JP4600078B2 - Illumination device and liquid crystal display device - Google Patents

Description

The present invention relates to an improvement of a backlight unit (illumination device) in a liquid crystal display device including a built-in light source (backlight) for generating display light.
More specifically, a so-called edge light type backlight having a configuration in which light from a light source disposed on a side surface with respect to a display screen is guided and light is emitted from a light emitting surface to a liquid crystal panel (LCD panel) side. -It is related with the improvement of the planar illuminating device provided with the light-guide plate and the light source in a unit.

Usually, a so-called backlight, which is an illumination light source used on the back surface of a transmissive LCD panel, uses a light guide plate made of a transparent resin in order to uniformly guide light from the light source to the LCD panel.
As shown in FIG. 10, in the illumination device 14 in which the light source 12 is disposed on this type of light guide plate 10, the light that has entered the light guide plate 10 from the end surface 11 of the light guide plate 10 passes through the flat portion of the light guide plate 10. The light guide plate 10 travels in the light guide plate 10 along the average light guide direction F that is the average direction of light guided by the light guide plate 10 while being totally reflected.
10 shows an example in which a linear light source is used as the light source 12, the shape of the light source 12 is not limited to a linear shape, and may be, for example, a dot shape.
Prisms 16 are provided in places on the plane portion of the light guide plate 10, and light hitting the prisms 16 is emitted upward from the light guide plate 10 as indicated by an arrow 56 in the drawing.

  As an example of an illuminating device that does not use a prism as means for taking out light that enters the light guide plate 10 from the end surface 11 of the light guide plate 10 and propagates through the light guide plate 10 from the light exit surface (upper side in the figure). Have proposed a method of diffusing and emitting light by printing scattering dots on the surface of the light guide plate 10 and a method of forming a diffraction grating on the back surface of the light guide plate 10 (Patent Document 1).

In the above light guide plate, it is also an important technical problem to make the light emission amount uniform in the light emission surface corresponding to the display screen of the liquid crystal panel (that is, to make the luminance distribution in the display screen uniform). Yes, as an improved method of forming a diffraction grating on the back of the light guide plate 10,
A light guide plate that diffracts light from a light source incident from at least one end surface of a transparent plate-like body toward the surface of the plate-like body by a diffraction grating provided on the back surface of the plate-like body,
That at least one of the cross-sectional shape of the diffraction grating or the ratio of the grating part width / non-grating part width in the unit width is changed so that the luminance on the surface of the light guide plate increases and becomes uniform. A proposal such as a characteristic light guide plate (Patent Document 2) is also known.
Japanese Patent Laid-Open No. 7-248496 JP-A-9-325218

However, in such an illumination device, it is difficult to increase the rate of converting light incident on the light guide plate from the light source into desired emission light while making the light intensity in the emission surface uniform, and the back of the transmissive LCD panel is difficult. When used as a light or the like, there has been a problem that light utilization efficiency (a ratio of light incident on a light guide plate from a light source that is converted into emitted light in a desired angle range as illumination light) is low.
In particular, it is desirable for a backlight of an LCD panel to emit strong light in the normal direction of the exit surface, but it is extremely difficult to achieve this with only a combination of a light source and a light guide plate.

  In order to convert the light emitted from the light guide plate into an appropriate light distribution, a method of inserting various optical films between the light guide plate and the transmissive display element has been proposed. Another problem arises that the manufacturing cost increases.

  Also, when a prism is used, it is difficult to hide the prism arrangement pattern during visual observation due to the relatively large structure, the light guide plate is thickened by the prism, and the emission angle range of the emitted light. And the intensity of emitted light cannot be controlled freely.

Furthermore, when the light source is installed on the end face of the light guide plate, it is difficult to make the light intensity constant on the side closer to and far from the light source.
In particular, in the case of a spot-like light source or a light source with uneven brightness, the average light guide direction (the light is guided in the light guide plate), which is the average direction in which light travels from the light source side end surface to the end surface far from the light source (Average direction of light) It is more difficult to increase both the uniformity of the distribution of emitted light in the direction orthogonal to F and the light use efficiency.

  The present invention has been made in view of such circumstances, and the object thereof is sufficient in the normal direction of the light exit surface without using an expensive special optical film (such as a prism) other than the light guide plate. An illumination device with a simple configuration capable of obtaining emitted light of light intensity, increasing the light utilization efficiency, increasing the uniformity of the emitted light intensity on the exit surface, and freely controlling the angle range of the emitted light Is to provide.

A lighting device according to claim 1 of the present invention is provided.
A light source;
In an illuminating device including a light guide plate that guides light incident from a light source and emits the guided light from a light exit surface.
A plurality of light emitting optical elements made of diffraction gratings are arranged on both the light emitting surface and the surface facing the light emitting surface.

According to the first aspect of the present invention, the light that is guided in the light guide plate along the average light guide direction is converted into the total reflected light by the synergistic effect of the diffraction gratings arranged on both the light exit surface of the light guide plate and the opposite surface. Diffracted at a significantly different angle from that of the light guide, and in particular, can be emitted toward the normal direction of the light exit surface of the light guide plate, making it easy to create a lighting device with high light utilization efficiency under conditions suitable for lighting such as LCD panels This can be realized with a simple configuration.
In particular, even if the diffraction efficiency of the diffraction grating used as the light emitting element is 50% or less, the light emitting efficiency from the light guide plate is sufficient because it is disposed on the light exit surface of the light guide plate and the opposite surface. Can be high.

Furthermore, it is also possible to give the main optical functions differently to the diffraction gratings arranged and formed on both the light exit surface (front surface) and the opposite surface (back surface) of the light guide plate.
For example, the diffraction grating on the back side functions so as to extract a large amount of light propagating in the light guide plate, and the direction and range of the emitted light and the luminance distribution in the emission surface are controlled by the diffraction grating on the front side. Separation of optical functions such as
In this case, as a matter of course, the structure (shape, cell distribution) and the like of the diffraction grating on the front and back surfaces (front and back surfaces) of the light guide plate differ depending on the required function.

  According to the second aspect of the present invention, the transmitted diffracted light from the diffraction grating on the surface facing the light exit surface of the light guide plate and the reflected diffracted light from the diffraction grating on the light exit surface of the light guide plate are mainly used. From the diffraction grating on the surface facing the light exit surface of the light guide plate and the transmitted diffraction light from the diffraction grating on the light exit surface of the light guide plate The light is emitted from the light guide plate together with the reflected diffracted light, and the light emission efficiency of light desirable as illumination light can be further increased.

  In the invention of claim 3, the light emitting surface and the surface facing the light emitting surface, the light emitting optical element is symmetrical with respect to a plane parallel to the light emitting surface (here, depth or lattice spacing, In the case of a cross-sectional structure including a lattice shape), the light exit surface and the opposite surface act in the same way on the light incident on the side surface of the light guide plate from the light source, so the design of the light guide plate becomes easy, uniform and high efficiency A simple light guide plate. In addition, since only one type of diffraction grating, which is an optical element for emission, can be designed and manufactured, it can be easily realized.

In the invention of claim 4, the light emitting surface and the surface facing the light emitting surface are arranged so that the light emitting optical elements are relatively arranged as viewed from the light emitting surface and the surface facing the light emitting surface. Thus, both sides can be made from the same plate.
That is, by designing and producing a single plate and forming optical elements for injection on both sides of the light guide plate based on this, a highly efficient light guide plate can be produced easily and at low cost.

  In the invention of claim 5, in the invention of claim 4, the arrangement of the optical elements for emission on the light exit surface is asymmetric with the average light guide direction as an axis, so that when viewed from the light exit direction, the light exit surface The entire arrangement of the emission optical elements on the opposite surface does not coincide with each other, and it is possible to realize more uniform emission light within the emission surface of the light guide plate while being easily manufactured.

According to the illuminating device of the present invention, it is not necessary to use a special optical film or the like, and it is possible not only to realize the illuminating device with a small number of member configurations, but also to set the angle range of emitted light by the function of the diffractive optical element. It can be designed as appropriate.
Furthermore, since the emission optical element is composed of a diffractive optical element, the structure is extremely minute and can be easily formed in an arbitrary region by a fine processing technique or the like. The light guide plate having a very uniform emission light distribution can be configured.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view illustrating a configuration example of a lighting device in the lighting device of the present invention.
FIG. 2 is a side view showing a cross section of the illumination device of the present invention.

  In other words, the illumination device according to the present embodiment enters light from the light source into the light guide plate from the side surface, guides the light from the light guide plate while totally reflecting the light, and is disposed on the light emission surface or the surface facing the light emission surface. Transmitted diffracted light and reflected diffracted light are generated by the light emitting optical element comprising the diffraction grating, and the emitted light from the light guide plate, that is, the illumination light can be obtained.

Here, the light guided in the light guide plate along the average light guide direction is diffracted at an angle significantly different from the total reflected light by the function of the diffraction grating, and particularly toward the normal direction of the light exit surface of the light guide plate. Therefore, an illumination device with high light utilization efficiency can be easily realized with a simple configuration under conditions suitable for illumination such as an LCD panel.
As shown in FIGS. 1 and 2, by disposing the reflection sheet on the surface facing the light exit surface of the light guide plate, the main diffracted light component can be effectively used as illumination light.

An example in which a display device is configured in combination with the transmissive liquid crystal display panel 18 is shown in FIG.
In order to diffract the guided light in the normal direction of the exit surface, a diffraction grating with a high spatial frequency is required, but it is not easy to increase the diffraction efficiency of such a diffraction grating.

  However, by forming diffraction gratings on both sides as in the present invention, substantially double the diffraction efficiency can be realized, so that the light use efficiency can be remarkably improved as an illumination device. In addition, by using diffraction gratings on both sides, it is possible to sufficiently control the direction and spread of the emitted light, and light that is desirable as illumination light can be obtained with high efficiency.

FIG. 2 shows how the emission optical element 38 in the illumination device of FIG. 1 emits light in the light guide plate.
When the illumination device of the present invention is used as a backlight of a transmissive LCD panel, the emission optical element 38 can convert the light being guided into light that is emitted in a direction substantially perpendicular to the emission surface. Although desirable, this can be easily realized by using a diffraction grating as the optical element 38 for emission.

  Furthermore, it is possible to set the angle range of the emitted light as appropriate by the function of the diffraction grating, and to realize illumination light having an optimal angular distribution as a display without using any other optical film. Can do.

When a relief type diffraction grating is used as the diffraction grating, it is easy to design a pattern and to form it on a light guide plate.
At this time, since the height (depth) of the structure of the relief type diffraction grating is typically about 0.1 to 1 μm, it is possible to realize the light guide plate 10 that can be regarded as a substantially flat surface with no unnecessary protrusions.
That is, the lighting device can be thinned. Furthermore, it can be integrally formed with the light guide plate 10 and can be manufactured very simply and inexpensively.

Here, the function of the diffraction grating will be discussed in more detail.
Of the light guided through the light guide plate, the light incident on the diffraction grating produces diffracted light, but the normal main diffracted light is first-order diffracted light. In the diffraction grating which is the most basic structure of the diffractive optical element, the relationship between the grating pitch d of the diffraction grating and the emission angle (diffraction angle) θR of the first-order diffracted light is expressed by the following equation (1).
d = mλ / (sin θi−sin θR) (1)
Here, m is the diffraction order, λ is the wavelength of light in the light guide plate, and θi is the regular reflection angle (when the diffraction grating acts during reflection). An almost similar expression is established during transmission.

In order to convert the light traveling in the light guide plate in the average light guide direction into the emitted light, the diffraction grating that works most effectively has a grating vector along the average light guide direction.
That is, by making the grating vector direction and the average light guide direction F substantially the same and appropriately setting the grating pitch d, the light traveling in the average light guide direction F while being totally reflected is diffracted by the diffraction grating at an angle θR, The light is emitted from the light exit surface 26 of the light guide plate 10 outside the total reflection condition. In particular, when θR to 0 °, illumination light is emitted almost perpendicularly to the surface of the light guide plate, and is most preferable as illumination light for a transmissive display.

The diffraction grating not only emits the light guided through the light guide plate as diffracted light, but also can control how the diffracted light spreads (exit angle range).
Specifically, the linear diffraction grating pattern as shown in FIG. 5A has only a function of bending the light being guided, and the curved diffraction grating pattern as shown in FIG. 5B is emitted. The range of diffracted light can be arbitrarily designed according to the pattern.

Here, the diffraction grating pattern on the light guide plate may be configured to effectively act on light satisfying the total reflection condition when the average light guide direction F and the average grating vector direction are matched. it can.
That is, the direction of the emitted light can be greatly different from the light being guided, and the light can be reliably emitted from the light guide plate.

  Furthermore, in the average light guide direction, by giving a width to the spatial frequency of the diffraction grating, the first-order diffracted light emitted from the light guide plate can be emitted within an angle range corresponding to the width of the spatial frequency, Since light is intensively emitted in the set angle range, light can be used efficiently.

Note that it is preferable that each of the emission optical elements uses a diffraction grating formed in a cell-like region, and a large number of cells are arranged on the light guide plate.
FIG. 6 shows an example in which the arrangement density is changed by changing the number of cells arranged per unit area and the size of the cells on the light guide plate.
At this time, the reduction of the emission light due to the decrease in the amount of light guided in the light guide plate along the average light guide direction F indicates the arrangement density of the emission optical elements 38 at each position of the light guide plate, the number of cells arranged, and Since compensation is performed by setting the cell size, light can be emitted uniformly within the emission surface.

In FIG. 6, the upper and lower sides of the figure are asymmetrical. However, when such an arrangement pattern is formed on the light emitting surface of the light guide plate and the surface facing it, the result is as shown in FIG. 7.
In FIG. 7, the injection optical elements arranged on the opposing surface are shown by shading. By forming the asymmetric arrangement on both surfaces of the light guide plate in this way, it is possible to increase the emitted light intensity and easily obtain a uniform emitted light intensity distribution within the emission surface of the light guide plate.

Here, the outer shape of the cell of the optical element for injection may be any of a rectangular shape, a circular shape, and an elliptical shape as shown in FIG.
Moreover, all the cells arranged on the same light guide plate 10 may have the same shape, or a rectangular shape, a circular shape, and an elliptical shape may be mixed.

  As an optimal design example, if the cell has a short shape in the average light guide direction F and a long shape in a direction perpendicular to the average light guide direction F, the emitted light is the same as the average light guide direction F by the diffraction effect due to the cell shape. The angle distribution of the emitted light can be controlled independently of the design of the diffraction grating. The spread of the emitted light contributes to suppressing unnecessary coloring in the diffracted light.

  Further, when the arrangement interval of the emission optical elements is 100 μm or less, the resolution is less than the resolution of the human eye under general observation conditions, and even when the light emission surface 26 of such an illumination device is visually observed, the emission optical elements Is sufficiently small, and a sufficient number of emission optical elements can be arranged per unit area, so that it can be observed as a plane for emitting uniform emission light.

  The diffraction grating has a very small structure, and can easily form a diffractive optical element having an arbitrary optical function in an arbitrary region by using a microfabrication technique. It is possible to construct a light guide plate having a distribution.

In general, the light guide plate has a higher light emission intensity toward the end face closer to the light source (incident side) and a light emission intensity lower toward the end face farther from the light source.
Therefore, by increasing the diffraction efficiency of the diffraction grating as the distance from the light incident side of the light guide plate 10 increases, the ratio of the light emitted from the light guide plate 10 on the incident side where the light intensity is strong decreases, and as the distance from the incident side increases. The ratio can be increased, and light with uniform intensity can be emitted over the entire light exit surface 26 of the light guide plate 10.

Here, when a linear light source disposed substantially parallel to the end face is used as the light source, the average light guide direction F in the light guide plate is a direction substantially orthogonal to the incident end face of the light from the light source.
In addition, when a light source such as a dotted LED arranged on the end face is used as the light source, it tries to guide light in a radial direction centering on the light source, but on average over the entire light guide plate, it is the same as the linear light source The direction substantially perpendicular to the incident end face is the average light guide direction F.

  As described above, the illuminating device of the present invention can obtain illumination light that is emitted substantially in the normal direction of the light emission surface without using a relatively expensive optical sheet such as a prism, and has an emission angle range. It is possible to provide an illumination device that is controlled, can achieve a uniform distribution in the exit surface, has high light utilization efficiency, and can obtain exit light with little color change due to an angle, with a simple configuration.

In addition, the light guide plate 10 may be configured not only to have a flat plate shape (a constant thickness) as shown in FIG. 1 but also to gradually reduce its thickness as it proceeds along the average light guide direction F.
In addition, the present invention does not prevent the use of a cheap and thin structure sheet such as a diffusion sheet, and a diffusion sheet is disposed on the light exit surface side of the light guide plate in order to ensure the uniformity of light within the exit surface. You may do it.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to this structure. Within the scope of the invented technical idea of the scope of claims, a person skilled in the art can conceive of various changes and modifications. The technical scope of the present invention is also applicable to these changes and modifications. It is understood that it belongs to.

The perspective view which shows the structural example of the illuminating device of this invention. The side view which showed the cross section in the illuminating device of this invention. The side view which shows the example at the time of making the optical element for injection | emission in the illuminating device of this invention symmetrical. The side view which shows the mode of the emitted light from general LED. The figure which shows the structural example of the diffraction grating in the illuminating device of this invention. The top view which shows the example of arrangement | positioning of the optical element for injection | emission in the light-guide plate which comprises the illuminating device of this invention. The top view which shows the example at the time of attaching the arrangement | positioning of the optical element for injection shown in FIG. 6 to both surfaces of a light-guide plate. The top view which shows the example of a shape of the optical element for injection | emission in the light-guide plate which comprises the illuminating device of this invention. The perspective view which shows the display apparatus with which the illuminating device of this invention is applied. The perspective view which shows the illuminating device with which the light guide by a prior art is applied. The perspective view which shows the display apparatus with which the illuminating device shown in FIG. 10 is applied.

Explanation of symbols

F ... Average light guide direction 10 ... Light guide plate 12 ... Light source 14 ... Illumination device 16 ... Prism 18 ... Transmission type LCD panel 24 ... Display device 26 ... Light exit surface 28 ... Opposing surface 32 ... Reflector 38 ... Injecting optical element 50 ... light 51 being guided ... diffracted light 56 ... illumination light 58 ... display light

Claims (6)

A light source;
In an illuminating device including a light guide plate that guides light incident from a light source and emits the guided light from a light exit surface.
Consists of a configuration in which a plurality of optical elements for light emission composed of diffraction gratings are arranged on both the light emission surface and the surface facing the light emission surface ,
In the diffraction grating, the average light guide direction and the average diffraction vector direction coincide,
The illumination device according to claim 1, wherein an outer shape of a cell of the optical element for light emission is short in an average light guide direction and long in a direction orthogonal thereto . The lighting device according to claim 1, wherein a light reflective sheet is disposed in the vicinity of a surface facing the light emitting surface. 3. The light emitting surface and the light emitting optical element on the surface facing the light emitting surface have a symmetric lattice structure with respect to a surface parallel to the light emitting surface, respectively. Lighting device. The emission optical elements on the light exit surface and the surface facing the light exit surface are relatively in the same positional relationship when viewed from the light exit surface and the surface facing the light exit surface, respectively. 4. The illumination device according to any one of 3. The illumination device according to claim 4, wherein the arrangement of the emission optical elements on the light exit surface is asymmetric with respect to the average light guide direction. A liquid crystal panel that defines a display image in accordance with translucency / light shielding in pixel units;
A liquid crystal display device comprising at least the illumination device according to claim 1.