WO2012039432A1

WO2012039432A1 - Optical sheet, area light source device, and transmission image display device

Info

Publication number: WO2012039432A1
Application number: PCT/JP2011/071510
Authority: WO
Inventors: 尚規奥; 武志川上
Original assignee: 住友化学株式会社
Priority date: 2010-09-21
Filing date: 2011-09-21
Publication date: 2012-03-29
Also published as: JP2012069282A; TW201222030A

Abstract

Provided are an optical sheet capable of dispersing light with sufficient uniformity from a point light source, an area light source device, and a transmission image display device. An optical sheet (30) formed from a light-transmitting translucent resin and taking the shape of a sheet, is provided in a structure comprising: a lateral surface (33) into which light emitted from a point light source (22) enters; and an emitting surface (31) which is formed in a direction intersecting the lateral surface, and which emits a plane of light. On the lateral surface (33), protruding parts (35) extending out in the thickness direction of the sheet are positioned in alignment with the longitudinal direction Y of the lateral surface (33).

Description

Optical sheet, surface light source device, and transmissive image display device

The present invention relates to an optical sheet, a surface light source device, and a transmissive image display device that can emit light incident from a plurality of discrete point light sources arranged in a planar shape.
It is.

As a direct type image display device which is an example of a transmissive image display device, a device in which a light source is disposed on the back side of a transmissive image display unit is widely used. Examples of the transmissive image display unit include a liquid crystal display panel in which linear polarizing plates are arranged on both surfaces of a liquid crystal cell. As the light source, a plurality of linear light sources such as a straight tube type cold cathode ray tube are arranged in parallel with each other.

In such a direct type image display device, it is desirable that the light from the light source can be uniformly dispersed to uniformly illuminate the transmissive image display unit. For this reason, between the light source and the transmissive image display unit, from the light source side. A light control plate such as a single light diffusing plate having a function of changing the direction of the incident light and emitting it from the opposite transmission type image display unit side is used (for example, see Patent Document 1). .

In recent years, transmissive image display devices have become thinner, and surface light source devices in which light sources are arranged on the edge side have been developed. In order to spread light emitted from the edge portion over the entire screen instead of the conventional light diffusion plate. Light guide plates are starting to be used. In addition, as an environmental measure, mercury (Hg) is not included, and the use of light emitting diodes (LEDs) is increasing as a light source with low power consumption.

The light guide plate is mainly made of highly light-transmitting resin, and the light of the LED arranged at the end of the light guide plate can be uniformly spread over the entire screen by the reflection and scattering effects in the light guide plate. It has been demanded.

In addition, as an edge light type planar light source with uniform brightness using the light from the LED light source effectively, it is a plate-shaped member made of a translucent member. One having an optical plate is known (for example, see Patent Document 2). In addition, as an edge light type light guide plate, one having an uneven surface that disperses light from an LED light source in the thickness direction is provided on an incident surface (see, for example, Patent Document 3).

JP-A-7-198913 JP 2001-342263 A JP 2008-10291 A

However, in the light control plate used in the conventional surface light source device, the light from the point light source cannot be made sufficiently uniform, particularly in the vicinity of the end of the light control plate, between adjacent light sources. There was a problem that an area with insufficient brightness occurred.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical sheet, a surface light source device, and a transmissive image display device that can more uniformly disperse light from a point light source and reduce an area where brightness is insufficient. And

The present invention is an optical sheet formed from a light-transmitting resin, and is formed in a side surface serving as an incident surface on which light emitted from a point light source is incident, and in a direction intersecting the side surface. An optical sheet is provided that has a light exit surface and a plurality of convex portions that extend in the thickness direction of the sheet and are arranged in the longitudinal direction of the light entrance surface on the side surface that serves as the light entrance surface. To do.

In this configuration, light from a point light source arranged to face the side surface of the optical sheet is incident from the side surface of the optical sheet, and planar light is emitted from an output surface formed in a direction intersecting the side surface. be able to. In addition, light incident from the side surface serving as the incident surface of the optical sheet is provided on the incident surface of the optical sheet by a convex portion that extends in the thickness direction of the sheet and is arranged in the longitudinal direction of the incident surface. In the longitudinal direction of the incident surface, it is spread over a wider range. Thereby, the area | region where the brightness of the edge part (side surface vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient.

Here, it is preferable that the convex portions have a prism shape that is arranged at a pitch of 0.03 mm to 10.0 mm in the longitudinal direction of the incident surface and has an apex angle of 90 ° to 150 °. Thereby, the light incident from the incident surface can be suitably diffused in the longitudinal direction of the incident surface. A more preferable range of the apex angle of the prism shape is a range of 110 ° to 140 °.

Moreover, this invention provides a surface light source device provided with said optical sheet and the some point light source discretely arrange | positioned in the longitudinal direction of an incident surface facing the side surface used as the incident surface of an optical sheet. .

In this configuration, since the optical sheet is provided, the light from the point light source arranged to face the side surface of the optical sheet is incident from the side surface of the optical sheet, and is formed in a direction intersecting with the side surface. Planar light can be emitted from the emission surface. In addition, light incident from the side surface serving as the incident surface of the optical sheet is provided on the incident surface of the optical sheet by a convex portion that extends in the thickness direction of the sheet and is arranged in the longitudinal direction of the incident surface. In the longitudinal direction of the incident surface, it is spread over a wider range. Thereby, the area | region where the brightness of the edge part (side surface vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient.

Further, the point light source is preferably an LED light source in which the normal direction of the point light source is maximum luminous intensity and the half value width of the luminous intensity distribution is 40 ° or more and 80 ° or less.

The present invention also includes the above-described surface light source device and a transmissive image display unit that is disposed so as to face the emission surface of the surface light source device and displays an image by being irradiated with light emitted from the surface light source device. A transmissive image display device is provided.

In this configuration, since the surface light source device is provided, light from a point light source arranged to face the side surface of the optical sheet is incident from the side surface of the optical sheet, and is formed in a direction intersecting with the side surface. Planar light can be emitted from the exit surface. In addition, light incident from the side surface serving as the incident surface of the optical sheet is provided on the incident surface of the optical sheet by a convex portion that extends in the thickness direction of the sheet and is arranged in the longitudinal direction of the incident surface. In the longitudinal direction of the incident surface, it is spread over a wider range. Thereby, the area | region where the brightness of the edge part (side surface vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient. In such a transmission-type image display device, light from a point light source can be sufficiently uniformly dispersed to form planar light, and transmission can be performed by the uniformly dispersed planar light. The mold image display unit can be illuminated.

According to the present invention, an optical sheet, a surface light source device, and a transmissive image capable of uniformly dispersing light from a point light source incident from a side surface serving as an incident surface in a longitudinal direction of the side surface serving as an incident surface. A display device can be provided.

It is sectional drawing which shows typically the structure of one Embodiment of the transmissive image display apparatus which concerns on this invention. It is an enlarged plan view which shows the edge part of the light-guide plate in FIG. It is a perspective view which shows the structure of one Embodiment of the light-guide plate which concerns on this invention. It is an enlarged plan view which expands and shows the prism shape formed in the edge part of the light-guide plate shown in FIG. It is a graph which shows an example of the light emission distribution of a LED light source. It is a top view which shows the positional relationship of a prism shape, LED light source, and a luminance value measurement point. It is a top view which shows the positional relationship of the concave lens which concerns on Example 6, LED light source, and a luminance value measurement point.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent element, and the overlapping description is abbreviate | omitted. The dimensional ratios in the drawings do not necessarily match those described.

FIG. 1 is a cross-sectional view schematically showing a configuration of an embodiment of a transmissive image display device according to the present invention. FIG. 1 shows the transmissive image display device 1 in an exploded manner.

(Transparent image display device)
The transmissive image display device 1 includes a transmissive image display unit 10 and a surface light source device 20 disposed on the back side of the transmissive image display unit 10 in FIG. In the following description, as shown in FIG. 1, the arrangement direction of the surface light source device 20 and the transmissive image display unit 10 is referred to as a Z direction (plate thickness direction), which is two directions orthogonal to the Z direction and orthogonal to each other. Two directions are referred to as an X direction and a Y direction.

Examples of the transmissive image display unit 10 include a liquid crystal display panel in which linearly

polarizing plates

12 and 12 are arranged on both surfaces of a liquid crystal cell 11. In this case, the transmissive image display device 1 is a liquid crystal display device (for example, a liquid crystal television). As the liquid crystal cell 11 and the

polarizing plates

12 and 12, those used in the transmissive image display device 1 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 TFT type and STN type. The transmissive image display unit 10 is disposed so as to face the emission surface 31 of the surface light source device 20 and displays an image by being irradiated with light emitted from the surface light source device 20.

(Surface light source device)
The surface light source device 20 includes a light guide plate (optical sheet) 30 and an LED light source (point light source) 22 arranged to face the side surface 33 of the light guide plate 30.

(light source)
The LED light source 22 functions as a point light source of the surface light source device 20 and is disposed to face the side surfaces 33, 33 extending in the Y-axis direction of the light guide plate 30, as shown in FIG. . The plurality of LED light sources 22 are discretely arranged along the longitudinal direction (Y-axis direction) of the side surface 33. The arrangement interval of the LED light sources 22 is normally 5 mm to 150 mm.

The LED light source 22 may be a white LED, and a plurality of LEDs may be arranged in one place to constitute one light source unit. For example, as one light source unit, LEDs of three colors different in red, green, and blue may be arranged close to each other. And the light source unit which has several LED is discretely arrange | positioned according to the arrangement | positioning direction mentioned above. In such a case, it is preferable that different LEDs are arranged as close as possible.

As the LED light source, those having various light emission distributions can be used. However, the luminous intensity in the normal direction (X-axis direction) of the LED light source is maximum, and the half-value width of the luminous intensity distribution is 40 ° or more and 80 ° or less. Those having a certain light emission distribution are preferred. Specific examples of the LED light source type include a Lambertian type, a shell type, and a side emission type.

FIG. 5 is a graph showing an example of the light distribution of the LED light source. The relationship between the emission angle φ and the emission light intensity is shown assuming that the emission light intensity in the normal direction of the LED light source (emission angle φ = 0 °) is 1.0 (reference). In the LED light source having the light emission distribution shown in FIG. 5, the half width is about 60 °. In addition, you may use the LED light source which has another light emission distribution.

(Light guide plate)
As shown in FIG. 2, the light guide plate 30 has a rectangular shape, and the size of the plan view shape is selected so as to match the screen size of the target transmissive image display device 10, but is usually 250 mm × 440 mm or more. It is preferably 1020 mm × 1800 mm or less. The planar view shape of the light guide plate 30 is not limited to a rectangle but may be a square, but in the following, it will be described as a rectangle unless otherwise specified.

Here, the rectangle of 250 mm × 440 mm or more means a rectangle having one side of 250 mm or more and the other side of 440 mm or more. Further, the rectangle of 1020 mm × 1800 mm or less means a rectangle having one side of 1020 mm or less and the other side of 1800 mm or less.

The light guide plate 30 is formed of a translucent resin that transmits light and has a plate shape. The light guide plate 30 may be a sheet or a film.

The light guide plate 30 includes a pair of main surfaces (31, 32) facing in the Z-axis direction (thickness direction), a pair of side surfaces 33, 33 facing in the X-axis direction, and a pair of side surfaces 34 facing in the Y-axis direction. 34 is provided.

One main surface (31) of the pair of main surfaces facing in the Z-axis direction functions as an emission surface 31 that emits planar light. The emission surface 31 is disposed on the transmissive image display unit 10 side, and the other main surface (back surface 32) is disposed on the opposite side to the transmissive image display unit 10. In addition, a reflection sheet that reflects light is applied at a position facing the back surface 32.

(Convex part)
Here, a plurality of convex portions 35 that are convex outward in the X-axis direction are formed on the side surface 33. The prism shape 35 extends in the thickness direction (z-axis direction) of the sheet, and a plurality of convex portions 35 are arranged side by side in the longitudinal direction (y-axis direction) of the side surface 33. The plurality of convex portions 35 are arranged in parallel. The plurality of convex portions 35 are preferably arranged at a pitch of 0.03 mm to 10.0 mm in the y-axis direction. In the present embodiment, the distance d1 between the vertices of the convex portion 35 is, for example, 8.5 mm.

Further, as shown in FIG. 4, the convex portion 35 is preferably in a prism shape, and the apex angle (vertical angle) θ of the prism shape is preferably 90 ° or more and 150 ° or less, and 110 °. More preferably, it is 140 ° or less. In the present embodiment, the apex angle θ of the prism shape is, for example, 120 °. The plurality of prism shapes have a function of diffusing light from the LED light source 22 in the longitudinal direction of the side surface 33 (Y-axis direction). For example, as shown in FIG. 4, the LED light source 22 is disposed at a position corresponding to the concave portion between the

convex portions

35 and 35.

(Construction material of light guide plate)
The light guide plate 30 is made of a translucent resin. The translucent resin is a resin that transmits light. The refractive index of the translucent resin is usually 1.49 to 1.59. As the translucent resin used for the light guide plate 30, methacrylic resin is mainly used.

Examples of the methacrylic resin include monomers having methyl methacrylate as a main component. Specifically, the methacrylic resin may be a polymer obtained by polymerizing a monomer containing 50% by mass or more of methyl methacrylate. Further, it may be methyl polymetalate obtained by polymerizing methyl methacrylate alone, or a copolymer of 50% by mass or more of methyl methacrylate and 50% by mass or less of a monomer copolymerizable therewith. May be.

Examples of monomers copolymerizable with methyl methacrylate include ethyl methacrylate, propyl methacrylate, butyl methacrylate, benzyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, bornyl methacrylate, adamantyl methacrylate, methacrylic acid, Methacrylic acid esters such as cyclopentanedienyl acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, bornyl acrylate, adamantyl acrylate, acrylic Acrylic esters such as cyclopentadienyl acid, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride and Its acid anhydride, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, acrylic acid, monoglycerol acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacryl Hydroxyl group-containing monomers such as monoglycerol acid, nitrogen-containing monomers such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, diacetone acrylamide, dimethylaminoethyl methacrylate, allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate And epoxy group-containing monomers, and styrene monomers such as styrene and α-methylstyrene.

The translucent resin is not limited to those described above, and may be other resins such as styrene resin, polyethylene resin, polypropylene resin, cyclic olefin polymer resin, acrylonitrile-butadiene-styrene resin, polyethylene terephthalate resin, Examples include polycarbonate resin.

In applying the light guide plate to a liquid crystal display device, additives such as a light diffusing agent, an ultraviolet absorber, a heat stabilizer, and a photopolymerization stabilizer may be added to the light guide plate.

(Light guide plate forming method)
Examples of the method for forming the light guide plate 30 include extrusion molding, cast molding, and injection molding. The thickness t of the light guide plate is not particularly limited, but is preferably 1.0 mm to 10.0 mm, more preferably 1.5 mm to 8.0 mm, and 2.0 mm to 4. Particularly preferred is 0 mm.

(Formation method of convex part)
A hot press molding method can be applied as a method of forming the convex portion (uneven shape). A convex portion is formed on the side surface 33 of the light guide plate 30 by performing hot press molding using an opposite mold having a shape paired with the convex portion as a plate.

Further, an injection molding method may be applied as a method for manufacturing an optical sheet having a convex portion. In the case of the injection molding method, it is preferable that the inner wall of the injection mold is provided with an opposite mold having a shape paired with the convex portion. In addition, as a method for forming the convex portion, a lens film having the convex portion on the surface thereof is prepared, and the surface opposite to the convex portion is connected to the side surface of the light guide plate 30 through an adhesive layer. It is also preferable to bond them together.

If the interval (pitch) between the plurality of convex portions 35 is too small, the processing accuracy may be lowered, and if it is too large, the irregularities due to the convex portions 35 become large and the light guide plate 30 is incorporated into the liquid crystal display device. In addition, the frame portion for concealing the convex portion 35 from the liquid crystal display screen is increased. The pitch of the plurality of convex portions 35 is preferably 0.03 mm to 10 mm.

Examples of the convex portion (concave / convex shape) include the above-mentioned prism shape, lenticular lens shape, trapezoidal shape, rectangular shape, and the like. In particular, in the case of a prism shape, the prism apex angle is preferably 90 ° or more and 150 ° or less, and more preferably 110 ° or more and 140 ° or less.

According to such a light guide plate 30 according to the present embodiment, light from the plurality of LED light sources 22 arranged to face the side surface 33 of the light guide plate 30 is incident from the side surface 33 and orthogonal to the side surface 33 ( Planar light can be emitted from the exit surface 31 that intersects. The light incident from the side surface 33 of the light guide plate 30 is refracted by the convex portion 35 and spread in the y-axis direction. As a result, it is possible to reduce an area where the brightness is insufficient at the end of the light guide plate 30 (in the vicinity of the side surface 33).

Further, according to the surface light source device 20 and the transmissive image display device 1 including the same according to the present embodiment, the light source plate 30 is arranged discretely in the longitudinal direction of the side surface 33 so as to face the side surface 33 serving as the incident surface. The plurality of LED light sources 22 are provided, light from these LED light sources 22 is allowed to enter from the side surface 33, and planar light can be emitted from the emission surface 31 orthogonal to the side surface. The light incident from the side surface 33 of the light guide plate 30 is refracted by the convex portion 35 and spread in the y-axis direction. As a result, the region where the brightness is insufficient at the end of the light guide plate 30 can be reduced. Therefore, the frame part for concealing the region where the brightness is insufficient at the end of the light guide plate 30 so as not to be seen from the display screen can be reduced. The degree of freedom in designing the frame portion that is the peripheral portion of the display screen of the transmissive image display device 1 can be increased.

(Example)
Hereinafter, an example of the optical sheet of the present invention will be described.

An optical sheet according to an example of the present invention and an optical sheet according to a comparative example were prepared, and an evaluation test was performed on them. In Examples 1 to 6 and Comparative Example 1, an optical sheet A was prepared using Sumipec E011 (trade name, manufactured by Sumitomo Chemical Co., Ltd., PMMA) as a translucent resin. The optical sheet A has a thickness of 4 mm, and has a rectangular shape with a length (short side) of 210 mm and a width (long side) of 300 mm.

On the side surface of the long side of the optical sheet A, a plurality of convex portions extending in the thickness direction (z-axis direction) were arranged in the longitudinal direction of the side surface (incident surface). In Examples 1 to 5, the apex angles of the convex portions (prism shape) were 90 °, 120 °, 137 °, 150 °, and 170 °, respectively. In addition, Comparative Example 1 was used in which the convex portion is not formed on the side surface of the optical sheet A (the side surface is a flat surface). In Example 6, a concave lens was provided on the side surface (see FIG. 7). The height of the concave lens was 1.67 mm. In Examples 1-6, irregularities (prism shape, a concave lens) the distance _{P 1} of a 8.5 mm. These uneven shapes were applied by laser processing.

Next, evaluation units were prepared for optical sheets A of Examples 1 to 6 and Comparative Example 1. A white tape (TRUSCO TRT-50 double-sided tape manufactured by TRUSCO) was adhered to the entire back surface 32 of the optical sheet A.

In the evaluation unit, three LED light sources (120 ° Lambertian type; NSSW123B) are arranged in the center of the optical sheet in the thickness direction at intervals of 8.5 mm near the center in the long side direction of the optical sheet and wired to the base did. And the voltage 12V and the electric current 60mA were applied to the LED light source, and the LED light source was turned on. At this time, in the long side direction of the optical sheet, the normal line of the LED light source was arranged so as to correspond to the concave and convex shape.

Then, a luminance meter was installed so that the entire exit surface 31 of the optical sheet A was reflected. The luminance meter was arranged to face the emission surface 31, and the distance from the emission surface 31 to the tip of the luminance meter camera was 800 mm.

FIG. 6 is a plan view showing the positional relationship between the prism shape, the LED light source, and the luminance value measurement point. FIG. 7 is a plan view illustrating a positional relationship among the concave lens, the LED light source, and the luminance value measurement point according to the sixth embodiment. As shown in FIGS. 6 and 7, measurement points P for measuring luminance were provided at equal intervals, and measurement positions were set using XY coordinates. The long side direction of the optical sheet A is set as the Y-axis direction, the short side direction is set as the X-axis direction, 90 points at intervals of 3 mm in the Y-axis direction, 10 points at intervals of 3 mm in the X-axis direction, a total of 900 measurement points P. The luminance value at each measurement point P was measured. The luminance value was collected 5 minutes after the evaluation unit was installed.

For the collected luminance values, an average value of 10 luminance values in the X-axis direction was calculated. The average value of the luminance values in the X-axis direction is within a range of 3 mm (W ₁ = 6 mm) from the light source 22 located in the center among the three LED light sources arranged to both sides in the Y-axis direction (left-right direction in the figure). The maximum value Lmax and the minimum value Lmin were compared. Specifically, D = (Lmin / Lmax) × 100 was calculated as an index D (%) representing the degree of light diffusion. The index D indicates that the larger the numerical value, the more light from the LED light source is spread in the longitudinal direction of the side surface (Y-axis direction in the drawing). Table 1 shows the calculated index D.

As mentioned above, although this invention was concretely demonstrated based on the embodiment, this invention is not limited to the said embodiment. For example, the point light sources may be arranged along one side surface extending in the long side direction of the optical sheet, or may be arranged along one side surface extending in the short side direction. Good. Moreover, the structure by which a point light source is arranged in two side surfaces extended in a long side direction may be sufficient, and the structure arranged in one side surface extended in a short side direction may be sufficient. In addition, it is preferable that the point light source is arrange | positioned in the position corresponding to the recessed part formed between adjacent convex-shaped parts.

Note that the longitudinal direction of the side surface serving as the incident surface is the Y-axis direction at the side surface 35 facing the X-axis direction, and the X-axis direction at the side surface 34 facing the Y-axis direction (see FIG. 3). ).

The convex portions are preferably arranged at equal intervals in the longitudinal direction of the incident surface at a pitch of 0.03 mm to 10.0 mm, but may be arranged at other pitches.

Further, the apex angle of the prism shape which is the convex portion is preferably 90 ° to 150 °, but may be other angles. Further, the convex portion may have a shape other than the prism shape.

The surface light source device, the light control plate unit, and the transmissive image display device of the present invention disperse the light from the point light source incident from the side surface serving as the incident surface sufficiently uniformly in the longitudinal direction of the side surface serving as the incident surface. be able to.

DESCRIPTION OF SYMBOLS 1 ... Transmission type image display apparatus, 10 ... Transmission type image display part, 20 ... Surface light source device, 22 ... LED light source (point light source), 30 ... Light guide plate (optical sheet), 31 ... Output surface, 32 ... Back surface, 33: side surface, 34: side surface, 35: convex portion (prism shape).

Claims

An optical sheet formed from a translucent resin,
A side surface serving as an incident surface on which light emitted from the point light source is incident;
An exit surface that is formed in a direction intersecting with the side surface and emits planar light; and
An optical sheet in which a plurality of convex portions extending in the thickness direction of the sheet and arranged in the longitudinal direction of the incident surface are formed on a side surface serving as the incident surface.
The optical sheet according to claim 1, wherein the convex portions are arranged in a longitudinal direction of the incident surface at a pitch of 0.03 mm to 10.0 mm and have a prism shape having an apex angle of 90 ° to 150 °.
The optical sheet according to claim 1 or 2,
A surface light source device comprising a plurality of point light sources that are opposed to a side surface that is an incident surface of the optical sheet and are discretely arranged in a longitudinal direction of the incident surface.
4. The surface light source device according to claim 3, wherein the point light source is an LED light source in which a normal direction of the point light source is a maximum luminous intensity and a half value width of a luminous intensity distribution is 40 ° or more and 80 ° or less.
A surface light source device according to claim 3 or 4,
A transmission-type image display device comprising: a transmission-type image display unit that is disposed so as to face an emission surface of the surface light source device and displays an image by being irradiated with light emitted from the surface light source device.