = 0 ° A with respect to the light diffusion plates RM863S and RM864S is that RM863S and RM864S have relatively high transparency as shown in FIGS. Therefore, it can be considered that there are many unclear components. Accordingly, when using a light diffusion plate having a relatively high transparency, it is considered necessary to finely adjust the light distribution in the vicinity of the emission angle θ = 0 °.

  DESCRIPTION OF SYMBOLS 1 ... Transmission type image display apparatus 1, 10 ... Transmission type image display part, 11 ... Liquid crystal cell, 12, 13 ... Polarizing plate, 20 ... Surface light source device, 30 ... Light source part, 31 ... Light source, 32 ... Lamp box, 33 ... light reflecting member, 40 ... light diffusion plate.

Claims (4)

A plurality of light sources arranged in a two-dimensional manner,
A light diffusing plate for diffusing light from the plurality of light sources;
In a surface light source device comprising:
The light distribution I (θ) of each of the plurality of light sources is an emission angle θ of light from each of the plurality of light sources, a front direction emission intensity function f (θ, 0) of the BTDF of the light diffusion plate, and the A front luminance profile of the surface light source device by each of a plurality of light sources, the front luminance profile p having a triangular shape, a trapezoidal shape, or a quadrangular shape in consideration of overlap in order to make the front luminance of the surface light source device constant. Based on (θ), set to satisfy the following formula,
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
Surface light source device. The front-direction outgoing intensity function f (θ, 0) is obtained by measuring BTDF of the light diffusion plate,
The front luminance profile p (θ) includes an interval l between the plurality of light sources, an interval D between the plurality of light sources and the light diffusing plate, and an arrangement direction of the plurality of light sources based on the positions of the plurality of light sources. a position, the triangular, trapezoidal, or the position _{x 1} of rectangular attenuation start, the plurality of light sources each light emission angle theta _x1 = ArcTan respect to the position _{x 1} of the attenuation start _{(x 1} / D), and an emission angle θ ₁ of each of the plurality of light sources with respect to a position l in the arrangement direction of the plurality of light sources with respect to the position of each of the plurality of light sources, based on ArcTan (l / D). Obtained by the following formula,
| θ | ≦ θ _x1
p (θ) = 1
In θ _x1 <| θ | ≦ ArcTan {(l−x ₁ ) / D},
p (θ) = (tan θ ₁ −tan θ _x1 −tan θ) / (tan θ ₁ −2 tan θ _x1 )
ArcTan {(l−x ₁ ) / D} ≦ | θ |
p (θ) = 0
The surface light source device according to claim 1. A transmissive image display cell;
A surface light source device for supplying light to the transmissive image display cell, wherein the surface light source device according to claim 1;
A transmissive image display device. A point light source, which is a light source for a surface light source device including a plurality of light sources arranged two-dimensionally and a light diffusion plate for diffusing light from the plurality of light sources,
The light distribution I (θ) is an emission angle θ of light from each of the plurality of light sources, a front direction emission intensity function f (θ, 0) of the BTDF of the light diffusing plate, and the plurality of light sources. A front luminance profile of the surface light source device, based on the front luminance profile p (θ) in a triangular shape, trapezoidal shape, or quadrangular shape in consideration of overlap in order to make the front luminance of the surface light source device constant. It is set to satisfy the following formula,
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
light source.

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