JP2014002951A - Lighting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting apparatus that suitably lights up a panel from behind, suppresses color unevenness of white light although being relatively thin, and further attains higher light taking-in efficiency and a wider light distribution angle, and is equipped with an optical element which can be manufactured at low cost.SOLUTION: An LED light source 2 is a white LED whose light emission surface 2a is plane and the light emission surface 2a has an external diameter of 2.3 mm or more and 3.0 mm or less. An optical element 1 has an incidence plane 1a on which luminous flux from the LED light source 2 is made incident and an emission plane 1b opposed to the incidence surface 1a and emitting the luminous flux, The incidence plane 1a has an effective diameter of 3.2 mm or more and 4.0 mm or less and an optical axial depth of 1.0 φmm or more and 1.5 φmm or less, and the emission plane 1b has an effective diameter of 10 or more and 20 mm or less, and includes a recessed part in the center and a projection part at its periphery, and an inflection point of the emission plane 1b is at a position which is 33% or more and 40% or less of an effective radius of the mission surface 1b from the center of the optical axis in a direction orthogonal to the optical axis. The optical element 1 has an on-axis thickness of 0.5 mm or more and 1.0 mm or less.

Description

  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 illumination so that light passes through the surface member.

  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.

  As described above, when an LED light source is used as a backlight of a liquid crystal display device, the LED light source chip itself is small and the light distribution is narrow. Therefore, if such a chip is arranged directly on the back side of the liquid crystal panel, uniform illuminance is ensured. For this purpose, countless chips are required, which is not realistic. Therefore, an optical element that converts light emitted from the LED chip into illumination light with uniform illuminance is required. Patent Documents 1 and 2 disclose an optical element for a backlight for liquid crystal that can convert light from an LED light source into illumination light with as uniform illuminance as possible.

JP 2010-211246 JP 2009-43628

  By the way, since a general liquid crystal display device has an advantage of being thin for a large screen, the backlight is also required to be thin (low profile). For this reason, it is preferable to reduce the thickness of the optical element in the optical axis direction as much as possible. Therefore, Patent Documents 1 and 2 disclose a thin optical element.

  On the other hand, an LED light source that emits white light is used to develop an image displayed on the liquid crystal panel with a natural color. As the LED light source that emits white light in this manner, at present, a combination of a blue LED chip that emits blue light and a phosphor that emits yellow light by blue light emitted from the blue LED chip is widely used. It has been.

  However, as a characteristic of a white LED light source using a blue LED chip and a phosphor, color unevenness called a yellow ring centering on the optical axis may occur in white light that has passed through the phosphor. 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. However, even when white light from such an LED light source is incident on an optical element having a relatively large thickness in the optical axis direction, a certain amount of color mixing occurs due to the diffusion effect, and color unevenness is conspicuous. However, in particular, in a thin optical element, since the optical path length in the optical element is short, such a diffusion effect cannot be originally expected. However, neither of Patent Documents 1 and 2 is intended to widen the light distribution angle and reduce luminance unevenness, and does not mention at all how to eliminate color unevenness in white light.

  In addition, an illuminating device used as a backlight requires an optical element that can increase the light capturing efficiency, realize a wide light distribution angle, and can be manufactured at low cost. However, cited documents 1 and 2 do not mention such an optical element.

  The present invention has been made in view of the problems of the prior art, and is suitable for illuminating from behind the panel. It is possible to suppress color unevenness of white light while being relatively thin. It is an object of the present invention to provide an illuminating device provided with an optical element that can improve the capture efficiency, realize a wide light distribution angle, and can be manufactured at low cost.

The lighting device according to claim 1 is a lighting device having a light source and an optical element,
The light source is a white LED having a flat emission surface,
The outer diameter φ of the light emitting surface of the light source is 2.3 mm or more and 3.0 mm or less,
The optical element is made of plastic,
The optical element has an incident surface on which a light beam from the light source is incident, and an exit surface that faces the incident surface and emits the light beam from the optical element,
The effective diameter of the incident surface is 3.2 mm or more and 4.0 mm or less,
The depth in the optical axis direction of the incident surface is 1.0φmm or more and 1.5φmm or less,
The effective diameter of the emission surface is 10 mm or more and 20 mm or less,
The emission surface has a concave portion at the center and a convex portion at the periphery thereof.
The inflection point of the exit surface is in the direction orthogonal to the optical axis from the center of the optical axis, at a position of 33% or more and 40% or less of the effective radius of the exit surface,
The on-axis thickness of the optical element is 0.5 mm or more and 1.0 mm or less.

  Many of white LEDs that are currently available as the light source have an outer diameter φ of 2.3 mm or more and 3.0 mm or less on the light emitting surface. In the case where such a white LED is used, if the effective diameter of the incident surface of the optical element is set to 3.2 mm or more and 4.0 mm or less, the occurrence of color unevenness can be prevented, and the efficiency of capturing light from the light source can be improved. The optical element can be increased in size and the loss of light quantity can be prevented, and the diameter of the optical element can be prevented from increasing. This point will be described in detail.

  First, from the viewpoint of increasing the efficiency of capturing light from the light source, the size of the incident surface of the optical element is larger than the outer diameter of the light emitting surface in order to capture the light from the light source into the optical element. There is a need to. However, if the size of the incident surface is made too large, the exit surface has to be enlarged accordingly, and the optical element becomes larger in diameter. Therefore, it is considered preferable to make the size of the incident surface slightly larger than the outer diameter of the light emitting surface, and when such a design is performed, color unevenness will occur this time. Noticed. From such knowledge, the present inventor can secure a large capture efficiency by sufficiently capturing the light of the light source, yet does not cause color unevenness, and suppresses an increase in the diameter of the optical element. It has been found that it is effective to define the size of the effective diameter of the incident surface as described above.

  On the other hand, in order to use the lighting device as a backlight, the problem of widening the light distribution angle must be cleared, but in order to obtain an optical element having a large light distribution angle without causing color unevenness, It is necessary to keep the molding accuracy near the optical axis where the amount of transmitted light is the highest. However, if the on-axis thickness of the optical element is too thin, the resin is not properly filled during resin molding, and the transfer accuracy of the mold is lowered, and the molding accuracy near the important optical axis is reduced. In addition, there is a risk of causing color unevenness and narrowing of the light distribution angle. On the other hand, if the axial thickness of the optical element is increased, the resin is easily filled into the mold, but if the resin is not sufficiently cooled, sinking or warping is likely to occur, while the resin is sufficiently cooled. In order to do so, the cycle time becomes longer, and the molding efficiency is lowered.

  Therefore, the present inventor can reduce the cycle time while improving the molding accuracy to such an extent that the problem of uneven color and the problem of light distribution angle are not caused, and the on-axis thickness of the optical element as a shape suitable for mass production. Has been found to be preferably 0.5 mm or more and 1.0 mm or less.

  In order to increase the light distribution angle, it is preferable that both the entrance surface and the exit surface of the optical element have power. From this viewpoint, the entrance surface is preferably deepened to some extent, for example, the optical axis of the entrance surface. The depth of the direction is preferably 1.0 mm or more and 1.5 mm or less when the outer diameter of the light emitting surface of the light source is φ mm. Furthermore, in order to obtain a preferable light distribution, it is desirable that the inflection point of the exit surface is in the direction perpendicular to the optical axis from the center of the optical axis and at a position of 33% or more and 40% or less of the effective radius of the exit surface. Also, the present inventor has found out.

  The lighting device according to the present invention includes a light source and an optical element. The light source is a white LED (Light Emitting Diode) having a flat emission surface.

  As the white LED, a combination of a blue LED chip and a phosphor such as a YAG phosphor that emits yellow light by blue light emitted from the blue LED chip is preferably used. As white LED, what was described, for example in Unexamined-Japanese-Patent No. 2008-231218 can be used, However, It is not restricted to this.

  Specifically, the white LED includes an LED chip and a phosphor layer formed on the LED chip so as to cover the LED chip. The LED chip emits light of a first predetermined wavelength (light of the first color), 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.

  In addition, as such an LED chip, a well-known blue LED chip can be used. 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.

  The phosphor layer includes a phosphor that converts light having a first predetermined wavelength emitted from the LED chip into light having a second predetermined wavelength (light of a second color). In an embodiment described later, blue light emitted from the LED chip is converted into yellow light.

  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 outer diameter φ of the light emitting surface of the light source is 2.3 mm or more and 3.0 mm or less. Here, the outer diameter of the light emitting surface means the diameter of the inscribed circle when the light emitting surface is a polygon.

  The optical element is disposed on the light emission side of the light source, and has a concave incident surface on which light emitted from the light source is incident and a generally convex emission surface that emits light emitted from the light source to the outside. preferable. Further, it is preferable that the concave incident surface of the optical element has an aspherical refracting surface through which a normal line at the center of the light emitting surface passes. The entrance surface of the lens and the light emission surface of the light source are preferably not in contact with each other, and the space between the entrance surface and the light source is preferably filled with air. The effective diameter of the incident surface is preferably 3.2 mm or more and 4.0 mm or less. In addition, the depth of the incident surface in the optical axis direction is desirably 1.0 mm or more and 1.5 mm or less.

  The bottom surface of the optical element is preferably a diffusing surface. The diffusion surface can be obtained, for example, by subjecting a part of the transfer surface of the mold to roughing processing such as shot peening or embossing to roughen the surface roughness and then transfer molding a resin or the like.

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

  The effective diameter of the exit surface of the optical element is 10 mm or more and 20 mm or less. The exit surface preferably has a concave portion at the center and a convex portion at the periphery thereof. The inflection point of the exit surface is in the direction orthogonal to the optical axis from the center of the optical axis, 33% or more of the effective radius of the exit surface, 40 % Or less is preferable. The amount of sag at the effective diameter position on the exit surface is preferably 2.61 mm or more. Moreover, it is preferable that the incident surface also has an inflection point. The axial thickness of the optical element is 0.5 mm or more and 1.0 mm or less.

  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.

  According to the present invention, it is suitable for illuminating from behind the panel, and can suppress uneven color of white light while being relatively thin, further increase the light capture efficiency, and realize a wider light distribution angle. In addition, it is possible to provide an illumination device including an optical element that can be manufactured at low cost.

It is the figure which looked at the LED illuminating device concerning this Embodiment from the output surface side. It is the figure which cut | disconnected the structure of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is the figure which looked at the LED lighting apparatus concerning this Embodiment from the entrance plane side. 4A is a diagram showing the effective radius on the horizontal axis and the sag amount (displacement amount in the optical axis direction from the surface apex) on the vertical axis, and FIG. 4B is the horizontal axis. It is a figure which takes the 1st-order differential value of the effective radius and the sag amount of the incident surface on the vertical axis. FIG. 5A is a diagram showing the effective radius on the horizontal axis and the sag amount (displacement amount in the optical axis direction from the surface apex) on the vertical axis, and FIG. 5B is the horizontal axis. It is a figure which takes the effective radius and the vertical axis | shaft taking the 1st-order differential value of the sag amount of an output surface.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a view of the illumination device according to the present embodiment as viewed from the exit surface side. FIG. 2 is a view of the configuration of FIG. 1 taken along the line II-II and viewed in the direction of the arrow. FIG. 3 is a view of the illumination device according to the present embodiment as viewed from the incident surface side. The numbers in the figure are dimensions (mm).

  The lighting 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, the LED light source 2 is formed by laminating an LED chip that emits blue light and a yellow phosphor provided on the light emission side, and has a square plate shape as a whole, and emits light. The surface (outgoing surface) 2a is flat.

  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 emits light incident from the concave incident surface 1a on which light emitted from the LED light source 2 is incident, and the incident surface 1a. And a bottom surface 1d facing the substrate 3, and an outer peripheral surface 1f which is a cylindrical surface or a conical surface provided on the outer periphery of the output surface 1b. The outer peripheral surface 1f is a part where a gate is provided when the optical element 1 is injection-molded.

  The concave incident surface 1a is an aspherical refracting surface through which the normal line at the center of the light emitting surface 2a of the LED light source 2 passes.

  Similarly to the diffusion surface 1h, the bottom surface 1d can be a rough surface having a diffusion action by increasing the roughness of the corresponding transfer surface of the mold. 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, as shown in FIG. 3, the bottom surface 1d has three leg portions 1j at equal intervals in the circumferential direction, and the leg portions 1j are in direct contact with the surface of the substrate 3, or It is indirectly attached via a pedestal (not shown in FIG. 2). 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 1j can be a roughened surface having a diffusing action by increasing the roughness of the corresponding transfer surface of the mold, like the diffusing surface 1h.

  When the optical element 1 is attached to the LED light source 2, a gap is formed in the optical axis direction between the bottom surface 1 d and the light emission surface 2 a of the LED light source 2. Thereby, the light emitted from the light emitting surface 2a can be turned to the bottom surface 1d side.

  The outer diameter of the optical element 1 is 10 to 20 mm, the outer diameter φ of the light emitting surface 2a of the LED light source 2 is 2.3 to 3.0 mm, and the effective diameter of the incident surface 1a of the optical element 1 is 3.2. The depth in the optical axis direction of the incident surface 1a is 1.0φ to 1.5φ mm, and the axial thickness of the optical element 1 is 0.5 to 1.0 mm. The exit surface 1b has a concave portion at the center and a convex portion at the periphery thereof, and the inflection point of the exit surface 1b is in the direction orthogonal to the optical axis from the center of the optical axis, 33% or more and 40% or less of the effective radius of the exit surface. In the position.

  In the present embodiment, mixed light in the vicinity of the center of the light emitted from the light emitting surface 2a of the LED light source 2 is incident from the incident surface 1a, while the peripheral light is incident from the bottom surface 1d. The light incident on the optical element 1 is emitted from the emission surface 1b with a peak of the light distribution angle at a position of 75 to 85 degrees. Here, by allowing ambient light, which often contains a yellow component, to enter through the bottom surface 1d having a diffusing action, a diffusion effect occurs, and the yellow component bias disappears. Thereby, high-quality white light can be emitted.

  Next, a preferred embodiment of the optical element will be described. This embodiment has the shape shown in FIGS. The entrance surface (referred to as S1) and the exit surface (referred to as S2) are aspherical. The aspherical shape is expressed by the following “Equation 1” where the vertex of the surface is the origin, the X axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数

However,
Ai: i-order aspheric coefficient R: radius of curvature K: conic constant

Table 1 shows the aspheric shape factor. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).

  In this embodiment, the outer diameter φ of the light emitting surface of the light source is 2.5 mm, the outer diameter of the optical element is 15.40 mm, the effective diameter of the incident surface is 3.79 mm, and the depth in the optical axis direction from the bottom surface of the incident surface. Is 2.95 (1.18φ) mm, the on-axis thickness is 0.81 mm, and the light distribution angle is 77 °.

  4A is a diagram showing the effective radius on the horizontal axis and the sag amount (displacement amount in the optical axis direction from the surface apex) on the vertical axis, and FIG. 4B is the horizontal axis. It is a figure which takes the 1st-order differential value of the effective radius and the sag amount of the incident surface on the vertical axis. FIG. 5A is a diagram showing the effective radius on the horizontal axis and the sag amount (displacement amount in the optical axis direction from the surface apex) on the vertical axis, and FIG. 5B is the horizontal axis. It is a figure which takes the effective radius and the vertical axis | shaft taking the 1st-order differential value of the sag amount of an output surface. The position at which the sign of the first-order differential value of the sag is reversed becomes the inflection point. The inflection point of the exit surface is 2.75 mm (36% of the effective radius of the exit surface).

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. For example, the present invention can be used not only for illumination of a liquid crystal panel but also as an illumination device for signboard illumination.

DESCRIPTION OF SYMBOLS 1 Optical element 1a Incident surface 1b Output surface 1d Bottom surface 1f Outer peripheral surface 1j Leg part 2 LED light source 2a Light emission surface 3 Circuit board

Claims (1)

An illumination device having a light source and an optical element,
The light source is a white LED having a flat emission surface,
The outer diameter φ of the light emitting surface of the light source is 2.3 mm or more and 3.0 mm or less,
The optical element is made of plastic,
The optical element has an incident surface on which a light beam from the light source is incident, and an exit surface that faces the incident surface and emits the light beam from the optical element,
The effective diameter of the incident surface is 3.2 mm or more and 4.0 mm or less,
The depth in the optical axis direction of the incident surface is 1.0φmm or more and 1.5φmm or less,
The effective diameter of the emission surface is 10 mm or more and 20 mm or less,
The emission surface has a concave portion at the center and a convex portion at the periphery thereof.
The inflection point of the exit surface is in the direction orthogonal to the optical axis from the center of the optical axis, at a position of 33% or more and 40% or less of the effective radius of the exit surface,
An on-axis thickness of the optical element is not less than 0.5 mm and not more than 1.0 mm.

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