CN1211675C - Hollow surface illuminator - Google Patents

Abstract

A light-conducting unit (6) which can effectively balance the light-leaking effect and the light-propagation effect of the prismatic films (1, 2) forming the light-conducting space (3), and satisfy the requirements to reduce the weight of the unit is disclosed. A light-conducting unit (6) comprising the first prismatic film (1) and the second prismatic film (2), each having two major surfaces, one of which is a prismatic surface, and the other of which is a flat surface, said prismatic surface carrying prisms arranged substantially parallel to each other, wherein said two prismatic films (1, 2) are arranged so that the first edges (11, 21) of said prismatic films (1, 2) are positioned to form an opening (30), a light-conducting space (3) is formed between said prismatic films (1, 2), and the height of said light-conducting space (3) does not substantially increase from said opening (30) to the remote edges (12, 22) of the prismatic films (1, 2) opposing said opening (30), and the major surface of said first prismatic film (1) which faces outside said light-conducting space (3) is a light-emitting surface, and the arrangement of the both prismatic films (1, 2) and the directions of the prisms of the both prismatic films (1, 2) in relation to the incident direction of light (40) are defined under the specific conditions.

Description

light guide unit

technical field

The present invention relates to a light guide unit used as a surface light source for a backlight of a liquid crystal display or an outdoor signboard, or as an internal or external lighting device. The light guide unit of the present invention can be used to replace the traditional light guide plate, and because it has a hollow light guide space inside, it can reduce the weight of the light guide unit and therefore the surface light source.

Background technique

As shown in FIG. 1 , a conventional surface light source emits light using a solid light guide plate 10 that receives light from a point source or a line source (ie, a lamp in FIG. 1 ). The light guide plate is usually made of a polymer material such as acrylic resin. The light emitted from the light source enters the light guide plate through the light incident edge (light incident side), and is allowed to emit from one of the main surfaces of the light guide plate, and the light passes through the plate from the light incident edge toward the light incident edge. The opposite far edge of the plate is propagated. This achieves surface light emission.

The propagation of light through the light guide plate utilizes total internal reflection of light at the interface between the air and the light guide plate, which is due to the difference in refractive index between the air and the light guide plate (polymer material). Such light guide plates are an essential part of backlighting surface light sources for liquid crystal displays. For example, Japanese Unexamined Patent Application A-11-142845 discloses such a light guide plate and a backlight including the light guide plate.

However, when a solid light guide plate is used, it becomes difficult to reduce the weight of the surface light source. For example, with the enlargement of liquid crystal display screens, the area of the light guide plate (light emitting area) and consequently the thickness of the surface light source have gradually increased. Therefore, the increase in the weight of the light guide plate makes it very difficult to reduce the weight of the surface light source, thereby making it difficult to reduce the weight of the liquid crystal display. Even in the case of small liquid crystal displays, it is highly required to reduce the weight of surface light sources, for example, terminals such as portable personal computers, mobile phones, PHS, etc.

Therefore, it has been proposed to use a hollow light guide unit instead of a solid light guide plate. For example, a hollow light guide unit is known, which includes a light emitting plate and a back plate, which are arranged parallel to each other to form a hollow light guide space, and two back plates respectively arranged on the light emitting plate and towards the inside of the light guide space Prismatic film on the surface.

A dichroic film is a well-known optical element, meaning a light-transmitting film, whose one main surface is flat and whose other main surface carries a plurality of prisms (so-called parallel prisms) arranged lengthwise parallel to each other. Such light transfer films are typically placed between the light guide plate and the object to be illuminated (eg, a liquid crystal display, etc.).

In order to emit light from the light guide unit, generally, a linear light source (for example, a fluorescent tube, etc.) is placed along an opening formed at one end of the above light guide space, and light is radiated in the light guide space through the opening. The above-mentioned opening is formed by arranging the above-mentioned pair of light-splitting films substantially parallel to each other with a gap between them. The pair of dichroic films are usually arranged with their planar surfaces parallel to each other.

Such a light guide unit has a first opening formed at one end of the unit, and a second opening formed at the other end opposite to the end (an end farthest from the end), and two light sources are placed in each opening, Light is radiated into the lightguide space. Since the paired light-splitting films are arranged parallel to each other, the height of the light guide space (along the thickness direction), that is, the dimension perpendicular to the light-emitting surface, is from the first opening at one end to the second opening at the farthest end of the section. The opening is substantially unchanged.

The inventors of the present invention proposed an embodiment including such a hollow light guide unit and a surface light source including the light guide unit and a light source in JP-A-6-180552. Before the invention of JP-A-6-180552, other embodiments of light guiding units were known.

In other embodiments of the light guide unit, (i) the arrangement direction of the dichroic film prisms on the light emitting plate is parallel to the direction of light emitted by the light source, and the surface of the dichroic film carrying the parallel prisms is arranged to face the outside of the light guide space. In addition, (ii) the direction of the dichroic film prism on the back plate is also parallel to the direction of the light emitted by the light source, and the surface of the dichroic film is arranged to face the outside of the light guide space. In the case of a surface light source including such a light guide unit, the illuminance of light emitted from the light emitting surface tends to decrease as the distance from the light source increases. Therefore, additional optical elements must be added to correct for this reduction in illumination. Such an additional optical element is a so-called extractor, which has saw-tooth-shaped projections for reflection, the distance between which increases with the distance from the light source. Such extractors are usually placed on the planar surface of the beam-splitting film on the backplane side.

The present inventor proposes a kind of improved light guide unit in JA-A-6-180552, to provide a cheap light guide unit and surface light source, it does not need any extractor and surface light source, therefore, can design very easily And production.

That is to say, the proposed hollow light guide unit includes a pair of dichroic films, which are fixed in corresponding positions so that they are arranged in a specific three-dimensional structure, wherein (1) the ribs of a dichroic film used as a light emitting plane The prismatic surface is arranged in such a way that the direction of the prisms of the dichroic film is perpendicular to the direction of light emitted from the light source, and the prismatic surface faces the inside of the light guiding space. In addition, (II) other dichroic films are arranged such that the direction of the prisms of the other dichroic films is parallel to the direction of light emitted from the light source, and the prism-shaped surface faces the inside of the light guide space. Thereby, the illuminance on the light emitting surface becomes uniform without using an extractor.

With such a light guide unit as described above, part of the light emitted from the light source is reflected by the dichroic film, and the remaining part of the light passes through the dichroic film on the light emitting side and is emitted from the light emitting surface (light leakage). The light reflected by the light-splitting film is emitted from the light-emitting surface, or, through repeated reflection and transmission by the light-splitting films in the light guide space, propagates from an end close to the light source to an end farthest from the light source. That said, the balance between light leakage and light propagation is important. If the light leakage effect is too strong, the amount of light to be propagated decreases, and thus, the uniformity of light emission tends to deteriorate. An increase in the light leakage effect results in an increase in the brightness of the illumination.

Therefore, according to the purpose of the light guide unit (that is, the surface light source), the scale and the like, in order to balance light leakage and light transmission, and to achieve the required brightness and uniformity of emitted light, the structure of the light guide unit must be optimized, for example , optimize the three-dimensional structure of the two spectroscopic films and combine the shapes of the prisms, or select and use optical components such as extractors.

Contents of the invention

As mentioned above, the hollow light guide unit comprising a pair of light splitting films arranged parallel to each other and fixed in a specific structure can reduce the weight of the unit itself, the surface light source and a device (for example, a liquid crystal display, etc.) comprising the surface light source .

However, it is difficult to produce the above-mentioned conventional light guide unit having a relatively thin thickness. With the enlargement of the screen of the liquid crystal display, further reduction in the thickness of the liquid crystal display is highly demanded. In addition, it is also required to reduce the thickness of the above-mentioned portable terminal.

To meet these requirements, it is necessary to reduce the thickness of the light guide unit (ie, the thickness or height of the light guide space) to 30 mm or less, preferably to 20 mm or less.

The reduction of the thickness of the light guide unit means the reduction of the height of the light guide space, and the height of the light guide space is the dimension of the space perpendicular to the light propagation direction. On the other hand, the area of the light emitting surface (ie, the light propagation distance) does not decrease significantly with decreasing cell thickness. The present inventors have conducted further studies after the above proposal in JP-A-6-180552 was made. As a result, it was found that a large amount of light can leak near the edge where the light source is placed, or, when the height of the light guide space is relatively low, almost all of the light amount can propagate to the farthest end without leakage. Therefore, in order to easily realize the thinning of the cell thickness, it is necessary to balance the light leakage effect and the light propagation effect more effectively than before. However, using an additional optical element such as an extractor complicates the structure of the unit and makes it difficult to reduce the weight of the unit.

The present invention provides a light-weight light guide unit, which can effectively balance the light leakage effect and light propagation effect of the light splitting film constituting the light guide space, and can meet the requirement of reducing the weight of the unit.

According to a first aspect of the present invention, there is provided a light guide unit, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening, a light-guiding space, it starts from the opening, is continuous between the light-splitting films, and the height of the light-guiding space from the opening to the far edge of the opening is equal or reduced , and the main surface of the first light-splitting film facing the outside of the light-guiding space is a light-emitting surface to emit light propagating from the opening to the light-guiding space, wherein the first light-splitting film The prismatic surface is placed towards the outside of the light guide space, and the direction of the prisms of the first dichroic film is not parallel to the direction of the light.

According to a second aspect of the present invention, there is provided a light guide unit, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening, a light-guiding space, it starts from the opening, is continuous between the light-splitting films, and the height of the light-guiding space from the opening to the far edge of the opening is equal or reduced , and the main surface of the first light-splitting film facing the outside of the light-guiding space is a light-emitting surface to emit light propagating from the opening to the light-guiding space, wherein the first light-splitting film The prismatic surface is placed towards the outside of the light guide space, and the direction of the prisms of the first dichroic film is parallel to the incident direction of the light; the arrangement direction of the prisms of the second dichroic film not parallel to the direction of the ray.

According to a third aspect of the present invention, a light guide unit is provided, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening and a light guide space, it is continuous from the opening, formed between the light splitting films, and the main surface of the first light splitting film facing the outside of the light guide space is a light emitting surface to emit light propagating from the opening to the light guiding space, characterized in that the prismatic surface of the first light splitting film is placed toward the outside of the light guiding space, and the first light splitting film The direction of the prism is parallel to the direction of the light, the prismatic surface of the second dichroic film is placed towards the outside of the light guide space, and the direction of the prism of the second dichroic film is also parallel to the direction of the light The directions of the light rays are parallel; the reason is that the two light splitting films are arranged in such a way that the height of the light guide space decreases from the opening to the far edge relative to the opening.

According to a fourth aspect of the present invention, there is provided a light guide unit, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening, a light-guiding space, it starts from the opening, is continuous between the light-splitting films, and the height of the light-guiding space from the opening to the far edge of the opening is equal or reduced . And the main surface of the first light-splitting film facing the outside of the light-guiding space is a light-emitting surface to emit light propagating from the opening to the light-guiding space, wherein all the light-splitting films of the first light-splitting film The prismatic surface is placed towards the inner side of the light guiding space, and the prismatic surface of the second light splitting film is placed towards the outer side of the light guiding space.

According to a fifth aspect of the present invention, there is provided a light guide unit, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening, a light-guiding space, it starts from the opening, is continuous between the light-splitting films, and the height of the light-guiding space from the opening to the far edge of the opening is equal or reduced . And the main surface of the first light-splitting film facing the outside of the light-guiding space is a light-emitting surface to emit light propagating from the opening to the light-guiding space, wherein all the light-splitting films of the first light-splitting film The prismatic surface is placed towards the inner side of the light guiding space, and the prismatic surface of the second light splitting film is also placed towards the inner side of the light guiding space.

According to a sixth aspect of the present invention, there is provided a light guide unit, which includes a first light-splitting film and a second light-splitting film, each light-splitting film has two main surfaces, one of which is a prismatic surface, and the prismatic surface carries multiple prisms, which are arranged substantially parallel to each other along the length direction of the prisms, wherein the two dichroic films are arranged such that the first edges of the dichroic films are arranged substantially parallel to each other, leaving a gap between them Next gap to form an opening, a light-guiding space, it starts from the opening, is continuous between the light-splitting films, and the height of the light-guiding space from the opening to the far edge of the opening is equal or reduced . And the main surface of the first light-splitting film facing the outside of the light-guiding space is a light-emitting surface to emit light propagating from the opening to the light-guiding space, wherein all the light-splitting films of the first light-splitting film The prismatic surface is placed towards the inside of the light guide space, and the direction of the prisms of the first dichroic film is perpendicular to the direction of the light, at the vertex angle of the prisms of the first dichroic film smaller than the apex angle of the prism of the second dichroic film.

Description of drawings

Fig. 1 is a cross-sectional view of a traditional surface light source;

Figure 2 shows the optical function depending on the structure of the beam splitting film; and

3 is a cross-sectional view of a surface light source including a preferred example of a light guide unit according to the present invention.

Detailed ways

The function of the light splitting film is to totally reflect light internally, or to allow light to refract and pass between them according to the vertex angle of the prism, the surface where the light enters, the incident angle of the light, etc. Such an optical function of the dichroic film can be explained with reference to FIG. 2 .

The beam-splitting film shown has a plurality of parallel prisms of the same shape and size on its prismatic surface, arranged along the length of the prisms. The example of FIG. 2 qualitatively illustrates the optical function of a dichroic film comprising prisms with an apex angle of 90° and a base angle of 45°.

When the light is radiated on the spectroscopic film at the center of the sphere in Figure 2(a) or 2(b), the light reaching the film through the A region is totally reflected, while the light reaching the film through other regions propagates in the film and is refracted. The refracted light can either return to the inside of the sphere or pass through the membrane, and then, depending on the angle or number of refractions, is emitted (leaks out) from the surface opposite the incident surface. That is, depending on the light's angle of incidence, the light is either totally internally reflected and propagated to the farthest end, or, refracted and allowed to pass through the membrane, and then selectively emitted. The shape and size of the region A vary with the characteristics of the incident surface facing the inside of the light guide space (ie, whether the incident surface is a prismatic surface or a flat surface), or the shape and size of the prism. Therefore, an effective combination of a pair of dichroic films having such optical functions can adjust the balance between the light leakage effect and the light propagation effect.

According to the present invention, the thickness of the unit can be easily reduced by properly selecting the three-dimensional structure of the dichroic film and the shape of the combined prism, and balancing the light leakage effect and the light propagation effect. The combination of the three-dimensional structure of the spectroscopic film and the shape of the prism should be optimized, which is summarized as follows:

(a) the orientation of the prismatic surfaces combining the two dichroic films, i.e., facing the inside or outside of the light guiding space;

(b) The direction of the prisms of the two dichroic films, that is, the angle between the direction of the prisms and the incident direction of the light emitted from the light source; when the direction of the prisms is parallel to the direction of the light emitted from the light source, the angle is 0° , when the direction of the prism is perpendicular to the direction of light emitted from the light source, the angle is 90°;

(c) the apex angles of the prisms that combine the two dichroic films; that is, the dichroic films may have the same apex angle, or they may have different apex angles;

(d) The planes of the combined two dichroic films; that is, their plane surfaces are parallel to each other, or not parallel to each other. In the case of non-parallel, the two light-splitting films are arranged such that the height of the light-guiding space decreases from the opening formed at one end to the farthest end from the opening. In this case, the shape of the cross-section of the light guiding space in a plane along the light incident direction is in the form of a wedge.

Referring now to FIG. 3, a preferred embodiment of the light guide space according to the present invention, which is assembled by effectively combining the three-dimensional structure of the light splitting film and the shape of the prism, will be described.

Fig. 3 is a vertical cross-sectional view of a surface light source (60) and a light source (4) comprising the light guide unit (1) of the present invention. The figure is a cross-sectional view of the surface light source in a plane perpendicular to the light emitting surface along the incident direction of light (40) from the light source (4) to the light guiding space (3).

In the embodiment of Fig. 3, two light-splitting films (1, 2) are arranged to form a light guide unit (6), and the light-splitting films (1, 2) included in the unit leave a distance to provide a hollow space between the two. Light guide space (3). In addition, one edge (11, 12) of the light splitting film (1, 2) is positioned to be parallel to each other, and a gap is left between the two to form an opening (30), and the opening (30) and the light guiding space (3) are continuously.

The light source (4) is arranged near the opening (30), so that it can effectively illuminate the inside of the light guide space (3), and forms a surface light source (60) together with the light guide unit (6). In the embodiment of Figure 3, the reflective plane (41) is placed such that it partially covers the illuminated surface of the light source (4). The reflective plane (41) effectively prevents illumination of light in other directions than the light guide space. Generally speaking, the reflective film (5) is arranged on the back surface of the second dichroic film (2), that is, the outer surface opposite to the surface facing the inside of the light guide space, so as to increase the light emitting surface of the first dichroic film (1). illuminance, i.e., the upper surface in Figure 3.

When the light guide unit as shown in the embodiment of Fig. 3 is assembled, the cross section of the light guide space (3) preferably has a wedge shape. That is to say, the plane surfaces of the light-splitting films (1, 2) are not parallel to each other, and the two light-splitting films are arranged in this way: the height of the light-guiding space (3) is from the first edge (11, 12) (where the light source ( 4)) The opening (30) is lowered to the farthest edge (12, 22).

In the first embodiment of the present invention, the first of the two dichroic films (which is placed on the light emitting surface side) should be placed such that its prismatic surface faces the outside of the light guiding space. In this case, the direction of the prisms of the first dichroic film should be parallel to the direction of light. Thereby, the light leakage effect and the light propagation effect are well balanced, so the thickness of the light guiding unit can be easily reduced.

In this embodiment, the three-dimensional arrangement of the second dichroic film and the shape of the prisms are not limited. However, the direction of the prisms of the second dichroic film is preferably not parallel to the direction of the prisms of the first dichroic film, especially, the angle between the directions of the two prisms is preferably in the range between 40° and 90° . Therefore, even when the light guiding space has a height of 30 mm or less, especially, 20 mm or less, the light leakage effect and the light propagation effect are very easily balanced.

When the included angle between the two directions of the prism is equal to or close to 0°, the apex angle of the prism of the first dichroic film is preferably in the range between 80° and 95°, while the angle of the prism of the second dichroic film The top angle is preferably in the range between 65° and 80°. Therefore, even when the light guiding space has a height of 30 mm or less, the light leakage effect and the light propagation effect are very easily balanced.

In the above-mentioned first embodiment, the included angle between the direction of the prism of the first dichroic film and the direction of the light is not equal to 0, that is, the two directions are not parallel to each other. Generally, such angles are in the range between 40° and 90°.

In the second embodiment of the present invention, the prismatic surface of the first dichroic film is placed facing the outside of the light guiding space, and the direction of the prisms of the first dichroic film is parallel to the direction of light. In this embodiment, the three-dimensional structure of the second dichroic film is formed as follows. That is to say, the direction of the prisms of the second dichroic film is not parallel to the direction of the light. Thereby, the light leakage effect and the light propagation effect are well balanced, so the thickness of the light guiding unit can be easily reduced. The included angle between the direction of the prism of the second light splitting film and the direction of the light is not equal to 0, that is, the two directions are not parallel to each other. Generally, such angles are in the range between 40° and 90°.

In the third embodiment of the present invention, the prismatic surface of the first dichroic film is placed to face the outside of the light guide space, the direction of the prisms of the first dichroic film is parallel to the direction of light, and the direction of the prisms of the second dichroic film is also parallel to the light direction The direction of light is parallel. In this embodiment, the relative structures of the two light splitting films are formed as follows. That is, as shown in Figure 3, two dichroic films are arranged such that the height (dimension in thickness direction) of the light guiding space decreases from the opening (30) at the first edge of the film to the edge furthest from the opening. The prismatic surface of the second light splitting film is placed facing the outside of the light guiding space. Thereby, the light leakage effect and the light propagation effect are well balanced, and thus the thickness of the light guiding unit can be easily reduced.

Generally speaking, the structure in which the prismatic surface of the first light-splitting film is placed facing the outside of the light guide space, and the directions of the prisms of the two light-splitting films are all parallel to the direction of light is unfavorable for increasing the light leakage effect . However, such disadvantages can be avoided when the two dichroic films are oppositely arranged as described above, and the vertical section of the light guiding space is in the form of a wedge.

Compared with the above-mentioned embodiments, the prismatic surface of the first dichroic film can be placed to face the inner side of the light guiding space. In this case, the three-dimensional structure of the second dichroic film and the shape of the prisms may be formed as follows.

In the fourth embodiment of the present invention, the prismatic surface of the first dichroic film is placed facing the inner side of the light guiding space, and the prismatic surface of the second dichroic film is placed facing the outer side of the light guiding space. Thereby, the light leakage effect and the light propagation effect are well balanced, and thus the thickness of the light guiding unit can be easily reduced.

In this embodiment, the direction of the prisms of the second dichroic film is preferably substantially parallel to the direction of light. Therefore, even when the light guiding space has a height of 30 mm or less, the light leakage effect and the light propagation effect are very easily balanced.

In this fourth embodiment, the angle between the prism direction of the first dichroic film and the light direction is preferably in the range between 40° and 90°. Therefore, even when the light guiding space has a height of 20 mm or less, the light leakage effect and the light propagation effect are very easily balanced.

In the fifth embodiment of the present invention, the prismatic surface of the first light splitting film is placed facing the inside of the light guiding space, and the prismatic surface of the second light splitting film is also placed facing the inside of the light guiding space. In this embodiment, the direction of the prisms of the first dichroic film is not perpendicular to the direction of light. In this case, the angle between the direction of the prisms of the first dichroic film and the direction of the light is preferably in the range between 30° and 60°. Therefore, even when the light guiding space has a height of 30mm or less, the light leakage effect and the light propagation effect are very easily balanced. From such a viewpoint, the angle between the direction of the prisms of the first dichroic film and the direction of light is preferably within a range between 40° and 50°.

In this fifth embodiment, the direction of the prisms of the second dichroic film is substantially parallel to the direction in which light is incident. The included angle between the direction of the prisms of the first dichroic film and the direction of light is preferably in the range between 30° and 60°, and the direction of the prisms of the first dichroic film is substantially parallel to the direction of light. Therefore, even when the light guiding space has a height of 20 mm or less, the light leakage effect and the light propagation effect are very easily balanced.

In the sixth embodiment of the present invention, the prismatic surface of the first dichroic film is placed facing the inside of the light guide space, and the prismatic surface of the second dichroic film is also placed facing the inside of the light guide space, and the direction of the prisms of the first dichroic film is vertical in the direction of light. In this case, the apex angles of the prisms of the first dichroic film are smaller than the apex angles of the prisms of the second dichroic film. Thus, the light leakage effect and the light propagation effect can be well balanced.

Also in this embodiment, the direction of the prisms of the second dichroic film is preferably substantially parallel to the direction of light. Therefore, even when the light guiding space has a height of 30mm or less, the light leakage effect and the light propagation effect are very easily balanced.

In this sixth embodiment, the apex angles of the prisms of the first dichroic film are preferably in the range between 65° and 80°, and the apex angles of the prisms of the second dichroic film are preferably between 80° and 95°. in the range between.

In the spectroscopic film used in the present invention, a plurality of prisms extend in the longitudinal direction of the prisms and are parallel to each other. The shape of the apex of each prism may be polygonal or circular.

In order to effectively improve the effect of light propagation, the apex of the prism is preferably a polygon with a specific vertex angle. In the case of a polygonal apex, its apex angle is usually from 60° to 100°, preferably from 65° to 95°, most preferably from 70° to 90°.

The light splitting film used in the present invention is made of a polymer having a light transmittance of at least 80%, preferably at least 85%, most preferably at least 90%. The light transmittance here is the total light transmittance measured according to JIS K7105.

The production of the beam splitting film can utilize a mold with a specific shape and structure corresponding to the shape and structure of the prism to shape the polymer. The polymer used to form the spectroscopic film is preferably a highly transparent polymer having a refractive index of 1.4 to 1.9, for example, acrylic polymer, epoxy modified acrylic polymer, polycarbonate, and the like.

The size of the dichroic film is not limited as long as the effect of the present invention is not impaired. Generally, the thickness of the dichroic film (the distance from the flat surface to the top of the prism) is from 50 μm to 2 mm.

The pitch of the prisms (distance between adjacent tops) is usually 0.020 to 0.5mm, preferably 0.022 to 0.3mm, and the height of the prisms (height from the bottom between adjacent prisms and tops) is usually 0.01 to 1 mm, preferably 0.011 to 0.6 mm.

Commercially available specific examples of the spectroscopic film used according to the present invention include "BEF(R) series", "IDF(R) series" and "TRAF(R)" (all of which are available from 3M, USA).

According to the present invention, the surface light source can be assembled like the conventional surface light source mentioned above. That is to say, the components of the surface light source may be the same as those of the conventional surface light source except for the light guide unit.

For example, as a light source, a light source having a conventional shape such as a linear (rod-shaped) light source, a spherical light source, etc. may be used. For example, fluorescent tubes, cold cathode ray tubes, light emitting diodes, etc. can be used.

In addition to the light source disposed near the first opening formed at one edge of the dichroic film, an additional light source may be disposed near the second opening formed at the farthest edge of the dichroic film. In this case, the height of the light-guiding space does not change substantially from the first opening to the second opening at the edge furthest from the first opening. That is to say, the planar surfaces of the two dichroic films are substantially parallel to each other.

When the surface light source is assembled, a frame or box surrounding the light guide space is provided so that light does not leak from any part except the light emitting surface of the light splitting film. In addition, an opaque film such as a reflective film may be provided on the outer surface of the second dichroic film (relative to the light guiding space).

As mentioned above, one of the main surfaces of the first dichroic film, that is, the outer surface with respect to the light guiding space, is a light emitting surface.

When the surface and the back surface of the light guide unit are reversed such that the first dichroic film is processed as the second dichroic film and vice versa, some light guide units may have the structures included in the above-described embodiments. In this case, the outer surface of the second dichroic film may be used as a light emitting surface.

The area of the light emitting surface is not limited. In the example of liquid crystal displays, the light guide unit according to the invention can be used in liquid crystal displays with screens of about 2 cm ² on the one hand, and liquid crystal displays with large screens of about 1 m ² in the other hand.

As described above, according to the present invention, the height of the light guiding space can be reduced, and the thickness of the light guiding unit and the thickness of the surface light source can also be reduced. The height of the light guiding space is generally 1 to 30 mm, preferably 2 to 20 mm.

Here, the height of the light guiding space is the distance between the facing main surfaces of the two dichroic films measured at the opening formed at the first edge of the film (where the light source is disposed). When the prismatic surface of one light-splitting film faces the inner side of the light-guiding space, the height of the light-guiding space is the distance between the top of the prism of one light-splitting film and the main surface of the other light-splitting film. When the prismatic surfaces of the two light-splitting films face the inner side of the light-guiding space, the height of the light-guiding space is the distance from the top of the prism of one light-splitting film to the top of the prism of the other light-splitting film.

example

Light guide units of Examples and Comparative Examples were fabricated as described below. Planar dimensions of the spectroscopic film used in each example are as follows. The plane size of the spectroscopic film used in each example was 40 mm×40 mm.

BEFII: Dichroic film (brightness enhancement film) "BEF(R) II, 90/50" is commercially available from 3M Company in the United States. This film carries a plurality of parallel prisms on its prismatic surface, and the widthwise cross-section of each prism is an isosceles triangle with an apex angle of 90°. The distance between the tops of adjacent prisms (prism pitch) was 50 μm, and the thickness of the dichroic film (distance from the flat surface of the film to the tops of the prisms) was 155 μm.

TRAF: The spectroscopic film "TRAF(R) II" is commercially available from 3M Company, USA. This film carries a plurality of parallel prisms on its prismatic surface, and the widthwise cross-section of each prism is an isosceles triangle with an apex angle of 70°. The prism pitch was 31 μm, and the thickness of the dichroic film was 145 μm.

IDF20: The light-splitting film "IDF(R)" is commercially available from 3M Company in the United States. This film carried a plurality of parallel prisms on its prismatic surface, and the widthwise cross-section of each prism was a triangle with an apex angle of 70.7°, one base angle of 77.6° and the other base angle of 31.7°. The prism pitch was 50 μm, and the thickness of the dichroic film was 150 μm.

When using such a dichroic film having an asymmetric cross-section along the width direction of the prisms, when the arrangement direction of the prisms is not parallel to the incident direction of light, either side plane of the prisms can face the light source. The side plane facing the light source can be chosen such that the effects of light leakage and light propagation are well balanced.

In the examples described below, in examples 4, 7, 12, 20 and 24, the dichroic film is arranged such that the side of the prism corresponding to the larger base angle (in the case of IDF20 is a base angle of 77.6°) The plane faces the light source, whereas in Examples 3 and 6, the dichroic film is arranged such that the side planes of the prisms corresponding to the smaller base angle (31.7° base angle in the case of IDF20) face the light source. The surface light sources of Examples 3 and 16 had the same structure except that the side surfaces of the prisms of the first dichroic film facing the light source were different.

Examples 1 to 24

A light guide unit having the structure of Fig. 3 is assembled as follows. Table 1 shows the combination of the type and three-dimensional structure of the spectroscopic film in each example. Hereinafter, referring to Example 1, the production steps of the light guide unit will be described.

At first, BEF II (available from 3M Company) as the first light-splitting film is placed on the light-emitting side so that the prismatic surface faces the outside of the light-guiding space (in Table 1, marked with "O" (outside) ), and BEF II as the second dichroic film is placed on the back surface side, so that the prismatic surface faces the inside of the light guide space (in Table 1, marked with "I" (inside)). An opening is formed at an edge of the two light splitting films. The height of the light guide space measured at this opening is 4 mm. The farthest edges from the openings of the two dichroic films are set as close as possible so that they are almost in contact with each other.

In FIG. 3 , the arrangement direction of the prisms of the first dichroic film is perpendicular to the plane of the paper, while the arrangement direction of the prisms of the second dichroic film is parallel to the plane of the paper. That is to say, the direction of the prisms of the first dichroic film is perpendicular to the incident direction of the light emitted from the light source (marked "H" in Table 1), while the direction of the prisms of the second dichroic film is parallel to the incident direction of the light emitted from the light source direction (marked "V" in Table 1).

The light guide units of other examples were assembled in the same manner as in Example 1, except that the combinations of the types of light-splitting films and the three-dimensional structures shown in Table 1 were used.

After each light guide unit of examples is assembled, the situation to the propagation and leakage of light is observed as follows:

The light guide unit is set in a dark room, and four point light sources (LEDs) are arranged in parallel with the opening and emit light. Then, observe the radiation and propagation of light from the light-emitting surface. In all instances, four bright streams of light emanating from the LEDs traveled continuously on the light emitting surface (the major surface of the beam splitting film) from the first edge with the light source to the edge furthest from the light source. That is to say, with the light guide unit of the present invention, the light propagation effect and the light leakage effect can be balanced in the thin light guide space, and according to the brightness of the light source (illumination) etc., the required brightness and uniformity of light emission can be achieved .

Comparative example 1

The light guide unit of this comparative example was assembled in the same manner as in Example 1, except that two transparent acrylic resin films (no prisms on both surfaces) were used at the positions of the two dichroic films.

With the light guide unit of this comparative example, the conditions of light propagation and light leakage were observed in the same manner as in the examples. Then, the area near the first edge (the light source) is brightly illuminated, while the area near the furthest edge is not illuminated at all. That is, since the film has no prisms, the effects of light leakage and light propagation cannot be balanced.

Comparative example 2

In addition to the three-dimensional structure of the first dichroic film so that the prismatic surface faces outward, and the direction of the prism is parallel to the incident direction of light (marked with "VO"), the three-dimensional structure of the second dichroic film makes the prismatic surface face outward, and the prism The light guide unit of this comparative example was assembled in the same manner as Example 1, except that the direction of the light was parallel to the direction of light (marked with "VI").

With the light guide unit of this comparative example, the conditions of light propagation and light leakage were observed in the same manner as in the examples. Then, the area near the first edge (the light source) is brightly illuminated, while the area near the furthest edge is not illuminated at all. That is to say, even if the same dichroic film is used, but their three-dimensional structure is not correct, the light leakage effect and the light propagation effect cannot be balanced.

〔Table 1〕 instance number The first light splitting film Second light splitting film 1 BEF II HO BEF II VO 2 TRAF HO BEF II VO 3 IDF 20 HO BEF II VO 4 IDF 20 HO BEF II VO 5 BEF II HO BEF II VI 6 TRAF HO VEF II VI 7 BEF II HO IDF 20 HI 8 BEF II HO BEF II 45I 9 BEF II 450 BEF II VI 10 BEF II 450 BEF II HI 11 BEF II VO BEF II 45I 12 BEF II VO IDF 20 HO 13 BEF II VO BEF II HI 14 TRAF VO BEF II HI 15 IDF 20 VO BEF II HI 16 BEF II BO IDF 20 HI 17 BEF II VO BEF II VO 18 BEF II HI BEF II VO 19 TRAF HI BEF II VO 20 IDF 20 HI BEF II VO twenty one BEF II 45I BEF II VO twenty two BEF II 45I BEF II VI twenty three TRAF HI BEF II VI twenty four IDF 20 HI BEF II VI

Note:

H: The direction of the prism perpendicular to the direction in which light is emitted from the light source.

V: The direction of the prism parallel to the incident direction of the light emitted from the light source.

45: The direction of the prism is inclined by 45° with respect to the incident direction of the light emitted from the light source.

I: The prismatic surface faces the inner side of the light guiding space.

O: The prismatic surface faces the outside of the light guiding space.

Claims (6)

1. an optical guide unit (6), it comprises one first spectro-film (1) and one second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) arrange like this, that is, and first edge (11 of described spectro-film, 21) be provided with parallel to each other basically, and between them, stay a gap forming an opening, and a photoconduction space, it is continuous from the described opening that is formed between the described spectro-film, and the equal or reduction of the height in the described photoconduction space at the edge, distant place of described spectro-film from described opening to relative this described opening, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, to launch from the light of described opening to described photoconduction spatial transmission, and the described prismatic surfaces of described first spectro-film (1) is placed towards the outside in described photoconduction space, and the direction of the direction of the described prism of described first spectro-film (1) and described light is not parallel.

2. an optical guide unit (6), it comprises first spectro-film (1) and second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) arrange like this, that is, and first edge (11 of described spectro-film, 21) be provided with parallel to each other basically, and between them, stay a gap forming an opening, and a photoconduction space, it is continuous from the described opening that is formed between the described spectro-film, and the equal or reduction of the height in the described photoconduction space at the edge, distant place of described spectro-film from described opening to relative this described opening, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, to launch from the light of described opening to described photoconduction spatial transmission, and the described prismatic surfaces of described first spectro-film (1) is placed towards the outside in described photoconduction space, and the direction of the described prism of described first spectro-film (1) is parallel with the direction of described light, and

The direction of the described prism of described second spectro-film (2) is not parallel with the direction of described light.

3. an optical guide unit (6), it comprises first spectro-film (1) and second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) are arranged like this, that is, first edge (11,21) of described spectro-film is provided with basically parallel to each other, and between them, staying a gap to form an opening and a photoconduction space, it is continuous from the described opening that is formed between the described spectro-film, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, to launch from the light of described opening to described photoconduction spatial transmission, the described prismatic surfaces of described first spectro-film (1) is placed towards the outside in described photoconduction space, and the direction of the described prism of described first spectro-film (1) is parallel with the direction of described light, the described prismatic surfaces of described second spectro-film (2) is placed towards the outside in described photoconduction space, and the direction of the described prism of described second spectro-film (2) is parallel with the direction of described light, and

Described two spectro-films (1,2) are arranged like this, that is, the edge, distant place of the described spectro-film of the height in described photoconduction space from described opening to relative this opening reduces.

4. an optical guide unit (6), it comprises first spectro-film (1) and second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) arrange like this, that is, and first edge (11 of described spectro-film, 21) be provided with parallel to each other basically, and between them, stay a gap forming an opening, and a photoconduction space, it is continuous from the described opening that is formed between the described spectro-film, equal or the reduction of the height in the described photoconduction space at the edge, distant place of spectro-film from described opening to described relatively opening, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, to launch from the light of described opening to described photoconduction spatial transmission, the described prismatic surfaces of described first spectro-film (1) is placed towards the inboard in described photoconduction space, and the described prismatic surfaces of described second spectro-film (2) is placed towards the outside in described photoconduction space.

5. an optical guide unit (6), it comprises first spectro-film (1) and second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) arrange like this, that is, and first edge (11 of described spectro-film, 21) be provided with parallel to each other basically, and between them, stay a gap forming an opening, and a photoconduction space, it is continuous from the described opening that is formed between the described spectro-film, equal or the reduction of the height in the described photoconduction space at the edge, distant place of spectro-film from described opening to described relatively opening, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, to launch from the light of described opening to described photoconduction spatial transmission, and the described prismatic surfaces of described first spectro-film (1) is placed towards the inboard in described photoconduction space, and the described prismatic surfaces of described second spectro-film (2) is also placed towards the inboard in described photoconduction space, and

The orientation of the described prism of described first spectro-film (1) is not orthogonal to the incident direction of described light.

6. an optical guide unit (6), it comprises first spectro-film (1) and second spectro-film (2), each spectro-film has two first type surfaces, one of them is a prismatic surfaces, described prismatic surfaces is carried a plurality of prisms, and they are arranged mutually substantially parallel along the length direction of prism

Wherein, described two spectro-films (1,2) arrange like this, that is, all first edges (11,21) of described spectro-film are provided with basically parallel to each other, and between them, stay a gap to form an opening, be formed between described all spectro-films from the continuous photoconduction space of described opening, the equal or reduction of the height in the described photoconduction space at edge, distant place from described opening to described relatively opening, and

First type surface towards described first spectro-film (1) in the described photoconduction space outside is a light emission surface, with emission from the light of described opening to described photoconduction spatial transmission,

It is characterized in that, the described prismatic surfaces of described first spectro-film (1) is placed towards the inboard in described photoconduction space, and the described prismatic surfaces of described second spectro-film (2) is placed towards the inboard in described photoconduction space, and the orientation of the described prism of described first spectro-film (1) is perpendicular to the described incident direction of described light, and

The drift angle of described prism that is described first spectro-film (1) is less than the drift angle of the described prism of described second spectro-film (2).

Images