JP2003203502A - Direct type surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct under type surface light source device which allows uniform illumination with a short optical path length and with a simple configuration. <P>SOLUTION: The direct under type surface light source device 10 comprises at least one LED 12 mounted on a printed board 11 such that the optical axis is perpendicular thereto, and an light-diffusing member 15 spaced above the LED 12. A prism array 14 having a prism on the surface facing toward the LED 12 is provided between the LED 12 and the light-diffusing member 15. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called direct type surface light source device for back illuminating a display such as a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a surface light source device for performing back illumination of a liquid crystal display device (LCD), there is a surface light source device provided with a surface emitting CFL or LED provided below an LCD panel. Particularly, as a surface light source device for a small-sized liquid crystal display device for a viewfinder, a surface light source device using an LED having a simple driving circuit has been widely used.

Such surface light source devices are classified into a direct type in which the directivity of the LED is arranged vertically with respect to the LCD panel and a sidelight type in which the directivity of the LEDs is arranged horizontally. The sidelight type surface light source device is configured, for example, as shown in FIG. In FIG. 5, the side light type surface light source device 1 includes a case 2
A reflection sheet 3, a light guide member 4, a sheet-shaped light diffusion member 5, and two prism sheets 6a and 6b, which are sequentially arranged in the inside.
And one LED 7 as a light source, which is arranged to face one side surface of the light guide member 4, and a cover 8 which covers the upper surface of the case 2.

The reflection sheet 3 is disposed so as to face the lower surface of the light guide member 4, and reflects the light emitted downward from the lower surface of the light guide member 4 so as to enter the light guide member 4. It has become. The light guide member 4 is made of a translucent material formed in a wedge shape having a flat cross section so that the light guide member 4 gradually becomes thinner toward one side (the right side in the figure). The light diffusing member 5 is arranged so as to face the upper surface of the light guide member 4, and diffuses the light emitted upward from the upper surface of the light guide member 4 and irradiates the light upward.

The prism sheets 6a and 6b are configured to have a light-collecting property by a prism shape, and impart light-collecting property to the light passing through the light diffusing member 5. The LED 7 is mounted on the flexible printed circuit board 7a in the case of the figure, and is driven by a driving voltage supplied from the outside through a conductive pattern on the flexible printed circuit board 7a to be laterally (right side in the case of the figure). ) Towards the light. The cover 8 is provided with a frame-shaped hole 8a and regulates light passing through the prism sheets 6a and 6b to define an illumination range of a predetermined size.

According to the side-light type surface light source device 1 having such a configuration, a part of the light emitted from the LED 7 enters the light guide member 4 from the side surface on one side.
Then, the light that has entered the light guide member 4 enters the upper surface or the lower surface of the light guide member 4, but at this time, the light that has entered at an incident angle equal to or greater than the critical angle is totally reflected and the inside of the light guide member 4 is reflected. Back to
Further, light incident at an incident angle less than the critical angle is emitted from the light guide member 4. As a result, a part of the light entering the light guide member 4 is directly emitted from the upper surface of the light guide member 4, a part of the light is reflected by the upper surface or the lower surface of the light guide member 4, or a part of the light is guided. The light is emitted downward from the lower surface of the light member 4, is reflected by the reflection member 3, is made incident again into the light guide member 4, and
Is emitted from the upper surface of.

The light emitted from the upper surface of the light guide member 4 is diffused and uniformized when passing through the light diffusing member 5, and is further condensed by the prism sheets 6a and 6b, which is not shown in the LCD panel. It will be incident on the display from the back. Accordingly, the display is the surface light source device 1
Is back-illuminated by the light from the light source, and the light that illuminates the display back-illuminated is made uniform by the propagation in the light guide member 4 and the diffusion by the light diffusion member 5, so that the entire display is substantially uniform. The backlight is illuminated with brightness, and the orientation of the prism sheets 6a and 6b is controlled, so that the brightness of the backlight is improved.

On the other hand, the direct type surface light source device is shown in FIG.
It is configured as shown in. In FIG. 6, the direct type surface light source device 9 includes one LED 7 ′, a light diffusing member 5, two prism sheets 6 a and 6 b, which are sequentially arranged in the concave portion 2 a of the case 2, and the concave portion of the case 2. The reflecting sheet 3a is arranged on the inner surface of the portion 2a, and the cover 8 covers the upper surface of the case 2. In this case, LED7 '
Is mounted on the printed circuit board 7b attached to the bottom surface of the case 2 by sticking or the like, and is thus arranged to project into the recessed portion 2a of the case 2. In addition, the reflection sheet 3a is provided in the recessed portion 2a of the case 2 so that the LED
It is arranged so as to surround 7 '.

According to the direct type surface light source device 9 having such a structure, a part of the light emitted from each LED 7'is directly incident on the light diffusing member 5 and the other part is reflected by the reflection sheet 3a. The light is reflected, enters the light diffusing member 5, is diffused by the light diffusing member 5, and then is condensed by the prism sheets 6a and 6b to back-illuminate the LCD panel from the lower surface. In this case, since the LEDs 7'are mounted upward on the printed circuit board 7b, the arrangement density of the LEDs 7'can be increased and the light guide member 4 can be provided.
Since it does not use, the loss of light is small and it is easy to achieve high brightness.

[0010]

By the way, in the sidelight type surface light source device 1 described above, since the light guide member 4 is used, light absorption by the residual stress in the light guide member 4 and scattering by the material are performed. Optical loss such as loss and Fresnel loss will occur. Therefore, there is a problem that the light extraction efficiency becomes low and the brightness of the back lighting becomes low. Further, the side light type surface light source device 1
If the LCD panel is backlit by
The polarizing plate attached to the panel performs light selection for transmitting only P-polarized light or S-polarized light out of the back illumination light and normally uses a halogen substance such as iodine or a dichroic absorbing dye itself. Absorbs light,
The light transmittance is low, and the light extraction efficiency is further reduced in combination with the light selection by the polarizing plate.

Further, in the case of a color LCD panel, since the shape of the pixel becomes smaller, the aperture ratio becomes smaller, and the use of a color filter further lowers the transmittance of back illumination light. Therefore, color L
In order to compensate for the low light transmittance of the CD panel, it is necessary to increase the number of LEDs used and the drive current to each LED, which increases the size of the surface light source device and increases power consumption. Also, reliability is lowered due to temperature rise, and material cost and assembly cost are increased.

On the other hand, in the direct type surface light source device 9 described above, the light emitted from each LED 7'propagates to the light diffusing member 5 in the space while spreading according to the directivity peculiar to the LED, so that the sidelight type surface is used. Compared to the light source device 1, light loss is small and light extraction efficiency is relatively high.

However, in such a direct type surface light source device 9, in order to obtain uniform back illumination, L
Since it is necessary to increase the distance (optical path length) from the ED 7 ′ to the light diffusion member 5, the entire device becomes thicker than the side light type surface light source device. Further, in order to suppress the uneven brightness, it is difficult to equalize the directivity near the optical axis only with the LED 7 '. For this reason, it is also known to dispose a white or gray-white light attenuating sheet immediately above the LED 7 ', but since the light attenuating sheet causes a large attenuation of luminance, it is the same as the sidelight type surface light source device. The brightness is about the same.

From the above points of view, it is an object of the present invention to provide a direct type surface light source device capable of performing uniform illumination with a simple structure even with a short optical path length. .

[0015]

According to the present invention, the above object is to provide at least one LED mounted on a printed circuit board so that an optical axis thereof is vertical, and a light spaced above the LED. A direct type surface light source device including a diffusing member, characterized in that a prism array having a prism on a surface facing the LED is provided between the LED and the light diffusing member. This is achieved by the light source device.

In the direct type surface light source device according to the present invention, preferably, the prism array is arranged at a position where the distance d from the LED is L / 2 or less with respect to the distance L from the LED to the light diffusing member. There is.

The direct type surface light source device according to the present invention preferably comprises, around the LED, a light diffusing surface for diffusing light from the LED upward.

The direct type surface light source device according to the present invention preferably comprises, around the LED, a reflecting portion for reflecting the light from the LED upward.

In the direct type surface light source device according to the present invention, preferably, the reflecting portion is a sheet-like reflecting member.

In the direct type surface light source device according to the present invention, preferably, the reflection portion is a reflection film provided on the inner surface of the case surrounding the LED.

According to the above structure, a part of the light emitted from each LED enters the prism array and is diffused in the direction perpendicular to the prism direction of the prism array. Then, the light diffused by the prism array is diffused and made uniform when passing through the light diffusing member, and is emitted upward.

As a result, in the light emitted from each LED, the effect of the bright line in the optical axis direction due to the directivity of each LED is reduced by the prism array and the light diffusing member, and a more uniform and high output surface is obtained. A light source will be obtained.
Therefore, even if the distance between each LED and the light diffusing member is relatively short, the light emitted from each LED reaches the light diffusing member after being diffused by the prism array, so that a uniform surface light source is obtained as a whole. Will be done.

In the prism array, the distance d from the LED is L / L with respect to the distance L from the LED to the light diffusing member.
When it is arranged at the position of 2 or less, the light sufficiently diffused by the prism sheet enters the light diffusing member, so that a more uniform surface light source as a whole can be obtained. .

When a light diffusing surface for diffusing light from the LED upward is provided around the LED, a part of the light emitted from the LED is diffused and reflected by the light diffusing surface. , Enters the light diffusing member via the prism array. As a result, the efficiency of extracting light from the LED is improved, and a surface light source with higher brightness can be obtained.

In the case where a reflective portion for reflecting light from the LED upward, preferably a sheet-shaped reflective member or a reflective film provided on the inner surface of the case surrounding the LED, is provided around the LED. , A part of the light emitted from the LED is reflected by the reflecting portion and enters the light diffusing member via the prism array. As a result, the efficiency of extracting light from the LED is improved, and a surface light source with higher brightness can be obtained.

As described above, according to the direct type surface light source device of the present invention, by providing the prism array directly above the LEDs, the directivity in the vicinity of the optical axis of each LED is diffused and leveled by the prism array. It will be. Therefore, it is possible to obtain the uniform and high-output surface light source by suppressing the influence of the bright line in the optical axis direction of each LED without significantly reducing the brightness.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to FIGS. still,
The embodiments described below are preferable specific examples of the present invention, and therefore, various technically preferable limitations are given,
The scope of the present invention is not limited to these embodiments unless otherwise specified in the description below.

1 to 3 show the construction of an embodiment of a direct type surface light source device according to the present invention. 1 to 3
In the direct type surface light source device 10, in order from the bottom,
Flexible printed circuit board 11, LED1 as a light source
2, a case 13, a prism array 14, a sheet-like light diffusing member 15, two prism sheets 16a and 16b and a cover 17, and a reflection sheet 18 arranged on an inner surface of a recess 13a (described later) of the case 13, It consists of

The flexible printed circuit board 11 is a flexible printed circuit board having, for example, polyimide or polyester as a base material, and has a mounting portion 11a on which the LED 12 is mounted and a lead wire portion 11 extending from the mounting portion 11a.
b and the mounting portion 11a of the LED 12
After mounting, is attached to the bottom surface of the case 13 by pasting, bonding or the like.

The LED 12 is a so-called surface mounting type LED, and is the mounting portion 1 of the flexible printed circuit board 11.
It is mounted on 1a so that the optical axis is vertically upward.

As shown in FIG. 2 and FIG. 3, the case 13 is formed in a flat rectangular parallelepiped shape, and has a substantially rectangular recess 13 formed so as to expand upward inward.
a.

As shown in FIG. 4, the prism array 14 has a prism 14a (FIG.
(See (C)). Here, the prism 14a
Has a vertical angle formed at right angles, and the prism direction thereof extends in the left-right direction in FIG. 4 (A). And
The distance d from the LED 12 of the prism 14a is L
With respect to the distance L from the ED 12 to the light diffusing member 15, it is arranged at a position such that [Equation 1] d ≦ L / 2.

The light diffusing member 15 is arranged on the upper surface of the case 13, and diffuses the light emitted upward from the prism array 14 and irradiates the light upward.

The prism sheets 16a and 16b are arranged on the light diffusing member 15 in an overlapping manner, and like the prism array 14, a prism made of an acrylic photocurable resin is provided on the surface of the PET base material. It is configured. Here, the prisms of the prism sheets 16a and 16b are formed such that the apex angles thereof are right angles,
The prism direction of one prism sheet 16a or 16b is arranged in parallel to the prism direction of the prism array 14, and the prism direction of the other prism sheet 16b or 16a is arranged to be perpendicular to the prism direction of the prism array 14. Thereby, the prism sheet 16
The a and 16b are configured to give the light passing through the light diffusing member 15 a light converging property.

The cover 17 is provided with a frame-shaped hole 17a and is placed on the upper surface of the case 13 from above the light diffusion member 15 and the prism sheets 16a and 16b. The light passing through 16b is regulated to define an illumination range of a predetermined size.

The reflection sheet 18 is attached to the inner surface of the recess 13a of the case 13 by sticking, bonding, or the like, and is composed of, for example, a dielectric multilayer film that performs regular reflection.

A direct type surface light source device 1 according to the embodiment of the present invention.
0 is configured as described above. Part of the light emitted from the LED 12 directly enters the prism array 14, and the other part of the light is reflected by the reflection sheet 18 and enters the prism array 14. . Then, the light incident on the prism array 14 is divided and diffused by each prism 14a of the prism array 14 in the direction perpendicular to the prism direction.

At this time, the light emitted vertically from the LED 12 is divided by the prism array 14 so that the strongest emission direction φ is expressed by [Equation 2] φ = arcsin [n · cos {(θ / 2)
+ Arcsin (cos (θ / 2) / n}], where n is the refractive index of the prism array and θ is the prism apex angle of the prism array, and therefore prism array 14 and prism sheet 16a, 1
When 6b has the same refractive index and the prisms have the same apex angle, the light emitted upward from the prism sheet 16b has the maximum brightness.

The light diffused by the prism array 14 is further incident on the light diffusing member 15, and the light diffusing member 1
After being diffused and homogenized when passing through 5, the light is further condensed by the prism sheets 16a and 16b and emitted upward, so that, for example, the LCD panel is back-illuminated from the lower surface.

In this case, since the prism array 14 is arranged between the LED 12 and the light diffusing member 15, the light emitted from the LED 12 is divided and diffused by the prism array 14. This allows the LED
The directivity in the optical axis direction of 12 is averaged by being divided and diffused by the prism array 14 and further diffused in all directions by the light diffusing member 15. Therefore, the LED
The influence of the bright line in the optical axis direction due to the directivity of 12 is reduced, and a more uniform and high-output surface light source can be obtained.

Further, since the prism array 14 is arranged between the LED 12 and the light diffusing member 15,
Even if the distance between the LED 12 and the light diffusion member 15 is short,
The light from the LED 12 is sufficiently diffused so that the light diffusion member 15
Incident on. As a result, the uneven brightness is represented by [Formula 3] uneven brightness = (maximum in-plane brightness-minimum in-plane brightness).
/ (Maximum luminance in plane + minimum luminance in plane) × 100 (%), the luminance unevenness in the direct type surface light source device 10 according to the embodiment of the present invention is the same as that of the conventional direct type shown in FIG. Compared with the surface light source device 9, it is about 1/2,
The average luminance about 1.5 times that of the sidelight type surface light source device 1 shown in FIG. 5 can be obtained. Further, the direct type surface light source device 10 according to the embodiment of the present invention is, for example, about 70% thinner than the conventional direct type surface light source device 9 shown in FIG. 6, that is, the side light type shown in FIG. The surface light source device 1 can be configured to have almost the same thickness.

As described above, according to the direct type surface light source device 10 according to the embodiment of the present invention, even if the direct type surface light source device 10 is configured to be relatively thin, the prism array 14 divides / diffuses the light so that the uneven brightness is small and the brightness is high. Since the surface light source having the brightness can be configured, the light guide member such as the saddle type surface light source device is not necessary, and the cost can be reduced. In addition, since the brightness is high, in order to obtain the same brightness, the LED
Brightness can be reduced, power consumption is reduced, and reliability can be prevented from lowering due to temperature rise.

In the above-described embodiment, the flexible printed circuit board made of polyimide or polyester is used as the flexible printed circuit board 11.
However, the present invention is not limited to this, and a flexible printed circuit board using another base material or a rigid board whose base material is, for example, glass epoxy or paper phenol may be used. Further, in the above-described embodiment, the surface mount type LED is used as the LED 12, but the LED 12 is not limited to this, and a resin mold type LED using a lead frame may be used. LEDs may be provided.

Further, in the above-described embodiment, the prism array 14 and the prism sheets 16a and 16b are provided with a prism made of acrylic photo-curing resin.
Although it is composed of ET base material, it is not limited to this, and instead of acrylic photocurable resin, polyester, acrylic,
The prisms may be formed of a thermoplastic resin such as PC or polyimide, a thermoplastic resin such as epoxy, or a photocurable resin such as urethane, or acrylic, PET, or polycarbonate without using the photocurable resin. The prism may be formed by injection molding or compression molding from polyolefin resin, nobornene resin, silicone or the like. The prism sheets 16a and 16b may be omitted when the light transmitted through the light diffusing member 14 can provide the required front luminance.

Further, in the above-described embodiment, the prisms of the prism array 14 and the prism sheets 16a and 16b are formed to have a right apex angle, but the present invention is not limited to this, and the apex angle may be smaller. You may As a result, the angle of division of light by the prism array 14 and the prism sheets 16a and 16b becomes larger.

Further, in the above-described embodiment, the reflection sheet having the dielectric multilayer film is used as the reflection sheet 18, but the reflection sheet is not limited to this, and a reflection sheet using a metal film such as silver may be used. It may be used, or a metal thin film of aluminum, silver or the like may be deposited on the inner surface of the recess 13a of the case 13. Further, the reflection sheet 18 may be omitted if the LED 12 has high luminous efficiency or can be driven by a larger driving current.

In the above-described embodiment, the LCD
Although the uniform surface emission for back lighting of the panel has been described, the prism sheets 16a and 16b and the prism array 1 are described.
By changing the distance from 4 as appropriate, the apparent L
By controlling the light emitting position of the ED 12 and changing the pattern formed in the light diffusing member 15, it is possible to emit light from a part or a plurality of positions on the light emitting surface. By combining the light receiving parts with each other, it is possible to use a plurality of LEDs as a color detection sensor utilizing the spectral action of the prism. Further, by arranging a plurality of direct type surface light source devices 10 in a line, it is possible to use as a line light source. For example, a light source for a facsimile machine, a printer, a copier, a back light for a switch, or the like. It can be used as a light source for indoor indirect lighting.

As described above, the direct type surface light source device according to the present invention is used for a backlight of a transmissive or semi-transmissive LCD panel, a facsimile device, an image reading light source such as a copying machine or a scanner, a copying machine, a printer or the like. It can be used as a light source for static elimination when controlling the charge on the photoconductor by light, a light source for interior use, a light source for various guides and instructions.

[0049]

As described above, according to the present invention, a part of the light emitted from each LED enters the prism array and is diffused in the direction perpendicular to the prism direction of the prism array. Then, the light diffused by the prism array is diffused and made uniform when passing through the light diffusing member, and is further condensed by the prism sheet and emitted upward. As a result, the light emitted from each LED is reduced in influence of the bright line in the optical axis direction due to the directivity of each LED by the prism array and the light diffusing member, and a more uniform and high-output surface light source is obtained. Will be done. Therefore, even if the distance between each LED and the light diffusing member is relatively short, the light emitted from each LED reaches the light diffusing member after being diffused by the prism array, so that a uniform surface light source is obtained as a whole. Will be done. In this way, according to the present invention, it is possible to provide an extremely excellent direct type surface light source device that can perform uniform illumination even with a short optical path length with a simple configuration.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a configuration of an embodiment of a direct type surface light source device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of the direct type surface light source device of FIG.

FIG. 3 is an exploded perspective view of the direct type surface light source device of FIG.

4A is a plan view showing a prism array in the direct type surface light source device of FIG. 1, FIG. 4B is a side view, and FIG.

FIG. 5 is a schematic cross-sectional view showing the configuration of an example of a conventional sidelight type surface light source device.

FIG. 6 is a schematic cross-sectional view showing the configuration of an example of a conventional direct type surface light source device.

[Explanation of symbols]

10 Direct type surface light source device 11 Flexible printed circuit board 12 LED 13 cases 13a concave part 14 Prism array 14a prism 15 Light diffusion member 16a, 16b Prism sheet 17 cover 18 Reflective sheet

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Claims (6)

[Claims] 1. A direct type surface light source device comprising: at least one LED mounted on a printed circuit board so that an optical axis thereof is vertical; and a light diffusing member spaced above the LED. A direct type surface light source device comprising a prism array having a prism on a surface facing the LED between the LED and the light diffusion member. 2. In the prism array, the distance d from the LED is L with respect to the distance L from the LED to the light diffusing member.
The direct type surface light source device according to claim 1, wherein the direct type surface light source device is arranged at a position of / 2 or less. 3. The direct type surface light source device according to claim 1, further comprising a light diffusion surface around the LED for diffusing light from the LED upward. 4. The direct type surface light source device according to claim 1, further comprising a reflection portion around the LED, the reflection portion reflecting the light from the LED upward. . 5. The direct type surface light source device according to claim 4, wherein the reflecting portion is a sheet-like reflecting member. 6. The direct type surface light source device according to claim 4, wherein the reflection portion is a reflection film provided on an inner surface of a case surrounding the LED.