WO2011074644A1

WO2011074644A1 - Surface light source device, transparent image display device, and light source

Info

Publication number: WO2011074644A1
Application number: PCT/JP2010/072691
Authority: WO
Inventors: 裕次郎川口
Original assignee: 住友化学株式会社
Priority date: 2009-12-17
Filing date: 2010-12-16
Publication date: 2011-06-23
Also published as: TW201207292A; JP2011129371A; JP5075190B2

Abstract

The disclosed surface light source device (20) is a plurality of two-dimensionally arrayed light sources, wherein each of said plurality of light sources is a point light source. The light source device (20) is provided with said plurality of light sources (31), and a light diffusion plate (40) that diffuses the light from the plurality of light sources (31). In the surface light source device (20), the light distribution I(θ) of the individual light sources (31) of the plurality of light sources fulfils the formula below. I(θ) = (cos θ)^-2·{f(θ,0)}^-1p(θ) (In the formula: θ is the angle of light radiation from the aforementioned individual light sources (31); f(θ,0) is the forward-direction radiation-intensity function of the BTDF of the light diffusion plate (40); p(θ) is the forward-direction luminance profile of the aforementioned surface light source device (20) resulting from said individual light sources (31); and said forward-direction luminance profile is triangular, trapezoidal, or rectangular taking into account overlap for causing the forward-direction luminance of said surface light source device (20) to be constant.)

Description

Surface light source device, transmissive image display device, and light source

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, the periodic brightness non-uniformity that occurs because the brightness near the light source is high is a problem. By reducing the thickness of the surface light source device or reducing the number of light sources to reduce power consumption, The periodic brightness non-uniformity 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 side emission type as a light source of a transmissive image display device, it is possible to suppress non-uniform luminance without special processing of the light diffusion plate as in

Patent Documents

1 and 2. Can be considered. However, even if the LED of the bat wing type or the side emission type is used as it is, the effect of suppressing the uneven brightness is still low.

Accordingly, the present invention provides a surface light source device capable of suppressing nonuniform luminance 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 is to provide a light source for.

The surface light source device of the present invention is a plurality of light sources arranged two-dimensionally, each of the plurality of light sources being a point light source, and the light diffusion for diffusing the light from the plurality of light sources and the plurality of light sources A board. In the surface light source device of the present invention, the light distribution I (θ) of each light source among the plurality of light sources is set so as to satisfy the following expression.
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
(In the formula, θ is an emission angle of light from the individual light sources, f (θ, 0) is a front direction emission intensity function of BTDF of the light diffusion plate, and p (θ) is A front luminance profile of the surface light source device by individual light sources, the front luminance profile being triangular, trapezoidal, or rectangular in consideration of overlap in order to make the front luminance of the surface light source device constant Front luminance profile.)

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 output angle θ from the light source. It can be made constant without dependence. Further, in consideration of the overlap between adjacent light sources, the front luminance profile p (θ) of the surface light source device with one light source is made triangular, trapezoidal, or rectangular, 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, it is possible to suppress nonuniform brightness without performing special processing on the light diffusion plate.

It is preferable that the above-described emission intensity function f (θ, 0) in the front direction is obtained by measuring BTDF of the light diffusion plate, and the front luminance profile p (θ) is obtained by the following equation.
| θ | ≦ θ _x1
p (θ) = 1
In θ _x1 <| θ | ≦ ArcTan {(I−x ₁ ) / D},
p (θ) = (tan θ _I −tan θ _x1 −tan θ) / (tan θ _I −2 tan θ _x1 )
ArcTan {(I−x ₁ ) / D} ≦ | θ |
p (θ) = 0
(Wherein, I is an interval between the plurality of light sources, D is an interval between the plurality of light sources and the light diffusion plate, and x ₁ is the triangular shape, trapezoidal shape, or rectangular shape. The attenuation start position is a position in the arrangement direction of a plurality of light sources with reference to the positions of the individual light sources, and θ _x1 is the position relative to the attenuation start position x = x ₁ . The light emission angle of each light source, which is ArcTan (x ₁ / D), and θ _I is the individual with respect to a position x = I in the arrangement direction of a plurality of light sources with respect to the position of each light source. The light emission angle of the light source of (ArcTan (I / D)).
In the present specification, the position x = x ₁ and the position x = I are positions (coordinates) in the arrangement direction of a plurality of light sources with respect to the position of the target light source, in other words, from the target light source. Is a parameter representing the distance of. And, as in the above formula, these x ₁ and I may each be a numerical value.

A 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 above-described surface light source device.

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

The point light source of the present invention is a point light source for a surface light source device including 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) of the point light source of the present invention is set to satisfy the following expression.
I (θ) = (cos θ) ⁻² · {f (θ, 0)} ⁻¹ · p (θ)
(In the formula, θ is an emission angle of light from each of the plurality of light sources, f (θ, 0) is a BTDF front emission intensity function of the light diffusion plate, and p (θ) is a front luminance profile of the surface light source device by the individual light sources, and the front luminance profile is triangular or trapezoidal in consideration of overlap in order to make the front luminance of the surface light source device constant. Or a rectangular front luminance profile.)

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, it is possible to suppress uneven brightness of the surface light source device without requiring special processing on the light diffusion plate.

According to the present invention, it is possible to suppress uneven brightness of the surface light source device and the transmissive image display device without performing special processing on the light diffusion plate.

FIG. 1 is a cross-sectional view showing a configuration of a transmissive image display device and a surface light source device according to an embodiment of the present invention. FIG. 2 is a diagram showing the arrangement of light sources from above in the surface light source device according to the embodiment of the present invention. FIG. 3A is a diagram showing the luminance characteristics of a batwing type or side emission type LED, and FIG. 3B is a diagram showing the luminance characteristics of a Lambertian type LED. FIG. 4 is a diagram for explaining the light distribution characteristics of light emitted from one light source. FIG. 5 is a diagram for explaining light distribution characteristics on the light irradiation surface of the light diffusion plate. FIG. 6 is a diagram for explaining the dependency of the light diffusion plate on the emission angle of BTDF. FIG. 7 is a diagram for explaining the incident angle dependence of the BTDF front emission intensity of the light diffusion plate. FIG. 8 is a diagram for explaining light distribution characteristics of a combination of a light source and a light diffusing plate. FIG. 9 is a diagram for explaining light distribution characteristics of a combination of a plurality of light sources and a light diffusing plate. FIG. 10 is a diagram showing a front luminance profile p (θ) for each light source. FIG. 11 is a diagram showing a front luminance profile p (θ) for each light source. FIG. 12 is a diagram showing a measurement result of BTDFf (θ, ψ) of the light diffusion plate RM871S. FIG. 13 is a diagram showing a measurement result of BTDFf (θ, ψ) of the light diffusion plate RM861S. FIG. 14 is a diagram showing a measurement result of BTDFf (θ, ψ) of the light diffusion plate RM862S. FIG. 15 is a diagram showing a measurement result of BTDFf (θ, ψ) of the light diffusion plate RM863S. FIG. 16 is a diagram showing a measurement result of BTDFf (θ, ψ) of the light diffusion plate RM864S. FIG. 17 is a graph showing the light distribution I (θ) of the light source of Example 1. FIG. 18 is a graph showing the light distribution I (θ) of the light source of Example 2. FIG. 19 is a graph showing the light distribution I (θ) of the light source of Example 3. FIG. 20 is a graph showing the light distribution I (θ) of the light source of Example 4. FIG. 21 is a graph showing the light distribution I (θ) of the light source of Example 5. FIG. 22 is a graph showing the light distribution I (θ) of the light source of Example 6. FIG. 23 is a graph showing the light distribution I (θ) of the light source of Example 7. FIG. 24 is a graph showing the light distribution I (θ) of the light source of Example 8.

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. 1 is a cross-sectional view taken along the line SS in FIG. 2. In FIG. 1, the transmissive image display apparatus 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.

The liquid crystal cell 11 and the

polarizing plates

12 and 13 may be those used in a transmissive image display device such as a conventional liquid crystal display device. 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 I, the distance I is, for example, 15 mm to 150 mm. Although the bat wing type and side emission type LEDs have been exemplified as the light source 31, as shown in FIG. 3B (several types of luminance characteristics), a Lambertian type that emits light toward the top 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 disposed 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 diffusing 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 I between two adjacent

light sources

31, 31 is set so that the I / D is 1.5 or more, and preferably the I / 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, and has light deflection characteristics that allow light incident from an oblique direction to be deflected and emitted in the front direction. An optical deflection plate 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 is represented 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.

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, consider the light distribution characteristics of the light diffusion plate 40, that is, BSDF (Bidirectional Scattering Distribution Function), particularly BTDF (Bidirectional Transmission Distribution Function). FIG. 6 is a diagram for explaining the dependency of the light diffusion plate 40 on the emission angle of BTDF, and FIG. 7 is a diagram for explaining the dependency of the light diffusion plate 40 on the incidence angle of the emission intensity in the front direction of 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 (5).

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 rectangular, 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.

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 by 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 a normalized front luminance distribution for each light source 31 when the light source 31 is arranged at positions x =..., −3I, −2I, −I, 0, I, 2I, 3I,. 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), it is a position in the arrangement direction of the light sources 31 with respect to the position of each light source 31 and has a front luminance L. If the attenuation start position is x ₁ (0 ≦ x ₁ ≦ I / 2),
| x | ≦ x ₁
g (x) = 1,
x ₁ <| x | ≦ I−x ₁
g (x) = (I−x ₁ −x) / (I−2x ₁ )
In I−x ₁ <| x |
Let g (x) = 0.
As shown in FIG. 11, a normalized front luminance distribution g (x that is triangular when x ₁ = 0, trapezoidal when 0 <x ₁ <I / 2, and rectangular when x ₁ = I / 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 of the light source 31 with respect to the position I θ _I = ArcTan (I / D), and g (x) is converted into a function p (θ) of θ,
| θ | ≦ θ _x1
p (θ) = 1,
In θ _x1 <| θ | ≦ ArcTan {(I−x ₁ ) / D},
p (θ) = (tan θ _I −tan θ _x1 −tan θ) / (tan θ _I −2 tan θ _x1 ),
ArcTan {(I−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, it is possible to suppress uneven brightness 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, it is possible to suppress nonuniform luminance.

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, nonuniform brightness of the surface light source device 20 can be suppressed without requiring special processing on the light diffusion plate 40.

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, a method for setting the light distribution I (θ) of the light source 31 according to the present invention will be described more specifically based on Examples 1 to 8.
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 °, and BTDF (BSDF) f (θ, ψ) was obtained. 12 to 16 show the measurement results of BTDFf (θ, ψ) of each light diffusion plate 40. FIG. 12 to 16, the front-side outgoing intensity function f (θ, 0) of the 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 I / 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 brightness nonuniformity of the surface light source device 20 could 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 set to I / D = 3.0, and the attenuation start position in the front luminance profile p (θ) was set to 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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
(Example 3)

Next, a front luminance profile p (θ) was determined. In Example 3, the arrangement of the light source 31 was I / 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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
Example 4

Next, a front luminance profile p (θ) was determined. In Example 4, the arrangement of the light source 31 was I / 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 rectangular.

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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
(Example 5)

Next, a front luminance profile p (θ) was determined. In Example 5, the arrangement of the light source 31 was I / 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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
(Example 6)

Next, a front luminance profile p (θ) was determined. In Example 6, the arrangement of the light source 31 was I / 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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
(Example 7)

Next, a front luminance profile p (θ) was determined. In Example 7, the arrangement of the light source 31 was I / 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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.
(Example 8)

Next, a front luminance profile p (θ) was determined. In Example 8, the arrangement of the light sources 31 was I / 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 rectangular.

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 brightness nonuniformity of the surface light source device 20 could be reduced without performing special processing on the light diffusion plate 40.

In FIG. 17 to FIG. 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 °.

The present invention can be applied to the application of suppressing luminance unevenness of the surface light source device and the transmissive image display device without performing special processing on the light diffusion plate.

DESCRIPTION OF SYMBOLS 1 Transmission type image display apparatus 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 reflection member 40 Light diffusing plate

Claims

A plurality of light sources arranged two-dimensionally, each of the plurality of light sources being a point light source;
A light diffusing plate for diffusing light from the plurality of light sources;
In a surface light source device comprising:
A surface light source device in which a light distribution I (θ) of each of the plurality of light sources is set to satisfy the following expression.
I (θ) = (cos θ) −2 · {f (θ, 0)} −1 · p (θ)
(In the formula, θ is an emission angle of light from the individual light sources, f (θ, 0) is a front direction emission intensity function of BTDF of the light diffusion plate, and p (θ) is A front luminance profile of the surface light source device by individual light sources, the front luminance profile being triangular, trapezoidal, or rectangular in consideration of overlap in order to make the front luminance of the surface light source device constant Front luminance profile.)
The front-direction outgoing intensity function f (θ, 0) is obtained by measuring BTDF of the light diffusion plate,
The surface light source device according to claim 1, wherein the front luminance profile p (θ) is obtained by the following equation.
| θ | ≦ θ x1
p (θ) = 1
In θ x1 <| θ | ≦ ArcTan {(I−x 1 ) / D},
p (θ) = (tan θ I −tan θ x1 −tan θ) / (tan θ I −2 tan θ x1 )
ArcTan {(I−x 1 ) / D} ≦ | θ |
p (θ) = 0
(Wherein, I is an interval between the plurality of light sources, D is an interval between the plurality of light sources and the light diffusion plate, and x 1 is the triangular shape, trapezoidal shape, or rectangular shape. The attenuation start position is a position in the arrangement direction of the plurality of light sources with respect to the positions of the individual light sources, and θ x1 is relative to the attenuation start position x = x 1 The light emission angle of each individual light source is ArcTan (x 1 / D), and θ I is relative to a position x = I in the arrangement direction of the plurality of light sources with respect to the position of each individual light source. (An output angle of light of each individual light source, which is ArcTan (I / D).)
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 for a surface light source device comprising a plurality of light sources arranged two-dimensionally and a light diffusion plate for diffusing light from the light sources,
A point light source in which the light distribution I (θ) is set so as to satisfy the following expression.
I (θ) = (cos θ) −2 · {f (θ, 0)} −1 · p (θ)
(In the formula, θ is an emission angle of light from each of the plurality of light sources, f (θ, 0) is a BTDF front emission intensity function of the light diffusion plate, and p (θ) is a front luminance profile of the surface light source device by the individual light sources, and the front luminance profile is triangular or trapezoidal in consideration of overlap in order to make the front luminance of the surface light source device constant. Or a rectangular front luminance profile.)