JP4599979B2 - Lighting device - Google Patents

Description

  The present invention relates to an illumination device including a light source and a planar light guide plate that guides light incident from the light source and emits the guided light from a light exit surface.

  Due to individual differences of light sources such as LEDs (color and brightness variations), illumination light emitted from the illumination device has variations in chromaticity and luminance. In particular, in an illumination device equipped with a plurality of light sources, chromaticity and luminance unevenness may occur. In addition, selecting and using only light sources having appropriate chromaticity and brightness from light sources having individual differences wastes resources and makes the lighting device expensive.

  In addition, although the point which forms a diffraction grating on a light-guide plate is already well-known in patent document 1, said problem has remained by using only a diffraction grating.

Patent documents are shown below.
Japanese Patent No. 2865618

  The present invention has been made to satisfy the above-mentioned demands, compensates for individual differences in light sources (variation in color and brightness), and compensates for individual differences in chromaticity and / or luminance of light emitted as illumination light. To provide a lighting device with low quality and stable quality. It is another object of the present invention to provide a lighting device that can effectively use light sources having individual differences, does not waste resources, and is suitable for low-cost manufacturing.

In order to achieve the above object, the invention of claim 1 is characterized in that a plurality of upper light sources and a plurality of planar light guides light incident from the light sources and emits the guided light from a light exit surface. In a lighting device including a light guide plate, a light emission optical element made of a diffraction grating is arranged on a light emission surface or a surface opposite to the light emission surface, and the wavelength distribution and / or luminance of light incident on the light guide plate from the light source In response to the,
The spatial frequency distribution and / or diffraction efficiency of the diffraction grating is compensated so that light emitted from a plurality of light guide plates corresponding to a plurality of light sources falls within a predetermined chromaticity and / or luminance range. An illumination device characterized by using an optical element for light emission is used .

  Therefore, the spatial frequency distribution and diffraction efficiency of the diffraction grating formed on the light guide plate compensate for the wavelength distribution and brightness variation of light incident on the light guide plate from the light source, and within a predetermined chromaticity and brightness range. It is possible to simply emit the illumination light, and to provide a lighting device with stable quality. Further, it is possible to effectively use light sources having individual differences, and to manufacture lighting devices at low cost without wasting resources.

  Furthermore, the light guided in the light guide plate along the average light guide direction is diffracted at a significantly different angle from the totally 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. Since the light can be emitted, a lighting device with high light use efficiency can be easily realized with a simple configuration under conditions suitable for lighting such as an LCD panel. At this time, it is not necessary to use a special optical film or the like, and the illumination device can be realized with a small number of member configurations, and the angle range of the emitted light can be appropriately designed by the function of the diffraction grating. Furthermore, the structure of the diffraction grating on the light guide plate is because the optical element for emission is composed of a diffraction grating, and the structure is extremely small, and can be easily formed in any region by a fine processing technique. It is possible to optimize the arrangement and to construct a light guide plate having a very uniform emission light distribution.

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Further, according to the present invention, a plurality of light sources having chromaticity / brightness variations can be used in a single lighting device, and a plurality of light guide plates can be used regardless of the chromaticity / brightness variations of the light sources. The light emitted from the light source can have substantially the same chromaticity and luminance, and an illuminating device that emits illumination light having uniform chromaticity and luminance within the emission surface can be obtained.

In order to achieve the above object, according to a second aspect of the present invention, in the lighting device of the first aspect, the chromaticity and / or luminance of light emitted from the light source in a plurality of pairs of the light source and the light guide plate. Includes the light source larger than the predetermined chromaticity and / or luminance range. Further, by effectively utilizing light sources having individual differences, it is possible to manufacture a lighting device at low cost without wasting resources.

  Therefore, light sources having large variations in chromaticity and luminance can be used, and light emitted from a plurality of light guide plates has almost the same chromaticity and luminance regardless of variations in chromaticity and luminance of the light sources. Thus, an illuminating device that emits illumination light having uniform chromaticity and luminance within the emission surface can be obtained. Further, by effectively using light sources having individual differences, it is possible to manufacture a lighting device at low cost without wasting resources.

  An object of the present invention is to provide a stable lighting device that compensates for individual differences (color and brightness variations) of light sources and has little individual difference in chromaticity and / or luminance of light emitted as illumination light. In addition, it is possible to effectively utilize light sources having individual differences, adapt to low-cost manufacturing without wasting resources.

  Embodiments of the present invention will be described below with reference to the drawings.

  That is, 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 diffracts the light exit surface or the surface facing the light exit surface. Transmitted diffracted light and / or reflected diffracted light is generated by the light emitting optical element formed of a grating, and is emitted from the light guide plate. Here, the light guided in the light guide plate along the average light guide direction is diffracted by the function of the diffraction grating to an angle significantly different from the total reflection light by the function of the diffraction grating. 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. Both the directly emitted light from the diffraction grating and the light that is diffracted by the diffraction grating and then reflected by the reflecting sheet to become the emitted light are both 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.

  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 emitting optical element 38. 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 improve efficiency. 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 d = mλ / (sin θi−sin θR). Is done. 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.

  From this equation, it is clear that the wavelength of light diffracted in a specific direction can be selected by the spatial frequency of the diffraction grating. The diffraction efficiency refers to the ratio of the diffracted light to the incident light. In the present invention, it refers to the diffraction efficiency in a broad sense, and the phase modulation amount of the diffraction grating (for example, depth and refractive index in the case of a relief type diffraction grating). In the case of the modulation type, it varies depending on the difference in refractive index and thickness) and the area where the diffraction grating is formed. Therefore, in the present invention, by appropriately designing the spatial frequency and diffraction efficiency for a specific wavelength for each light guide plate, the emission direction and intensity of the wavelength light are controlled according to the wavelength distribution and intensity of the light source. In addition, the light emitted from the light guide plate can be within a predetermined chromaticity and luminance range. That is, it is possible to realize an illuminating device that compensates for variations in chromaticity and luminance of the light source by the function of the diffraction grating formed on the light guide plate and emits illumination light having stable chromaticity and luminance.

  In general, light sources such as LEDs have large variations in chromaticity and luminance at the time of manufacturing, and are classified into groups having appropriate chromaticity and luminance after manufacturing. In the illuminating device of the present invention, as shown in FIG. 3, for each of these sorted light sources, a light guide plate prepared in advance corresponding to each group is combined, so that stable chromaticity / An illumination device that emits illumination light having luminance can be manufactured. In addition, the manufactured light source can be used without waste, and the lighting device can be manufactured at low cost, and resources can be effectively used.

  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 exits from the light exit surface 28 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. 4 (a) has only the function of bending the light being guided, and the curved diffraction grating pattern as shown in FIG. 4 (b) 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 is configured to effectively act on light satisfying the total reflection condition when the average light guide direction F and the average grating vector direction v are matched. Can do. 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.

  The emission optical element may be formed on the entire surface of the light guide plate. However, as the emission optical element, a diffraction grating formed in each cell-like region may be used, and a large number of cells may be arranged on the light guide plate. FIG. 5 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 decrease in the amount of emitted light due to a decrease in the amount of light guided in the light guide plate along the average light guide direction F is determined by 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.

  Here, the outer shape of the cell 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 also contributes to more effective suppression of unnecessary coloring in the emitted light by combining the two diffracted lights having the above-described contradictory spectral effects.

  Further, when the cell arrangement interval is set to 100 μm or less, the resolution is lower than that of the human eye under general observation conditions, and the size of the cell is sufficiently small even when the light exit surface 28 of such an illumination device is visually observed. Since a sufficient number of cells can be arranged per unit area, it can be observed as a surface that emits uniform emitted 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. For this reason, 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 emission surface 28 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.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the gist of the present invention. For example, not only the arrangement density of the diffraction grating is changed, but also the cross-sectional shape of the diffraction grating (blazed grating, rectangle, sinusoidal shape, etc.) is appropriately selected according to the design.

  The present invention can be applied to an illumination device including an LED, another light source, and a planar light guide plate that guides light incident from the light source and emits the guided light from a light exit surface. .

FIG. 1 is a perspective view of an illuminating device including a planar light guide plate that guides light incident from a light source and emits the guided light from a light exit surface. FIG. 2 is a cross-sectional view showing a state in which the emission optical element 38 in the illumination device of FIG. 1 emits light in the light guide plate. FIG. 3 is a perspective view of an illuminating device including a plurality of pairs, each having a planar light guide plate that guides light incident from a light source and emits the guided light from a light exit surface. Is. It is explanatory drawing which shows the example of the diffraction grating used as an optical element for injection | emission. FIG. 5 is a plan view when 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. FIG. 6 is an enlarged view of the outer shape of the cell. FIG. 7 is a perspective view showing an example in which a display device is configured by combining the illumination device of FIG. 1 with an LCD panel.

DESCRIPTION OF SYMBOLS 10 ... Light guide plate 12 ... Light source 14 ... Illumination device 18 ... Transmission type liquid crystal panel 24 ... Display device 28 ... Light emission surface 32 ... Reflective sheet 38 ... For emission Optical element 56 ... Emission light from light guide plate 58 ... Display light F ... Average light guide direction V ... Lattice vector direction

Claims (2)

In an illuminating device comprising a plurality of light sources and a plurality of planar light guide plates for guiding light incident from the light sources and emitting the guided light from a light exit surface,
A light emitting optical element comprising a diffraction grating is arranged on the light emitting surface or the surface facing the light emitting surface,
Depending on the wavelength distribution and / or brightness of light incident on the light guide plate from the light source,
The spatial frequency distribution and / or diffraction efficiency of the diffraction grating is compensated so that light emitted from a plurality of light guide plates corresponding to a plurality of light sources falls within a predetermined chromaticity and / or luminance range. An illumination device using a light emitting optical element. The plurality of pairs of the light source and the light guide plate includes the light source in which chromaticity and / or luminance of light emitted from the light source is larger than the predetermined chromaticity and / or luminance range. Item 2. The lighting device according to Item 1 .

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