WO2014103696A1

WO2014103696A1 - Optical element and lighting device

Info

Publication number: WO2014103696A1
Application number: PCT/JP2013/083046
Authority: WO
Inventors: 三森　満
Original assignee: コニカミノルタ株式会社
Priority date: 2012-12-28
Filing date: 2013-12-10
Publication date: 2014-07-03

Abstract

A lighting device and optical element for a backlight that are suitable for illumination from behind a panel and which can suppress illuminance variation and color variation are provided. Letting the proximity where luminous flux, wherein a color division between a first color and a second color is greatest, is radiated be a boundary (BD), a site having irregularity is provided here. Thus, at the boundary (BD), luminous fluxes for which the colors passing through a first region (AR1) and a second region (AR2) are different from each other are made to cross each other, and along with achieving a mixed color, brightness variations are suppressed by the light ray densities complementing each other.

Description

Optical element and illumination device

The present invention relates to an illuminating device that is installed on the back side of a surface member having a relatively large area and performs backlight illumination so that light passes through the surface member, and an optical element used therefor.

In a conventional large-sized liquid crystal display device, light from a number of cold-cathode tubes arranged on the back side of the liquid crystal panel is guided to the back side of the liquid crystal panel via a diffusion plate, a reflector, etc., and is uniformly used as a backlight. By illuminating, the image was clearly visible. On the other hand, in recent years, an LED light source has been used as a light source of a backlight from the viewpoint of energy saving. Further, from the viewpoint that brightness and darkness can be controlled according to the image displayed on the liquid crystal display device, the LED light source is easy to use, thereby further reducing the power consumption of the liquid crystal display device.

Thus, when using an LED light source as a backlight of a liquid crystal display device, since the chip of the LED light source itself is small, in order to secure a uniform illuminance when trying to arrange such a chip directly on the back side of the liquid crystal panel, It is not realistic because countless chips are required. Therefore, an optical element that converts light emitted from the LED chip into illumination light with uniform illuminance is required. Patent Documents 1 to 3 disclose optical elements for liquid crystal backlights that can convert light from an LED light source into illumination light with as uniform illuminance as possible.

JP 2008-532300 A JP 2006-92983 A JP 2009-44016 JP 2009-192915

By the way, the optical elements disclosed in Patent Documents 1 to 3 have a continuous emission surface shape, and thus the light distribution characteristics of the emitted light are continuous. Here, in order to develop an image displayed on the liquid crystal panel with a natural color, an LED light source that emits white light is generally used for the backlight. As the LED light source that emits white light in this manner, at present, a combination of a blue LED chip that emits a blue light beam and a phosphor that emits yellow light when excited by the blue light beam emitted from the blue LED chip is used. Widely used.

However, as a problem of a white LED light source using a blue LED chip and a phosphor, there is a possibility that color unevenness called a yellow ring centering on the optical axis may occur in white light that has passed through an optical element. When the white light with the generated light is irradiated on the back surface of the liquid crystal panel, there is a risk that natural color development of an image displayed on the liquid crystal panel is impaired. In particular, in an LED light source of a type in which a blue LED chip is sealed with a larger phosphor, a light source that emits light from the entire surface of the phosphor (a light source that emits light from an emission surface of a certain area is referred to as surface emission hereinafter). Light source)), when the vicinity of the blue LED chip near the center of the light emitting surface and the outer periphery of the phosphor sealing material that is the peripheral portion of the light emitting surface are viewed in the vicinity, Since the light beam is intensely yellowish and is enlarged and projected by the optical element, yellow ring is generated. As described above, the reason why the light beam is divided into a strong blue light beam and a strong yellow light beam is that the light beam emitted from the vicinity of the blue LED chip along the optical axis and the light beam emitted toward the periphery differ in the distance passing through the phosphor. It will be. This is because the amount of blue light beam that reacts with the phosphor to become a yellow light beam is different. In addition, when the area of the light emitting surface and the area of the incident surface of the optical element are close to each other, there are light beams with different incident angles emitted from different positions on the light emitting surface even at the same position on the light emitting surface. There is a tendency for color unevenness to occur due to the yellow ring. However, Patent Documents 1 to 3 do not specifically disclose measures for effective suppression of color unevenness.

On the other hand, Patent Document 4 discloses a technique for improving color unevenness by using an incident surface as an optical surface having two different characteristics. However, in the technique of Patent Document 4, since the roughness and characteristics of the optical surface change greatly in the region near the optical axis on the incident surface, color unevenness may be suppressed, but the illuminance (luminance) near the center decreases. May cause uneven illumination. In addition, if the vicinity of the optical axis on the incident surface is made rough, the light distribution of the light that has passed through may not be spread, and the diffusion effect may not be sufficiently obtained.

The present invention has been made in view of the problems of the prior art, and is suitable for illuminating from behind the panel, and provides an illumination device and an optical element for a backlight that can suppress illuminance unevenness and color unevenness. The purpose is to do.

The optical element according to claim 1 is an optical element for a backlight including an incident surface on which a light beam from an LED light source is incident and an output surface that emits the light beam.
The LED light source is a combination of an LED chip and a phosphor having a larger area than the LED chip in the optical axis direction.
The exit surface of the optical element has a boundary that is divided into two regions in the direction perpendicular to the optical axis, a region closer to the optical axis than the boundary is defined as a first region, and a region outside the boundary is defined as a second region. The function defining the exit surface shape of the first region and the function defining the exit surface shape of the second region are discontinuous,
Of the light beams emitted from the LED light source and entering the optical element via the incident surface, at least a light beam emitted from the first region and a light beam emitted from the second region across the boundary are at least An optical element that partially intersects.

¡Backlight optical elements generally have a larger exit surface area than the entrance surface area. Therefore, in order to suppress color unevenness, the shape of the light exit surface can be adjusted more accurately than the case of adjusting the shape of the light entrance surface, and the influence of the shape error can be reduced even if a shape error occurs. . Therefore, in the present invention, the emission surface shape is adjusted. Specifically, in order to suppress color unevenness, the exit surface of the optical element is divided into at least two regions with a boundary in the direction orthogonal to the optical axis, and a region closer to the optical axis than the boundary is defined as a first region. The region outside the boundary is defined as a second region, and the function defining the exit surface shape of the first region and the function defining the exit surface shape of the second region are discontinuous.

When the exit surface is discontinuous at the boundary, the behavior differs between the light beam that has passed through the first region and the light beam that has passed through the second region. This will be described with reference to FIG. FIGS. 1A and 1B are enlarged views showing the vicinity of the boundary BD between the first area AR1 and the second area AR2 which is the emission surface of the optical element. Here, by making the function defining the first area AR1 and the function defining the second area AR2 discontinuous, for example, the example of FIG. 1A is emitted from the center of the light emitting surface of the LED light source. The light ray path of the light beam is shown. In the substantially parallel light ray group L incident from the incident surface, when the light ray that has passed through the first area AR1 is refracted at an angle θ1, the light ray that has passed through the second area AR2 is The light can be refracted at an angle θ2 (> θ1). Thereby, at least a part of the light beam emitted from the first area AR1 and the light beam emitted from the second area AR2 across the boundary BD intersect each other.

On the other hand, the example of FIG. 1B shows a light beam path of a light beam emitted from the vicinity of the light emitting surface of the LED light source. In the light beam group L incident from the incident surface, the light beam L enters the first area AR1 near the boundary BD. The incident light beam L is totally reflected, the light beam density can be locally reduced, and the light beam L incident on the second area AR2 is transmitted. On the other hand, the light beam L ′ incident on the first region AR1 at a position away from the boundary BD is refracted, but this at least partially intersects the light beam L emitted from the second region AR2.

When the LED light source is a combination of an LED chip and a phosphor having a larger area than the LED chip in the optical axis direction, color separation is likely to occur in a ring shape in the light flux that has passed through the optical element, and this is recognized as color unevenness. There is a high possibility of being. This is because, as described above, as the luminous flux is emitted in the peripheral direction, the distance passing through the phosphor becomes longer and the color becomes different. Therefore, in the present invention, for example, the vicinity where the light beam with the most color separation is emitted is defined as a boundary BD, and the function defining the emission surface shape of the first region and the emission surface shape of the second region are defined here. By making the function discontinuous, the light beams having different colors that have passed through the first area AR1 and the second area AR2 are crossed at the boundary BD to promote color mixing and to increase the light density of each other. By complementing each other, uneven illumination is suppressed.

According to a second aspect of the present invention, in the optical element according to the first aspect, the LED light source is configured such that the LED chip that emits a first color light beam and the first color light beam are incident. The phosphor that emits a second color different from the first color is combined.

The present invention is particularly effective when such an LED light source is used.

According to a third aspect of the present invention, there is provided the optical element according to the first or second aspect, wherein the second region shifts to the side away from the LED light source with respect to the first region at the boundary. Is formed.

In the example of FIG. 1A, the light beam Lx (dotted line) emitted from the first area AR1 close to the boundary BD is incident on the step ST formed on the boundary BD, and again passes through the optical element from another location. Since it is emitted, it is not used directly for illumination. On the other hand, in the example of FIG. 1B, a part of the light beams Lx ′ (dotted lines) out of the light beams L ′ emitted from the first area AR1 far from the boundary BD enters the step ST formed on the boundary BD. Again, since it is emitted from another place through the optical element, it is not directly used for illumination. This is called a step vignetting effect. Since there is an inherent limitation in eliminating color unevenness by crossing light beams, the light flux close to the first color or the second color is completely uneven even if color mixing is performed by crossing light beams. Is less likely to be resolved. Therefore, in the present invention, the light flux that cannot completely eliminate the color unevenness even if color mixing is performed is not directly used for illumination due to the vignetting effect of the step, but is emitted from another part of the optical element, and the influence of the color unevenness appears. The light is guided to the non-existing portion, thereby further suppressing the color unevenness of the illumination light. In addition, it can also be made to give a diffused effect to reflected light by making level | step difference ST into a diffused surface.

The optical element according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, the step is 5 μm or more.

When the step is 5 μm or more, an effective vignetting effect can be exhibited and color unevenness can be suppressed. The step is preferably 15 μm or less. If the step becomes too large, the vignetting becomes too large, which may cause uneven illuminance.

The optical element according to claim 5 is the optical element according to any one of claims 1 to 4, wherein the normal line of the first region at a position adjacent to the boundary and the second line at a position adjacent to the boundary. It is characterized in that the normal of the region is different.

Thereby, light beams having different colors that have passed through the first area AR1 and the second area AR2 across the boundary can be refracted in directions close to each other, and color mixing can be promoted.

An optical element according to a sixth aspect of the present invention is the optical element according to any one of the first to fifth aspects, wherein the emission surface has a recess, and the boundary has a diameter of the emission surface with respect to a surface vertex of the emission surface. It is characterized by being formed at a position within ± 10%.

Since the exit surface has a recess, the apex of the surface exists at a position away from the optical axis. For this reason, within ± 10% of the exit surface diameter with respect to the surface apex of the exit surface is a portion that has a large influence on the occurrence of color unevenness in the first place, and ring-shaped unevenness occurs due to the reflection inside the lens and the effect of total reflection. Since this is an easy region, if a step is provided in this region, the vignetting effect can be exhibited with a small step.

According to a seventh aspect of the present invention, in the optical element according to any one of the first to sixth aspects, a third region is formed on the light exit surface with another boundary outside the second region in the direction perpendicular to the optical axis. The function defining the exit surface shape of the second region and the function defining the exit surface shape of the third region are discontinuous.

Thereby, higher quality illumination can be obtained by controlling the light flux that has passed through the second region and the third region.

An optical element according to an eighth aspect of the invention according to the seventh aspect of the invention is the optical element according to the seventh aspect, wherein the third region shifts toward the LED light source closer to the second region with respect to the second region. Is formed.

By providing a step at the boundary between the second region and the third region, an vignetting effect can be exhibited so that an unnecessary light beam is not used for illumination. Preferably, the step between the second region and the third region is 15 μm to 40 μm. If the step becomes too large, the vignetting becomes too large, which may cause uneven illuminance.

The optical element according to claim 9 is characterized in that, in the invention according to

claim

7 or 8, a diffusion surface is formed in the third region.

The illuminance unevenness can be further suppressed by giving a diffusion effect to the emitted light beam by passing through the diffusion surface of the third region.

An optical element according to a tenth aspect is the invention according to any one of the first to ninth aspects, wherein the exit surface has an aspherical shape, and the vicinity of the optical axis of the first region is recessed. And

This can suppress uneven illumination by dispersing the emitted light.

An optical element according to an eleventh aspect is characterized in that, in the invention according to any one of the first to tenth aspects, the incident surface has a concave aspherical shape.

This can suppress uneven illumination by dispersing the emitted light.

The lighting device according to claim 12, wherein an LED chip that emits a light beam of a first color and a second color that is different from the first color by the light beam of the first color emitted from the LED chip. And an optical element according to any one of claims 1 to 11, and an optical element according to any one of claims 1 to 11.

The illumination device according to the present invention has an LED (Light Emitting Diode) light source and an optical element.

Various LED light sources can be used, but it is preferable to use a white LED having a flat light emission surface and emitting white light.

As the white LED, a combination of a blue LED chip and a phosphor such as a YAG phosphor that emits yellow light by a blue light beam emitted from the blue LED chip is preferably used. As the white LED, for example, one described in Japanese Patent Application Laid-Open No. 2008-231218 can be used, but is not limited thereto.

As an example, as shown in FIGS. 2A and 2B, the white LED is disposed on the package substrate PT, and the LED chip CP connected to the electrode ET and the LED chip CP are sealed thereon. The phosphor layer EL having a larger area than the LED chip in the optical axis direction, a tapered reflecting surface MR surrounding the phosphor layer EL, and a case CS supporting the reflecting surface MR. The LED chip CP emits light of a first predetermined wavelength (first color light), and emits blue light in the present embodiment. However, the wavelength of the LED chip of the present invention and the wavelength of the emitted light from the phosphor are not limited, and the wavelength of the emitted light from the LED chip and the wavelength of the emitted light from the phosphor are in a complementary color relationship and the synthesized light is white. Any combination that provides light can be used. The LED chip CP has an area corresponding to a square having a side of 0.5 mm to 1.3 mm, and the phosphor layer EL has an area corresponding to a circle having a diameter of φ2.1 mm to φ3.2 mm, and its thickness. Is preferably 0.5 mm to 1.0 mm.

A known blue LED chip can be used as such an LED chip. As the blue LED chip, any existing one including InxGa1-xN can be used. The emission peak wavelength of the blue LED chip is preferably 440 to 480 nm. In addition, as a form of the LED chip, the LED chip is mounted on the substrate and directly radiated upward or sideward, or the blue LED chip is mounted on a transparent substrate such as a sapphire substrate, and bumps are formed on the surface thereof. Any form of LED chip, such as a so-called flip chip connection type, in which it is formed and turned over and connected to an electrode on a substrate, can be applied.

In FIGS. 2A and 2B, the phosphor layer EL converts the light having the first predetermined wavelength emitted from the LED chip CP into the light having the second predetermined wavelength (light of the second color). Have a body. In an embodiment described later, blue light emitted from the LED chip is converted into yellow light. As a result, white light is emitted from the entire surface of the phosphor layer EL in FIG. That is, the LED light source can be said to be a surface emitting light source having an emission surface having a predetermined area.

The phosphor used for such a phosphor layer uses an oxide or a compound that easily becomes an oxide at a high temperature as a raw material of Y, Gd, Ce, Sm, Al, La and Ga, and converts them into a stoichiometric amount. The raw material is obtained by thoroughly mixing in a theoretical ratio. Alternatively, a coprecipitated oxide obtained by calcining a solution obtained by coprecipitation of oxalic acid with a solution obtained by dissolving a rare earth element of Y, Gd, Ce, and Sm in an acid at a stoichiometric ratio, and aluminum oxide and gallium oxide. Mix to obtain a mixed raw material. An appropriate amount of fluoride such as ammonium fluoride is mixed with this as a flux and pressed to obtain a molded body. The compact can be packed in a crucible and fired in air at a temperature range of 1350 to 1450 ° C. for 2 to 5 hours to obtain a sintered body having the phosphor emission characteristics.

The LED light source is preferably a high-power LED light source. Here, the high-power LED light source can be constituted by an LED having an output of 0.5 watts or more.

The optical element for LED is disposed on the light emission side of the LED light source, and is an incident surface on which light emitted from the LED light source is incident, and a generally convex emission surface that emits light emitted from the LED light source to the outside. Have The entrance surface of the lens and the light emission surface of the LED light source are preferably not in contact with each other, and the space between the entrance surface and the LED light source is preferably filled with air.

The optical element has a leg portion that comes into contact with the substrate provided with the LED light source, and the height of the leg portion is preferably lower than the height of the LED light source. This leg is preferably formed discontinuously in the circumferential direction.

The optical element is preferably made of plastic. As a plastic constituting the optical element, for example, polycarbonate or acrylic can be used. By using polycarbonate or acrylic, it can be manufactured by injection molding, and the manufacturing cost can be greatly reduced.

The diffusion surface may be a mirror surface, including a surface subjected to graining or roughening. Preferably, the surface roughness is Ra 0.2 or more. By setting the surface roughness Ra to a value that is 1/2 or more of the wavelength of the light beam, it is possible to have a diffusion effect. Moreover, generally a mirror surface says Ra0.025 or less.

According to the present invention, it is possible to provide a backlight illumination device and an optical element that are suitable for illuminating from behind the panel and that can suppress uneven illuminance and uneven color.

(A) And (b) is a figure which expands and shows the boundary part vicinity of the 1st area | region and 2nd area | region of an output surface. It is a figure which shows the example of a LED light source, (a) is sectional drawing of a LED light source, (b) is a front view. It is optical axis direction sectional drawing of the illuminating device concerning this Embodiment. 2A and 2B are diagrams illustrating an optical element of Example 1, where FIG. 3A is a view seen from the light exit surface side, FIG. 3B is a cross-sectional view along the optical axis VIB-VIB, and FIG. (D) is the figure seen from the bottom face side. It is a figure which shows the relationship between the radius H and SAG (H) in the entrance plane and exit surface of Example 1. FIG. The relationship between the radius H and θ (H) on the entrance surface and the exit surface of Example 1 is tin. It is a figure which shows the relationship between the radius H and SAG (H) 'in the entrance plane and exit surface of Example 1. FIG. It is a figure which shows the relationship between the radius H and SAG (H) "in the entrance plane and exit surface of Example 1. FIG. (A) is a schematic diagram on the exit surface side of an ideal optical element, (b) is a sectional view in the optical axis direction of the irradiation surface of the ideal optical element, the vertical axis is illuminance, and the horizontal axis is light. It corresponds to the position with reference to the axis. (C) is the schematic diagram by the side of the output surface of the optical element designed by the same idea as Example 1, (d) is the optical axis direction sectional drawing of the irradiation surface in this optical element, A vertical axis | shaft is The illuminance and the horizontal axis correspond to the position relative to the optical axis. (A) superimposes the illuminance curve of the light beam emitted from the vicinity of the center of the light emitting surface of the LED light source of Example 1 and the illuminance curve of the light beam emitted from the peripheral portion of the light emitting surface on the ideal curve, (B) superimposes the illuminance curve of the light beam emitted from the vicinity of the center of the light emitting surface of the LED light source of the comparative example and the illuminance curve of the light beam emitted from the peripheral portion of the light emitting surface on the ideal curve, The vertical axis corresponds to the illuminance, and the horizontal axis corresponds to the position based on the optical axis. The illuminance curves in Example 1 and the comparative example are superimposed on the ideal curve. (A) is an enlarged view showing an optical path near the step ST at the boundary between the second region 1b2 and the third region 1b3 in the example in which the third region 1b3 of the emission surface is a mirror surface, and (b) is It is an enlarged view which shows the optical path at the time of the light beam radiate | emitted from 2nd area | region 1b2 and 3rd area | region 1b3 injecting into the diffuser plate as a to-be-irradiated surface, (c) is diffusing 3rd area | region 1b3 'of an output surface. FIG. 7 is an enlarged view showing an optical path near a step ST ′ at the boundary between the second region 1b2 and the third region 1b3 ′ in the example of the lower surface of the surface PT, and (d) is a diagram illustrating the second region 1b2 and the third region. It is an enlarged view which shows the optical path at the time of the light beam radiate | emitted from 1b3 'injecting into the lower surface of the diffusion plate PT as an irradiated surface. The illuminance curve concerning the light beam emitted from the periphery of the LED light source in Example 1 in which the third region is a mirror surface and a diffusion surface is superimposed on the ideal curve. FIG. 5 is a diagram illustrating an optical element of Example 2, where (a) is a view seen from the exit surface side, (b) is a cross-sectional view along the optical axis direction XIB-XIB, and (c) is a cross-sectional view along the optical axis direction XIC-XIC; (D) is the figure seen from the bottom face side.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 3 is a cross-sectional view in the optical axis direction of the illumination device according to the present embodiment. The backlight illumination device according to the present embodiment includes an optical element 1 and an LED light source 2 formed on a circuit board 3. Although not shown in detail, the LED light source 2 is formed by laminating an LED chip that emits blue light and a yellow phosphor provided on the light emitting side, and has an overall square plate shape. The light emission surface 2a is flat. The LED light source 2 is basically the same as that shown in FIG. 2, where CP is a square with a side of 0.76 mm and an area of about 0.6 mm ² , and EL is a circle with a diameter of φ2.5 mm. The area is about 4.9 mm ² , the area ratio is 1: 8.5, and the thickness of the LED module is 0.8 mm.

The optical element 1 uses polycarbonate or acrylic as plastic. Further, the optical element 1 is disposed on the light emission side of the LED light source 2, and has a concave incident surface 1a on which the light emitted from the LED light source 2 is incident, and the vicinity of the optical axis OA is concave, but is generally convex. And an exit surface 1b that emits light incident from the entrance surface 1a to the outside, a bottom surface 1d that faces the substrate 3, an outer peripheral surface 1f that is a cylindrical surface or a conical surface provided on the outer periphery of the exit surface 1b, Have The outer peripheral surface 1f is a portion where a gate is provided when the LED optical element 1 is injection-molded.

The concave incident surface 1a is a spherical or aspherical refracting surface 1g through which a normal line (coincidence with the optical axis OA) at the center of the light emitting surface 2a of the LED light source 2 passes, and closer to the LED light source 2 than the refracting surface 1g. And a diffusing surface 1h provided outside the direction orthogonal to the optical axis and having a light diffusing action.

The diffusion surface 1h has a tapered shape in which the dimension in the direction perpendicular to the optical axis decreases as the distance from the light emitting surface 2a of the LED light source 2 increases, and the corresponding transfer surface of the mold for molding the LED optical element 1 By increasing the roughness, the surface can be roughened. At this time, by providing a step 1i that faces the LED light source 2 between the diffusion surface side end of the incident surface 1a and the incident surface side end of the diffusion surface 1h, for example, a transfer corresponding to the diffusion surface 1h. When performing shot peening processing or the like to increase the roughness of the surface, it becomes easier to mask the incident surface 1a.

The emission surface 1b is divided into three regions in the present embodiment. More specifically, the first region 1b1 around the optical axis OA is composed of a first region 1b1, an outer second region 1b2, and an outermost third region 1b3. It has become. The function that defines the exit surface shape of the first region 1b1 and the function that defines the exit surface shape of the second region 1b2 are discontinuous. Normals at positions adjacent to the boundary B1 between the first region 1b1 and the second region 1b2 are not parallel to each other. Further, the function that defines the exit surface shape of the second region 1b2 and the function that defines the exit surface shape of the third region 1b3 are discontinuous. Although not visible in FIG. 3, the outer region is shifted upward at the boundary B1, thereby forming a step of 5 μm. Further, the outer region is shifted upward at the boundary B2, thereby forming a step of 20 μm. The third region 1b3 is a rough surface.

The bottom surface 1d can be a rough surface having a diffusing action by increasing the roughness of the corresponding transfer surface of the mold in the same manner as the diffusion surface 1h. The outer peripheral surface 1f can also be a roughened surface having a diffusion action by increasing the roughness of the corresponding transfer surface of the mold.

In the present embodiment, the bottom surface 1d has three leg portions 1j at equal intervals in the circumferential direction, and is attached with the leg portions 1j in contact with the surface of the substrate 3. By disposing the legs 1j discontinuously in the circumferential direction, sealing the LED light source 2 can be suppressed, and the wiring of the LED light source 2 can be pulled out and air permeability can be ensured. The entire leg portion 1j can be made a rough surface having a diffusion action by increasing the roughness of the corresponding transfer surface of the mold, like the diffusion surface 1h.

The height of the leg 1j is lower than the height of the LED light source 2, so that when the LED optical element 1 is attached to the LED light source 2, the bottom surface 1d is lighter than the light emitting surface 2a of the LED light source 2. Arranged on the opposite side to the discharge direction. Thereby, it can suppress that the light discharge | released from the light emission surface 2a wraps around to the bottom face 1d side.

In the present embodiment, the positions of the emission surfaces where the color separation of the first color and the second color is most likely to occur are the boundaries B1 and B2, and the boundaries B1 and B2 are defined by providing discontinuity of the surfaces. Interstitial light beams that have passed through the inner region and the outer region are crossed with each other to promote color mixing, and unevenness in illuminance can be suppressed by complementing each other's light density. Moreover, the uneven color of the illumination light can be further suppressed by the vignetting effect of the steps provided at the boundaries B1 and B2. In addition, by making the third region 1b3 a diffusing surface, it is possible to emit a high-quality white light by exhibiting a diffusing effect and moderating a change in light density near the boundary.

Next, a preferred embodiment of the optical element will be described.

(Example 1)
4A to 4D show an optical element according to Example 1. FIG. The numbers in the figure are dimensions (mm). Each part is given the same reference numeral as in the above-described embodiment. In this example, the leg parts 1j are installed at unequal intervals. 1k is formed.

The refractive surface 1g of the entrance surface 1a and the exit surface 1b are aspherical. Table 1 shows lens data of Example 1.

In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) may be expressed using E (for example, 2.5 × E−3). When the coordinates of the center of the light exit surface of the LED light source are the origin, and the optical axis is a line that passes through the origin and is perpendicular to the exit surface, the optical surface of the optical element is assigned the coefficient shown in Table 1 in the equation (1). It is formed into an aspherical surface that is axisymmetric about the optical axis, which is defined by the above formula.

Here, X (H) is the distance from the origin to the optical axis direction, κ is the conical coefficient, Ai is the aspherical coefficient, A0 is the sag amount at H = 0 of each surface, and H is the optical axis perpendicular to the optical axis. The distance (radius), r is the radius of curvature.

In Example 1, the refracting surface 1g of the incident surface is a single aspherical surface, and the exit surface is composed of a first region 1b1 including the optical axis, a second region 1b2 outside thereof, and a third region 1b3 outside thereof. Consists of regions. However, the third region 1b3 is a mirror surface. The boundary between the first region 1b1 and the second region 1b2 has a step of about 0.005 mm at a position where H = 3 mm, and the boundary between the second region 1b2 and the third region 1b3 is a position where H = 6.2 mm. Has a step of about 0.025 mm (see sag amount SAG (H) in Tables 2 and 3). The step is a step in a direction in which the second region 1b2 is thicker than the other regions 1b1 and 1b3. Further, the surface vertex is on the boundary between the first region 1b1 and the second region 1b2.

Tables 2 and 3 show data such as the sag amount on the exit surface of Example 1. In the table, SAG (H) is a coordinate (unit: mm) in the optical axis direction at the radius H, and the direction in which the light emitted from the LED light source travels is positive. Θ (H) is an angle (unit: degree) formed by the normal of the optical axis at the radius H and the exit surface. When θ (H) continuously changes from positive to negative, it indicates that the angle gradually changes to have a convex lens effect. On the other hand, if it changes discontinuously from positive to negative, it represents a sudden change in convexity. For example, θ (H) changes discontinuously between the first region 1b1 and the second region 1b2 (H = 3 mm), but the light ray angle of the second region 1b2 is smaller than that of the first region 1b1. This means that the light flux is changed toward the light condensing, and a part of the light beams emitted from each other region can be crossed.

SAG (H) ′ is a primary differential value at a radius H, and SAG (H) ″ is a secondary differential value at a radius H. Here, θ (H) and SAG (H) ′ are unit systems. Are different but have the same meaning (angle and differential value), Fig. 5 shows the relationship between radius H and SAG (H), Fig. 6 shows the relationship between radius H and θ (H), 7 shows the relationship between the radius H and SAG (H) ′, and FIG. 8 shows the relationship between the radius H and SAG (H) ″.

From Tables 2 and 3, θ (H) and SAG (H) ′ are discontinuous before and after the boundary between the first region 1b1 and the second region 1b2, and compared with the first region 1b1 before and after this boundary. It can be seen that the refractive surface of the second region 1b2 has a large positive power. That is, the second region 1b2 has a weaker power for diffusing light than the first region 1b1, and thus the light beams emitted before and after the boundary intersect each other. Further, SAG (H) "is a further differentiation of the inclination of the surface, which can be used as an index indirectly representing a change in the light density at the radius H. Thus, the boundary between the first region 1b1 and the second region 1b2 It can be seen that the direction of discontinuity and change is different between the front and the back, as shown in Fig. 1. The light rays on the right side of the figure have a low density and the light rays on the left side have a high density. Is designed to have a lower density, and it can be seen from the relationship between θ (H) and SAG (H) ′ that the density is complemented before and after the boundary.

Here, the illuminance simulation result comparing Example 1 and the comparative example will be described. In the comparative example used here, the third region 1b3 on the exit surface side is expressed by one aspheric function continuous to the optical axis as compared with the first embodiment, that is, the aspheric shape is similar. There are no discontinuous points or steps. Other shapes are the same as those in the first embodiment.

First, consider the ideal model, which is the design goal of optical elements. FIG. 9A is a schematic view of an irradiation surface of an ideal optical element assuming that, for example, a point light source is used, and FIG. 9B is an irradiation surface of the ideal optical element. Is a sectional view in the optical axis direction, and the vertical axis corresponds to illuminance. In the illuminating device, it is ideal to obtain a Gaussian-shaped illuminance curve as shown in FIG. 9B. However, when a surface-emitting light source such as an LED light source is used, the ideal curve is not always obtained. Therefore, a discontinuous portion is provided on the emission surface.

FIG. 9C is a schematic view of the irradiation surface viewed from the top when an optical element having a discontinuity between the first region and the second region of the emission surface is seen, and the dotted line passes through the first region. The illuminance distribution on the irradiation surface by the luminous flux and the solid line passing through the second region are shown. FIG. 9D is a sectional view in the optical axis direction of the irradiated surface. Referring to FIG. 9 (c), it can be seen that there is a portion where the light beams overlap in the vicinity of the connecting portion between the first region and the second region, and the relationship of compensating the illuminance in total. In other words, it can be seen that the illuminance curve approaches the ideal curve shown in FIG. Example 1 was designed based on this idea.

FIG. 10A shows the illuminance curve of Example 1 superimposed on the ideal curve, and FIG. 10B shows the illuminance curve of the comparative example superimposed on the ideal curve. The illuminance curves were drawn independently for the luminous flux emitted from the vicinity of the optical axis of the LED light source (φ0.2 mm) and the luminous flux from the periphery of the LED light source (φ2.3 to 2.5 mm). Here, comparing FIGS. 10A and 10B, with respect to the light beam emitted from the vicinity of the optical axis of the LED light source, in Example 1 and the comparative example, Example 1 has a slightly smaller ideal curve. However, the illuminance curve is almost the same. The reason why the illuminance near the optical axis is reduced with respect to the ideal curve is that the light beam reflected inside the optical element is reflected / scattered on the back surface or the light beam that is transmitted from the back surface and diffusely reflected on the substrate. This is because they gather near the center of the surface to be irradiated and eventually have an illuminance distribution close to the ideal curve.

On the other hand, the luminous flux emitted from the periphery of the LED light source is clearly different between Example 1 and the comparative example. FIG. 11 is a graph in which the illuminance curve relating to the luminous flux emitted from the entire emission surface of the LED light source in Example 1 and the comparative example is superimposed on the ideal curve. Referring to FIG. 11, the illuminance curve of Example 1 is closer to the ideal curve than the comparative example near the optical axis, and the effect of Example 1 was confirmed. In FIG. 11, the illuminance curve of Example 1 has a strong wave at a position away from the optical axis. However, since the original illuminance is small at such a peripheral position, the influence is small in actual use.

Next, effects in the case where the third region of the emission surface is a diffusion surface in Example 1 will be described. FIG. 12A is an enlarged view showing an optical path in the vicinity of the step ST at the boundary between the second region 1b2 and the third region 1b3 in the example in which the third region 1b3 on the emission surface is a mirror surface. b) is an enlarged view showing an optical path when light beams emitted from the second region 1b2 and the third region 1b3 are incident on a diffusion plate as an irradiated surface. On the other hand, FIG. 12C is an enlarged view showing an optical path in the vicinity of the step ST ′ at the boundary between the second region 1b2 and the third region 1b3 ′ in the example in which the third region 1b3 ′ on the emission surface is the diffusion surface. FIG. 12D is an enlarged view showing an optical path when the light beams emitted from the second region 1b2 and the third region 1b3 ′ are incident on the lower surface of the diffusion plate PT as the irradiated surface. The step ST ′ is also a diffusion surface.

If the third region 1b3 is a mirror surface, as shown in FIG. 12A, the light emitted from the second region 1b2 and the light emitted from the third region 1b3 do not intersect due to the vignetting effect of the step ST. Therefore, as shown in FIG. 12B, when entering the lower surface of the diffusion plate PT, a shadow portion SH having a low light amount is generated. Due to the vignetting effect, the light beam emitted in different directions after passing through the step ST is a light beam having a strong bluish or yellowish tint and is likely to cause color unevenness. Therefore, the step ST is preferably not too large.

On the other hand, as shown in FIG. 12C, the light emitted from the third region 1b3 is diffused to partially change the emission direction, so that the diffusion is performed as shown in FIG. When entering the lower surface of the plate PT, a shadow portion caused by the vignetting effect becomes inconspicuous. By setting the step ST ′ as a diffusing surface, the emitted light is diffused after passing through the step ST ′, so that the occurrence of color unevenness can be suppressed.

FIG. 13 is a graph in which an illuminance curve relating to a light beam emitted from the entire surface of the LED light source in Example 1 in which the third region is a mirror surface and a diffusion surface is superimposed on the ideal curve. It can be seen that if the third region is a diffusing surface, the unevenness of the curve is reduced compared to the case where the third region is a mirror surface, particularly in the range PR away from the optical axis, and closer to the ideal curve.

(Example 2)
FIG. 14 shows an optical element according to Example 2. The numbers in the figure are dimensions (mm). In this embodiment, on the outer peripheral surface 1f, recesses 1m serving as assembling references are formed in the vicinity of three leg portions 1j arranged at equal intervals in the circumferential direction. The incident surface shape and the output surface shape are the same as those in the first embodiment.

The present invention is not limited to the embodiments and examples described in the specification, and includes other examples and modifications based on the embodiments, examples, and technical ideas described in the present specification. It will be apparent to those skilled in the art.

DESCRIPTION OF SYMBOLS 1 Scientific element 1a Incident surface 1b Output surface 1b1 1st area | region 1b2 2nd area | region 1b3 3rd area | region 1d Bottom face 1f Outer peripheral surface 1g Refraction surface 1h Diffusion surface 1i Step difference 1j Leg part 1k Convex part 1m Concave part B1, B2 Boundary ST step 2LED Light source 2a Light emission surface 3 Circuit board

Claims

An optical element for a backlight including an incident surface on which a light beam from an LED light source is incident and an output surface that emits the light beam,
The LED light source is a combination of an LED chip and a phosphor having a larger area than the LED chip in the optical axis direction.
The exit surface of the optical element has a boundary that is divided into two regions in the direction perpendicular to the optical axis, a region closer to the optical axis than the boundary is defined as a first region, and a region outside the boundary is defined as a second region. The function defining the exit surface shape of the first region and the function defining the exit surface shape of the second region are discontinuous,
Of the light beams emitted from the LED light source and entering the optical element via the incident surface, at least a light beam emitted from the first region and a light beam emitted from the second region across the boundary are at least An optical element that partially intersects.
The LED light source emits the LED chip that emits a light beam of a first color and the phosphor that emits a second color different from the first color when the light beam of the first color enters. The optical element according to claim 1, wherein:
3. The optical element according to claim 1, wherein a step is formed at the boundary by shifting the second region away from the LED light source with respect to the first region.
4. The optical element according to claim 1, wherein the step is 5 μm or more.
The normal line of the first region at a position adjacent to the boundary is different from the normal line of the second region at a position adjacent to the boundary. Optical elements.
6. The exit surface according to claim 1, wherein the exit surface has a recess, and the boundary is formed at a position within ± 10% of the exit surface diameter with respect to a surface vertex of the exit surface. An optical element according to 1.
A third region is formed on the exit surface on the outer side in the direction perpendicular to the optical axis of the second region, and a function defining the exit surface shape of the second region, and the exit surface shape of the third region The optical element according to any one of claims 1 to 6, wherein the function defining the distance is discontinuous.
The optical element according to claim 7, wherein a step is formed by shifting the third region toward the side closer to the LED light source with respect to the second region at the other boundary.
9. The optical element according to claim 7, wherein a diffusion surface is formed in the third region.
10. The optical element according to claim 1, wherein the exit surface has an aspherical shape, and the vicinity of the optical axis of the first region is recessed.
11. The optical element according to claim 1, wherein the incident surface has a concave aspherical shape.
An LED comprising a combination of an LED chip that emits a first color light beam and a phosphor that emits light in a second color different from the first color by the first color light beam emitted from the LED chip. An illumination device comprising: a light source; and the optical element according to any one of claims 1 to 11.