Lighting device

Abstract

This lighting device comprises a housing, a light source, an aspheric lens, a wavelength conversion member, and a wavelength separation filter. The housing has a first opening that is open to a lighting space. The light source emits excitation light into the housing. The aspheric lens is positioned inside the housing and flattens the light intensity distribution of the excitation light received from the light source. The wavelength conversion member is positioned inside the housing and emits, on the basis of the excitation light, fluorescence having a spectrum different from that of the excitation light as illuminating light. The wavelength separation filter is positioned inside the housing, guides the excitation light from the aspheric lens to the wavelength conversion member, and guides the fluorescence from the wavelength conversion member to the first opening.

Description

lighting equipment CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2022-168283 (filed October 20, 2022), the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to a lighting device.

[0003] Conventionally, devices have been proposed that include a light source, a wavelength conversion element, and an optical component that reflects light from the light source onto the wavelength conversion element and transmits light from the wavelength conversion element (for example, Patent Document 1).

[0004] JP 2022-38680 A

[0005] A lighting device is disclosed.

[0006] In one embodiment, the lighting device emits illumination light into an external illumination space. The lighting device includes a housing, a light source, an aspherical lens, a wavelength conversion member, and a wavelength separation filter. The housing has a first opening that opens into the illumination space. The light source emits excitation light into the interior of the housing. The aspherical lens is located inside the housing. The excitation light from the light source is incident on the aspherical lens. The aspherical lens flattens the intensity distribution of the excitation light. The wavelength conversion member is located inside the housing. The excitation light from the aspherical lens is incident on the wavelength conversion member. The wavelength conversion member emits fluorescence as illumination light having a spectrum different from that of the excitation light based on the excitation light. The wavelength separation filter is located inside the housing and guides the excitation light from the aspherical lens to the wavelength conversion member and guides the fluorescence from the wavelength conversion member to the first opening.

[0007] FIG. 1 is a diagram schematically illustrating an example of an optical system of an illumination device according to a first embodiment; FIG. 1 is a diagram schematically illustrating an example of a configuration of an optical system viewed along a fast axis; FIG. 1 is a diagram schematically illustrating an example of a configuration of an optical system viewed along a slow axis; FIG. 2 is a graph for explaining the shape of an aspherical surface of an aspherical lens; FIG. 3 is a graph for explaining the shape of an aspherical surface; FIG. 4 is a diagram schematically illustrating an example of an intensity distribution of excitation light; FIG. 5 is a graph for explaining the shapes of aspherical surfaces respectively corresponding to a plurality of Conic coefficients; FIG. 2 is a diagram schematically illustrating an example of a configuration of an illumination device according to a second embodiment; FIG. 3 is a graph for explaining the shape of an aspherical surface of an aspherical lens; FIG. 4 is a graph for explaining the shape of an aspherical surface; FIG. 5 is a diagram for explaining another example of an aspherical surface of an aspherical lens; FIG. 6 is a diagram schematically illustrating an example of a configuration of an illumination device according to a third embodiment;

[0008] The inventor has created a technology for reducing unevenness in illumination light in an illumination device. First to fourth embodiments of this technology will be described below with reference to the drawings.

[0009] <1. First Embodiment> <1-1. Schematic Configuration of Illumination Device 1> FIG. 1 is a diagram schematically illustrating an example of the configuration of an illumination device 1 according to a first embodiment. As shown in FIG. 1, the illumination device 1 is a device that emits fluorescence L1 as illumination light into an external illumination space S1. The illumination space S1 is, for example, a space where a person may stay or pass through. More specifically, the illumination space S1 may be an interior space of a specific building or a corridor connecting rooms. The illumination device 1 is disposed, for example, on the ceiling of the illumination space S1. The fluorescence L1 emitted from the illumination device 1 can directly illuminate an object within the illumination space S1. Here, "directly" refers to the fluorescence L1 being irradiated onto the object without passing through optical components such as a lens or a spatial light modulator. A person within the illumination space S1 can visually recognize the shape and color of the object illuminated by the fluorescence L1. Illuminating an object with more uniform fluorescence L1 with less unevenness allows a person to more appropriately visually recognize the shape and color of the object.

[0010] 1, the lighting device 1 includes a light source 2, an optical system 3, a wavelength conversion member 4, a wavelength separation filter 5, an optical system 6, and a housing 7. Below, an example of each component will first be outlined, and then described in detail.

[0011] The housing 7 houses the light source 2, the optical system 3, the wavelength conversion member 4, the wavelength separation filter 5, and the optical system 6. In the example of Fig. 1, the housing 7 includes a housing section 71 and a housing section 72. The housing section 71 houses the wavelength conversion member 4, the wavelength separation filter 5, and the optical system 6, and the housing section 72 houses the light source 2 and the optical system 3.

[0012] The housing 7 has an exit opening (corresponding to a first opening) 7a. In the example of FIG. 1 , the exit opening 7a is formed at an end of the housing portion 71. Fluorescence L1 as illumination light is emitted from the exit opening 7a to the illumination space S1. The exit opening 7a is a space connecting the internal space of the housing 7 and the illumination space S1. The exit opening 7a functions as an outlet for the fluorescence L1 from the internal space of the housing 7 to the illumination space S1. As exemplified in FIG. 1 , a lens does not have to be located inside the exit opening 7a. Furthermore, optical components such as a lens and a spatial light modulation unit do not have to be located forward of the exit opening 7a in the emission direction.

[0013] In the example of FIG. 1 , the wavelength conversion member 4, the wavelength separation filter 5, the optical system 6, and the emission opening 7a are aligned along the first direction. Therefore, the housing 71 has an elongated shape that is long in the first direction. When the lighting device 1 is installed on a ceiling, the lighting device 1 is installed on the ceiling with the first direction aligned vertically. In the example of FIG. 1 , the light source 2, the optical system 3, and the wavelength separation filter 5 are aligned along a second direction that intersects with the first direction. In the example of FIG. 1 , the housing 72 is attached to the side of the housing 71, and the internal spaces of the housing 72 and the housing 71 are connected to each other through an opening 74 formed in the side of the housing 71.

[0014] The light source 2 emits excitation light L0 into the housing 7. As shown in FIG. 1 , the light source 2 has an emission portion (e.g., an emission surface) 201 that emits the excitation light L0. The excitation light L0 may be, for example, light having a peak in a wavelength range of 415 nm or less, more specifically, in a wavelength range of 380 nm or more and 415 nm or less. As a more specific example, the excitation light L0 may be purple light having a peak near 405 nm. Note that the excitation light L0 is not necessarily limited to purple light, and may be, for example, blue light having a peak near 450 nm.

[0015] The intensity distribution of the excitation light L0 immediately after the light source 2 has, for example, a mountain-like shape. The intensity distribution here refers to the intensity distribution in a cross section perpendicular to the direction of light propagation. In other words, the intensity distribution of the excitation light L0 immediately after the light source 2 is the intensity distribution of the excitation light L0 in a cross section perpendicular to the optical axis AX0 of the light source 2. This intensity distribution of the excitation light L0 has, for example, a mountain-like shape in which the intensity in the central portion is higher than the intensity in the peripheral portion. As a more specific example, the intensity distribution has a single mountain-like shape with a single peak intensity. In the example of FIG. 1, the intensity distribution of the excitation light L0 in a cross section immediately after the emission portion 201 of the light source 2 is schematically shown directly below the light source 2.

[0016] As will be described later, the excitation light L0 from the light source 2 passes through the optical system 3, the wavelength separation filter 5, and the lenses 61B and 61A of the optical system 6, and is incident on the wavelength conversion member 4.

[0017] The optical system 3 can adjust the intensity distribution of the excitation light L0. Specifically, the optical system 3 flattens the intensity distribution of the excitation light L0. The optical system 3 includes an aspherical lens 31. The aspherical lens 31 can adjust the intensity distribution of the excitation light L0 by refracting each ray of the excitation light L0. As will be described in detail later, the aspherical lens 31 refracts each ray of the excitation light L0 so that the intensity distribution of the excitation light L0 on the wavelength conversion member 4 is flattened. In the example of FIG. 1, the intensity distribution of the excitation light L0 on the wavelength conversion member 4 is schematically shown to the right of the wavelength conversion member 4. In the example of FIG. 1, the intensity distribution of the excitation light L0 on the wavelength conversion member 4 has a so-called top hat shape.

[0018] 1, the optical system 3 may further include a cylindrical lens 32. The cylindrical lens 32 can adjust the aspect ratio of the intensity distribution of the excitation light L0. The cylindrical lens 32 will also be described in detail later.

[0019] The excitation light L0 from the optical system 3 passes through the opening 74 and enters the wavelength separation filter 5. The wavelength separation filter 5 guides the excitation light L0 to the wavelength conversion member 4. In the example of Fig. 1, the wavelength separation filter 5 reflects the excitation light L0 toward the wavelength conversion member 4, and guides the excitation light L0 to the wavelength conversion member 4. In the example of Fig. 1, the excitation light L0 from the wavelength separation filter 5 enters the wavelength conversion member 4 via lenses 61B and 61A.

[0020] The wavelength conversion member 4 contains a phosphor. The wavelength conversion member 4 emits fluorescence L1 based on the incident excitation light L0. The fluorescence L1 has a spectrum different from that of the excitation light L0. Specifically, the peak wavelength of the fluorescence L1 is longer than that of the excitation light L0, and the fluorescence L1 is visible light. The fluorescence L1 travels from the wavelength conversion member 4 toward the wavelength separation filter 5, and in the example of FIG. 1, it enters the wavelength separation filter 5 via lenses 61A and 61B. The wavelength separation filter 5 guides the fluorescence L1 to the exit opening 7a. In the example of FIG. 1, the wavelength conversion member 4, the wavelength separation filter 5, and the exit opening 7a are arranged in this order along the first direction, so the wavelength separation filter 5 transmits the fluorescence L1 from the wavelength conversion member 4 toward the exit opening 7a.

[0021] The optical system 6 includes one or more lenses 61 located on the path of the fluorescence L1 between the wavelength conversion member 4 and the exit opening 7a. In the example of FIG. 1, lenses 61A, 61B, and 61C are shown as the lenses 61. Lenses 61A to 61C are lined up between the wavelength conversion member 4 and the exit opening 7a. In the example of FIG. 1, lenses 61A and 61B are located between the wavelength conversion member 4 and the wavelength separation filter 5. Lens 61A is located closer to the wavelength conversion member 4 than lens 61B. Lens 61C is located between the wavelength separation filter 5 and the exit opening 7a. Therefore, in the example of FIG. 1, the wavelength conversion member 4, lens 61A, lens 61B, wavelength separation filter 5, lens 61C, and exit opening 7a are arranged in this order along the first direction.

[0022] The optical system 6 focuses the fluorescence L1 on a virtual image plane IS1 on the side of the exit opening 7a, while emitting the fluorescence L1 from the exit opening 7a at a predetermined light distribution angle φ2. The light distribution angle φ2 here is, for example, the spread angle of a portion of the fluorescence L1 that has half the peak intensity. The light distribution angle φ2 can also be called the half-value angle. In short, the optical system 6 collects the fluorescence L1 on the side of the exit opening 7a, while emitting the fluorescence L1 from the exit opening 7a at the predetermined light distribution angle φ2.

[0023] The optical system 6 forms an image of the fluorescence L1 in the wavelength conversion member 4 on a virtual image plane IS1, and therefore the optical system 6 can also be said to be a so-called imaging optical system. The virtual image plane IS1 may be a flat surface or a curved surface. When the image plane IS1 is a curved surface, an inexpensive lens can be used as the lens 61 of the optical system 6.

[0024] As described above, the illumination device 1 can emit the fluorescence L1 into the illumination space S1. Moreover, the illumination device 1 includes the aspherical lens 31. The aspherical lens 31 refracts each ray of the excitation light L0 so as to flatten the intensity distribution of the excitation light L0 on the wavelength conversion member 4. Therefore, the excitation light L0 is more uniformly incident on the wavelength conversion member 4.

[0025] For comparison, a comparative structure will be described in which excitation light L0 having a mountain-shaped intensity distribution is incident on the wavelength conversion member 4. The wavelength conversion member 4 emits fluorescence L1 at an intensity corresponding to the intensity of the excitation light L0, so that the fluorescence L1 is emitted at a higher intensity in the center and at a lower intensity in the peripheral portion. This results in greater variation (unevenness) in the intensity distribution of the fluorescence L1 emitted from the lighting device 1.

[0026] In contrast to this, in the present embodiment, the aspherical lens 31 causes the excitation light L0 having a more uniform intensity distribution to be incident on the wavelength conversion member 4. For example, the excitation light L0 having a top-hat shaped intensity distribution is incident on the wavelength conversion member 4. This allows the wavelength conversion member 4 to emit the fluorescence L1 more uniformly. Therefore, the lighting device 1 can emit the fluorescence L1 into the illumination space S1 with less unevenness, and can realize a high-quality illumination space S1 with less glare.

[0027] Furthermore, if the total light amount is the same as that of the excitation light L0 having a top-hat intensity distribution, the peak intensity of the excitation light L0 having a mountain-shaped intensity distribution is relatively high. Therefore, the fluorescence L1 emitted from the central portion of the wavelength conversion member 4 may become saturated. In this case, the intensity of the excitation light L0 cannot be fully utilized in the central portion. In contrast, in this embodiment, excitation light L0 having a lower peak intensity and a more uniform intensity distribution is incident on the wavelength conversion member 4, thereby reducing saturation of the fluorescence L1. Therefore, the lighting device 1 can emit the fluorescence L1 into the illumination space S1 with higher efficiency.

[0028] Furthermore, since the peak intensity of the excitation light L0 having a mountain-shaped intensity distribution is high, the temperature in the central part of the wavelength conversion member 4 becomes high, which is likely to lead to thermal deterioration of the wavelength conversion member 4. In contrast, in the present embodiment, the excitation light L0 having a low peak intensity and a more uniform intensity distribution is incident on the wavelength conversion member 4, so the degree of thermal deterioration of the wavelength conversion member 4 can be reduced.

[0029] Furthermore, because the aspherical lens 31 flattens the intensity distribution of the excitation light L0, more of the excitation light L0 can be incident on the wavelength conversion member 4. For example, if frosted glass or an array lens were used instead of the aspherical lens 31, the intensity distribution of the excitation light L0 would be flattened, but the excitation light L0 would be scattered at the surface of the frosted glass or at the boundaries between the lenses of the array lens, reducing the amount of excitation light L0 incident on the wavelength conversion member 4. In contrast, the aspherical lens 31 can transmit more of the excitation light L0, thereby increasing the amount of excitation light L0 incident on the wavelength conversion member 4. In other words, the illumination device 1 can more efficiently emit the fluorescence L1 into the illumination space S1.

[0030] Furthermore, since the thickness of the aspherical lens 31 is not so large, the size of the lighting device 1 can be reduced compared to when a light guide member such as a rod lens is used.

[0031] It should be noted that the above description does not intend to prohibit the lighting device 1 of this embodiment from including optical components such as frosted glass, an array lens, and a rod lens in addition to the aspherical lens 31.

[0032] An example of each component of the lighting device 1 will be described in detail below.

[0033] <1-2. Light Source 2> The light source 2 may include, for example, a semiconductor laser element such as a laser diode (LD), a vertical cavity surface emitting laser (VCSEL), a light emitting diode (LED), or a super luminescent diode (SLD). The light source 2 may include a single light emitting element. The emission section 201 of the light source 2 may be the emission end of a light emitting element. For example, a gallium nitride (GaN) semiconductor laser that emits 405 nm violet laser light as excitation light L0 may be used as the light emitting element.

[0034] The light source 2 can emit excitation light L0 having a mountain-shaped intensity distribution. Here, the divergence angle of the excitation light L0 emitted by the light source 2 on a first axis perpendicular to the optical axis AX0 is larger than the divergence angle on a second axis perpendicular to the optical axis AX0 and the first axis (see also FIG. 2 ). The first axis may also be referred to as the fast axis. The second axis may also be referred to as the slow axis. The example in FIG. 1 schematically illustrates the divergence of the excitation light L0 on the slow axis.

[0035] 1, the wavelength separation filter 5 reflects the excitation light L0 toward the wavelength conversion member 4 and transmits the fluorescence L1 toward the exit opening 7a. The wavelength separation filter 5 is also called a dichroic mirror.

[0036] The wavelength separation filter 5 includes, for example, a dielectric multilayer film 51 and a substrate 52. The substrate 52 is a transparent plate-like member. The substrate 52 is positioned such that its thickness direction intersects with the optical axis AX1 of the optical system 6 at an angle of approximately 45 degrees. The dielectric multilayer film 51 is formed on the substrate 52.

[0037] For example, the dielectric multilayer film 51 has a structure in which thin dielectric films are repeatedly stacked. ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), tantalum oxide (Ta ２ O ５ ) and niobium oxide (Nb ２ O ３ ) is used. For example, by appropriately setting the thicknesses of the plurality of dielectric thin films that make up the dielectric multilayer film 51, it is possible to achieve a spectral transmittance that reflects the excitation light L0 in the dielectric multilayer film 51 and transmits the fluorescence L1. In other words, the function of the wavelength separation filter 5 is substantially realized by the dielectric multilayer film 51.

[0038] <1-4. Wavelength conversion member 4> The wavelength conversion member 4 contains a fluorescent material. The wavelength conversion member 4 contains a wavelength conversion material (i.e., a fluorescent material) that converts the excitation light L0 into blue light, such as BaMgAl１０ O １７ :Eu or (Sr, Ca, Ba) １０ (P.O. ４ ) ６ Cl ２ :Eu, (Sr, Ba) １０ (P.O. ４ ) ６ Cl ２ The wavelength conversion member 4 may contain, for example, (Sr, Ba, Ca) as a wavelength conversion material that converts the excitation light L0 into blue-green light. ５ (P.O. ４ ) ３ Cl:Eu,Sr ４ Al １４ O ２５ The wavelength conversion member 4 may contain, for example, SrSi as a wavelength conversion material that converts the excitation light L0 into green light. ２ (O, Cl) ２ N ２ :Eu, (Sr, Ba, Mg) ２ SiO ４ :Eu ２＋ , or ZnS:Cu, Al, Zn ２ SiO ４ The wavelength conversion member 4 may contain, for example, Y:Mn as a wavelength conversion material that converts the excitation light L0 into red light. ２ O ２ S: Eu, Y ２ O ３ :Eu, SrCaClAlSiN ３ :Eu ２＋ , CaAlSiN ３ : Eu or CaAlSi(ON) ３ The wavelength conversion member 4 may contain 3Ga as a wavelength conversion material that converts the excitation light L0 into light having a wavelength in the near-infrared region. ５ O １２ :Cr, etc. If the wavelength conversion member 4 contains multiple types of wavelength conversion materials corresponding to multiple colors of light, the wavelength conversion member 4 can emit fluorescence L1 with high color rendering. Specifically, if the excitation light L0 is light having a peak in the range of 380 nm to 415 nm and the wavelength conversion member 4 contains phosphors corresponding to red, green, and blue light, the color rendering of the fluorescence L1 can be particularly improved.

[0039] Furthermore, the wavelength conversion member 4 may contain a resin such as a binder for binding the phosphor particles together.

[0040] <1-5. Optical System 6> The lenses 61 are formed of a material containing at least one of glass, such as optical glass, and resin, such as acrylic resin. As shown in FIG. 1, each lens 61 may be a biconvex lens. Note that the lenses 61 are not limited to convex lenses, and may also be concave lenses or meniscus lenses. Furthermore, the lenses 61 may be spherical lenses or aspherical lenses.

[0041] When the surface 4a of the wavelength conversion member 4 on the lens 61A side is defined as the object plane, the optical system 6 forms an image of the object plane on a virtual image plane IS1. That is, in the example of Fig. 1, three lenses 61 can constitute an imaging optical system. In the illumination device 1, the surface 4a of the wavelength conversion member 4 has a conjugate relationship with the image plane IS1. Note that the term "conjugate relationship" here does not have a strict meaning; the portion on the exit aperture 7a side where the fluorescence L1 is most concentrated (the portion where the magnitude of the fluorescence L1 is smallest in a cross section perpendicular to the optical axis AX1 of the optical system 6) can be considered to be the image plane IS1.

[0042] The image plane IS1 may be located at the exit opening 7a, for example. The fluorescence L1 is collected at the image plane IS1 and emitted through the exit opening 7a into the illumination space S1. The image plane IS1 does not necessarily have to be located inside the exit opening 7a. The image plane IS1 may be located slightly offset from the exit opening 7a in the traveling direction of the fluorescence L1 passing through the exit opening 7a. In other words, the image plane IS1 may be located slightly inside the housing 7 relative to the exit opening 7a, or slightly toward the illumination space S1.

[0043] In the example of FIG. 1 , the lens 61A located closest to the wavelength conversion member 4 is a convex lens. Therefore, the lens 61A can guide the fluorescence L1, which has a large divergence angle and is emitted from the wavelength conversion member 4, to the subsequent lens 61B at a smaller divergence angle. Furthermore, in the example of FIG. 1 , the lens 61B is also a convex lens. Therefore, the lens 61B can guide the fluorescence L1, which diverges from the lens 61A, to the wavelength separation filter 5 while further reducing the divergence angle. The lens 61B may refract the fluorescence L1 so that the fluorescence L1 passes through the wavelength separation filter 5 in a state closer to parallel light. The lens 61C collects the fluorescence L1 that has passed through the wavelength separation filter 5 on the side of the exit opening 7a and emits it from the exit opening 7a at a predetermined luminous intensity distribution angle φ2.

[0044] The optical system 6 reduces the cross-sectional size (e.g., light diameter) of the fluorescence L1 at the image plane IS1, making it less likely that the fluorescence L1 will be reflected or scattered by the inner wall of the exit opening 7a of the housing 7, thereby realizing a more uniform and high-quality illumination space S1 with less glare. Furthermore, the presence of the illumination device 1 when viewed from outside the exit opening 7a can be reduced.

[0045] <1-6. Optical System 3> The optical system 3 is located between the light source 2 and the wavelength separation filter 5. Figures 2 and 3 are diagrams that schematically show an example of the configuration of the optical system 3. Figure 2 schematically shows an example of the configuration of the optical system 3 when viewed along the fast axis, and Figure 3 schematically shows an example of the configuration of the optical system 3 when viewed along the slow axis.

[0046] <1-6-1. Aspherical Lens 31> <1-6-1-1. Aspherical Surface 31a> The aspherical lens 31 is formed of a material containing at least one of glass, such as optical glass, and resin, such as acrylic resin. The aspherical lens 31 has an aspherical surface 31a and a surface 31b opposite to the aspherical surface 31a. In the examples of FIGS. 2 and 3, the surface 31b is the surface of the aspherical lens 31 facing the light source 2, and the aspherical surface 31a is the surface of the aspherical lens 31 opposite to the light source 2. In the examples of FIGS. 2 and 3, the aspherical surface 31a has a concave shape. The aspherical surface 31a may have a shape that is rotationally symmetric about the optical axis AX0.

[0047] 4A and 4B are graphs illustrating the shape of the aspherical surface 31a of the aspherical lens 31. FIG. 4A shows the sag z(h) at each position on the aspherical surface 31a, and FIG. 4B shows the curvature at each position on the aspherical surface 31a. In FIGS. 4A and 4B, the horizontal axis represents the distance h from the optical axis AX0. In FIG. 4A, the vertical axis represents the sag z(h), and in FIG. 4B, the vertical axis represents the curvature.

[0048] The graph in Figure 4(a) shows the relationship between the sag amount z(h) and the distance h, and therefore shows the shape of the aspherical surface 31a itself in a cross section including the optical axis AX0. The aspherical surface 31a may have a shape that follows, for example, one of the curves of a hyperbola in a cross section including the optical axis AX0. As a specific example, the aspherical surface 31a may have a shape that follows one of the hyperboloids of a two-sheet hyperboloid. For reference, in Figures 4(a) and 4(b), the dashed lines show graphs for a spherical surface having the same curvature as the curvature at the center of the aspherical surface 31a. The curvature of a circle is constant regardless of the distance h.

[0049] In the example of FIG. 4( b), in a predetermined circular region R1 including the center of the aspherical surface 31a, the curvature gradually decreases as the distance h increases. That is, the curvature monotonically decreases in the circular region R1. The predetermined circular region R1 may be, for example, a region concentric with the aspherical surface 31a and approximately 50% or less of the diameter of the aspherical surface 31a, in other words, approximately 50% or less of the effective diameter of the aspherical lens 31. Also, in the example of FIG. 4( b), the curvature gradually increases slightly as the distance h increases in an annular region R2 of the aspherical surface 31a located outside the circular region R1. That is, the curvature reaches its minimum value at the boundary between the circular region R1 and the annular region R2. In the aspherical surface 31a of this aspherical lens 31, the maximum curvature may be at least twice, at least five times, at least ten times, or at least twenty times the minimum curvature.

[0050] Figure 5 is also a graph for explaining the shape of the aspherical surface 31a. Figure 5(a) is a graph showing the relationship between the angle θ (see also Figures 2 and 3) formed by the surface normal and the optical axis AX0 at each position within the aspherical surface 31a and the distance h. Figure 5(b) is a graph showing the relationship between the first-order differential value of the angle θ with respect to the distance h and the distance h. Figure 5(c) is a graph showing the relationship between the second-order differential value of the angle θ with respect to the distance h and the distance h. Note that, for reference, Figure 5 also shows a graph for a spherical surface having the same curvature as the curvature at the center of the aspherical surface 31a, shown by a dashed line.

[0051] In the example of Figure 5(b), the first-order derivative of the angle θ for the spherical surface monotonically increases with increasing distance h. In contrast, the first-order derivative of the angle θ for the aspherical surface 31a gradually decreases as the distance h increases, approximately within a circular region R1. In other words, the first-order derivative of the angle θ monotonically decreases within the circular region R1. Also, in the example of Figure 5(b), the first-order derivative of the angle θ gradually increases slightly with increasing distance h, approximately within an annular region R2. For the aspherical surface 31a of this aspherical lens 31, the maximum value of the first-order derivative of the angle θ may be at least two times, five times, ten times, or even twenty times the minimum value.

[0052] In the example of Figure 5(c), the second-order derivative of the angle θ for the spherical surface also monotonically increases with increasing distance h. In contrast, the second-order derivative of the angle θ for the aspherical surface 31a decreases with increasing distance h, reaches a minimum value (local minimum value), and then increases. In other words, the graph showing the relationship between the second-order derivative of the angle θ and the distance h has a local minimum value. More specifically, the graph showing the relationship between the second-order derivative of the angle θ and the distance h has a local minimum value in a region that is 30% or less of the effective diameter of the aspherical lens 31. Furthermore, while the second-order derivative of the angle θ for the spherical surface is positive regardless of the distance h, the second-order derivative of the angle θ for the aspherical surface 31a is negative throughout the entire region that is 30% or less of the effective diameter of the aspherical lens 31.

[0053] Referring also to FIG. 2 , excitation light L0 is incident on the aspherical surface 31 a of the aspherical lens 31. In FIG. 2 , the intensity distribution of the excitation light L0 immediately before it is incident on the aspherical surface 31 a is schematically shown to the left of the aspherical surface 31 a, and the cross-sectional shape of the excitation light L0 is schematically shown below the intensity distribution. Hereinafter, the central light of the excitation light L0 will be referred to as central light L0a. The central light L0a is a portion of the excitation light L0 whose intensity is, for example, 50% or more of the peak intensity. Hereinafter, the light of the excitation light L0 that is outside the central light L0a will be referred to as peripheral light L0b. The peripheral light L0b is a portion of the excitation light L0 whose intensity is, for example, less than 50% of the peak intensity.

[0054] In the following description, the region of the aspherical surface 31a onto which the central ray L0a is incident is referred to as the first central portion 31aa, and the region onto which the peripheral ray L0b is incident is referred to as the first non-central portion 31ab. The first central portion 31aa is a portion of the aspherical surface 31a closer to the optical axis AX0 than the first non-central portion 31ab.

[0055] The first central portion 31aa is, for example, a region within the circular region R1 (see also FIG. 4B). That is, the outer peripheral edge of the first central portion 31aa is located within the circular region R1, for example. The outer peripheral edge of the first central portion 31aa is also the boundary between the first central portion 31aa and the first non-central portions 31ab. The first non-central portions 31ab may also be a region within the circular region R1 (see also FIG. 4B). That is, the outer peripheral edge of the first non-central portions 31ab may also be located within the circular region R1. In this case, the curvature at each position of the first central portion 31aa and the first non-central portions 31ab monotonically decreases from the center toward the outside.

[0056] The curvature of the first central portion 31aa is greater than the curvature of the first non-central portion 31ab. For example, the average curvature of the first central portion 31aa is greater than the average curvature of the first non-central portion 31ab. Furthermore, the minimum curvature of the first central portion 31aa may be greater than the maximum curvature of the first non-central portion 31ab.

[0057] Because the curvature of the first central portion 31aa is relatively large, the central light L0a is refracted at the first central portion 31aa with a greater refractive power (see also FIG. 2 ). Therefore, the divergence angle of the central light L0a that passes through the aspherical lens 31 increases. In other words, the central light L0a diverges more as it passes through the aspherical lens 31. Here, the divergence angle of the central light L0a increases more as it passes through the center. On the other hand, because the curvature of the first non-central portion 31ab is relatively small, the peripheral light L0b is refracted at the first non-central portion 31ab with a smaller refractive power. Therefore, the divergence angle of the peripheral light L0b does not increase as much as the increase in the divergence angle of the central light L0a. In other words, the peripheral light L0b diverges less as it travels. Therefore, the density of the light rays on the central side decreases relatively as it moves away from the aspherical lens 31, and the density of the light rays on the peripheral side increases relatively as it moves away from the aspherical lens 31.

[0058] Therefore, in the intensity distribution of the excitation light L0, the width of the central light L0a, whose intensity is 50% or more of the peak intensity, becomes relatively wider as the distance from the aspherical lens 31 increases, and the width of the peripheral light L0b, whose intensity is less than 50% of the peak intensity, becomes relatively narrower. In other words, the intensity distribution becomes flatter.

[0059] 1 , the excitation light L0 from the aspherical lens 31 passes through the cylindrical lens 32, the wavelength separation filter 5, the lens 61B, and the lens 61A in this order, and is incident on the wavelength conversion member 4. Here, the shape of the aspherical surface 31 a of the aspherical lens 31 can be designed so that the intensity distribution of the excitation light L0 on the surface 4 a of the wavelength conversion member 4 has a top hat shape (in other words, a trapezoidal shape).

[0060] 6A and 6B are diagrams schematically illustrating an example of the intensity distribution of the excitation light L0. Fig. 6A shows an example of the intensity distribution of the excitation light L0 immediately after the light source 2. In other words, Fig. 6A shows an example of the intensity distribution of the excitation light L0 between the light source 2 and the optical system 3. Fig. 6B shows an example of the intensity distribution of the excitation light L0 in the wavelength conversion member 4. In Fig. 6B, the intensity distribution of the excitation light L0 immediately after the light source 2 is indicated by a two-dot chain line.

[0061] 6( a), the intensity distribution of the excitation light L0 immediately after the light source 2 has a single mountain-like shape. Hereinafter, the width of the region where the intensity is 90% or more of the peak intensity will be referred to as a first width D1, and the width of the region where the intensity is 50% or more of the peak intensity will be referred to as a second width D2. In this intensity distribution, the ratio of the first width D1 to the second width D2 (= D1 / D2) may be, for example, 0.5 or less.

[0062] 6(b), the intensity distribution of the excitation light L0 in the wavelength conversion member 4 has a top hat shape. In other words, the intensity distribution has a single trapezoidal shape. In this intensity distribution, the ratio of the first width D1 to the second width D2 (= D1 / D2) may be 0.7 or more. In other words, the aspherical lens 31 refracts the excitation light L0 having a ratio of 0.5 or less, thereby allowing the excitation light L0 having a ratio of 0.7 or more to be incident on the surface 4a of the wavelength conversion member 4.

[0063] Next, a specific example of the shape of the aspherical surface 31a for flattening the intensity distribution of the excitation light L0 will be further described. The shape of the aspherical surface 31a may be expressed by the following equation.

[0064]

[0065] Here, z(h) represents the amount of sag, k represents the conic coefficient, R0 represents the radius of curvature at the center of the aspheric surface 31a, and An (n is an even number) represents the coefficient of a higher-order term.

[0066] FIG. 7 is a graph illustrating the shape of the aspherical surface 31a corresponding to each of a plurality of conic coefficients k. FIG. 7(a) is a graph illustrating the relationship between the sag amount z(h) of the aspherical surface 31a and the distance h, and FIG. 7(b) is a graph illustrating the relationship between the second derivative of the angle θ and the distance h. FIG. 7(a) shows graphs Gz1 to Gz7. Graphs Gz1 to Gz7 respectively show the relationship between the sag amount z(h) and the distance h when the conic coefficient k is 0, -1, -5, -10, -20, -40, and -60. FIG. 7(b) shows graphs Gθ1 to Gθ7. Graphs Gθ1 to Gθ7 respectively show the relationship between the second derivative of the angle θ and the distance h when the conic coefficient k is 0, -1, -5, -10, -20, -40, and -60. In FIG. 7B, the minimum values ​​of the graph showing the relationship between the second derivative of the angle θ and the distance h are indicated by open circles.

[0067] 7A, the smaller the Conic coefficient k, the smaller the curvature of the outer periphery of the aspherical surface 31a. In other words, when the Conic coefficient k is reduced, the curvature of the aspherical surface 31a gradually decreases toward the outer periphery, and the outer periphery of the aspherical surface 31a approaches a linear shape in a cross section including the optical axis AX0. In other words, the outer periphery of the aspherical surface 31a approaches the shape of a cone side.

[0068] On the other hand, the curvature of the central portion of the aspherical surface 31a does not become so small compared to the outer periphery even if the Conic coefficient k becomes small.

[0069] Therefore, by reducing the Conic coefficient k, the aspherical lens 31 can effectively reduce the increase in the spread angle of the peripheral light L0b of the excitation light L0 while maintaining the effect of increasing the spread angle of the central light L0a of the excitation light L0. As a result, the aspherical lens 31 can more appropriately flatten the intensity distribution of the excitation light L0.

[0070] The Conic coefficient k may be, for example, not less than −60 and not more than −3. This allows the aspherical lens 31 to more appropriately flatten the intensity distribution of the excitation light L0 when the ratio of the first width D1 to the second width D2 is 0.5 or less. Furthermore, the Conic coefficient k may be not less than −60 and not more than −10, not more than −60 and not more than −20, or not more than −45 and not more than −35. The narrower the range that is applied within the above range, the more appropriately the aspherical lens 31 can flatten the intensity distribution of the excitation light L0.

[0071] Furthermore, it is preferable that the excitation light L0 is incident on a range of 30% or less of the effective diameter of the aspherical surface 31a of the aspherical lens 31. When the Conic coefficient k is in the above range, the aspherical lens 31 can further appropriately flatten the intensity distribution.

[0072] As can be seen from Figure 7(b), the smaller the Conic coefficient k, the closer the position of the minimum value is to the center of the aspherical surface 31a. Furthermore, the smaller the Conic coefficient k, the smaller the minimum value. As can be seen from Figure 7(b), the minimum value may be 30% or less of the effective diameter of the aspherical lens 31, or may be 25% or less. In this case, the Conic coefficient k is -3 or less.

[0073] Next, the technical significance of the aspherical surface 31a having a concave shape will be explained. In the example of FIG. 1 , the excitation light L0 transmitted through the aspherical lens 31 spreads toward the lens 61B, is refracted by the convex lenses 61B and 61A, and is focused on the wavelength conversion member 4. While the cross-sectional size of the excitation light L0 is reduced by the convex lenses 61B and 61A, the aspherical surface 31a of the concave aspherical lens 31 increases the cross-sectional size of the excitation light L0 incident on the lens 61B. This allows the excitation light L0 to be incident on the surface 4a of the wavelength conversion member 4 over a sufficiently large incident area. This allows the wavelength conversion member 4 to emit fluorescence L1 over a wider range.

[0074] <1-6-1-2. Surface 31b Opposite to Aspherical Surface 31a> In the examples shown in FIGS. 1 to 3, surface 31b of aspherical lens 31 has a convex shape. Surface 31b may have a shape that is rotationally symmetric about optical axis AX0. In the examples shown in FIGS. 1 to 3, aspherical surface 31a has a concave shape and opposite surface 31b has a convex shape, aspherical lens 31 is a so-called meniscus lens. Because surface 31b of aspherical lens 31 has a convex shape, surface 31b can refract excitation light L0 so as to reduce the divergence angle of excitation light L0. In other words, while the concave aspherical surface 31a of aspherical lens 31 increases the divergence angle of excitation light L0, the convex surface 31b reduces the divergence angle of excitation light L0. Therefore, the amount of change in the divergence angle of excitation light L0 due to transmission through aspherical lens 31 can be reduced. This reduces the possibility that the incident area of ​​the excitation light L0 on the surface 4a of the wavelength conversion member 4, which is distant from the optical system 3, will unnecessarily widen.

[0075] The surface 31b of the aspherical lens 31 may be spherical or aspherical. If the surface 31b is aspherical, the curvature of the second central portion 31ba of the surface 31b may be greater than the curvature of the second non-central portion 31bb of the surface 31b. The curvature of the surface 31b may monotonically decrease from the center toward the outside in a region including both the second central portion 31ba and the second non-central portion 31bb. As a specific example, the surface 31b may have a shape that follows a hyperbolic surface. For example, central light L0a of the excitation light L0 may be incident on the second central portion 31ba, and peripheral light L0b of the excitation light L0 may be incident on the second non-central portion 31bb.

[0076] The shape of surface 31b may be the same as that of aspherical surface 31a. That is, a graph showing the relationship between the second derivative of angle θ and distance h for surface 31b may have a minimum value. The minimum value may be located within a region of 30% or less of the effective diameter of aspherical lens 31. Conic coefficient k may be within the above-mentioned range.

[0077] The central light L0a is refracted by the surface 31b so as to reduce its divergence angle, while the peripheral light L0b is refracted by the surface 31b so that its divergence angle is not significantly reduced compared to the central light L0a. This allows the central light L0a to be incident on a region of the aspherical surface 31a with a greater curvature. In other words, because the curvature of the aspherical surface 31a is greater toward its center, the central light L0a is incident on the first central portion 31aa, which has a greater curvature. This allows the aspherical surface 31a to refract the more intense central light L0a at the first central portion 31aa, which has a greater curvature, thereby increasing the divergence angle of the central light L0a. This allows the central light L0a of the excitation light L0 to be broadened, resulting in a flatter intensity distribution.

[0078] 1 to 3, the optical system 3 further includes a cylindrical lens 32. The cylindrical lens 32 is formed of a material containing at least one of glass, such as optical glass, and resin, such as acrylic resin. In the example of FIG. 1, the cylindrical lens 32 is located between the aspherical lens 31 and the wavelength separation filter 5.

[0079] The cylindrical lens 32 adjusts the aspect ratio of the cross-sectional shape of the excitation light L0. In other words, the cylindrical lens 32 can adjust the ratio between the width of the excitation light L0 on the fast axis and the width of the excitation light L0 on the slow axis. The width of the light can be adjusted, for example, by adjusting the ratio of the peak intensity e ２ The cylindrical lens 32 may be configured to adjust the aspect ratio of the excitation light L0 so that the aspect ratio of the cross-sectional shape of the excitation light L0 on the surface 4 a of the wavelength conversion member 4 approaches the aspect ratio of the surface 4 a of the wavelength conversion member 4.

[0080] In the examples shown in FIGS. 2 and 3 , the cylindrical lens 32 is a plano-convex lens. That is, the cylindrical lens 32 has a convex surface 32 a and a flat surface 32 b. In the examples shown in FIGS. 2 and 3 , the flat surface 32 b is located closer to the light source 2 than the convex surface 32 a. In other words, the flat surface 32 b is located closer to the aspherical lens 31 than the convex surface 32 a. The convex surface 32 a may be spherical. The cylindrical lens 32 is oriented such that its power direction is along the fast axis. As a result, in a cross section parallel to the slow axis and the optical axis AX0 (see FIG. 2 ), the divergence angle of the excitation light L0 changes little before and after the cylindrical lens 32. In a cross section parallel to the fast axis and the optical axis AX0 (see FIG. 3 ), the divergence angle of the excitation light L0 is reduced by the cylindrical lens 32. This reduces the difference between the fast axis and the slow axis in the divergence angle of the excitation light L0 transmitted through the cylindrical lens 32. Therefore, the aspect ratio of the cross-sectional shape of the excitation light L0 approaches 1 as it moves away from the cylindrical lens 32.

[0081] As shown in Figures 2 and 3, the aspherical lens 31 and the cylindrical lens 32 may be in contact with each other. As shown in Figures 2 and 3, the outer circumferential portion 31ac of the aspherical surface 31a of the aspherical lens 31 may be a flat surface perpendicular to the optical axis AX0. The outer circumferential portion 31ac may be a portion located outside the first non-central portion 31ab and may not be a portion onto which the excitation light L0 is incident. The outer circumferential portion 31ac of the aspherical lens 31 may be in contact with the flat surface 32b of the cylindrical lens 32, or may be bonded to the flat surface 32b of the cylindrical lens 32. This facilitates positioning of the aspherical lens 31 relative to the cylindrical lens 32.

[0082] 1, the illumination device 1 may include a holder 721 that integrally holds the optical system 3. The holder 721 integrally holds the aspherical lens 31 and the cylindrical lens 32, and is attached to the housing 72. The holder 721 may, for example, clamp the outer peripheries of the aspherical lens 31 and the cylindrical lens 32 in the direction along the optical axis AX0.

[0083] According to this, by attaching the holder 721 to the housing 72, the aspherical lens 31 and the cylindrical lens 32 can be stored in the housing 72. This assembly work is relatively easy. Note that the holder 721 may be part of the housing 72.

[0084] 2. Second Embodiment 2-1. Schematic Configuration of Illumination Device 1 FIG. 8 is a diagram schematically illustrating an example of the configuration of an illumination device 1 according to a second embodiment. Hereinafter, the illumination device 1 according to the second embodiment will be referred to as illumination device 1A. The illumination device 1A differs from the illumination device 1 according to the first embodiment in the position of the optical elements. In the illumination device 1A, the light source 2, the optical system 3, the wavelength separation filter 5, the lens 61B, the lens 61A, and the wavelength conversion member 4 are arranged in this order in the second direction, and the wavelength separation filter 5 and the exit opening 7a are arranged in this order in the first direction intersecting the second direction. In the example of FIG. 8, the first direction and the second direction are orthogonal to each other. When the illumination device 1A is installed on a ceiling, the illumination device 1A is installed on the ceiling with the first direction aligned vertically. In this case, the second direction is aligned horizontally.

[0085] The excitation light L0 from the light source 2 is incident on the optical system 3. As will be described later, the optical system 3 adjusts the intensity distribution of the excitation light L0. The excitation light L0 from the optical system 3 is incident on the wavelength separation filter 5. The wavelength separation filter 5 transmits the excitation light L0 and guides it to the wavelength conversion member 4. In the example of FIG. 8 , the excitation light L0 is transmitted through lenses 61B and 61A of the optical system 6 and is incident on the wavelength conversion member 4.

[0086] The optical system 3 includes an aspherical lens 31. The aspherical lens 31 refracts each ray of the excitation light L0 to flatten the intensity distribution of the excitation light L0. As a specific example, the aspherical lens 31 refracts the excitation light L0 so that the intensity distribution of the excitation light L0 in the wavelength conversion member 4 has a top hat shape. This allows more uniform excitation light L0 to be incident on the wavelength conversion member 4, allowing the wavelength conversion member 4 to emit more uniform fluorescence L1.

[0087] 8, the fluorescence L1 from the wavelength conversion member 4 passes through the lenses 61A and 61B and enters the wavelength separation filter 5. The wavelength separation filter 5 reflects the fluorescence L1 and guides it to the exit opening 7a.

[0088] The optical system 6 is located on the path of the fluorescence L1 from the wavelength conversion member 4 to the exit opening 7a, and emits the fluorescence L1 from the exit opening 7a at a predetermined luminous intensity distribution angle while forming an image of the fluorescence L1 on a virtual image plane IS1 on the exit opening 7a side. The optical system 6 includes one or more lenses 61 located on the path. In the example of FIG. 8 , multiple lenses 61 are located, and more specifically, three lenses 61A to 61C are located as the multiple lenses 61. The lenses 61A and 61B are located between the wavelength conversion member 4 and the wavelength separation filter 5. The lens 61A is located closer to the wavelength conversion member 4 than the lens 61B. The lens 61C is located between the wavelength separation filter 5 and the exit opening 7a.

[0089] In the lighting device 1A, the aspherical lens 31 also flattens the intensity distribution of the excitation light L0. This allows the lighting device 1A to emit fluorescence L1 with less unevenness into the illumination space S1. Furthermore, in the lighting device 1A, the wavelength conversion member 4, lens 61A, lens 61B, wavelength separation filter 5, optical system 3, and light source 2 are aligned along the second direction, while the wavelength separation filter 5 and lens 61C are aligned along the first direction. This reduces the number of optical components aligned along the first direction, allowing the size of the lighting device 1A in the first direction to be reduced. Therefore, the lighting device 1A can be easily installed in a low-height space above the ceiling.

[0090] <2-2. Aspherical Lens 31> In the example of Fig. 8, the aspherical lens 31 is a biconvex lens. That is, both the aspherical surface 31a of the aspherical lens 31 and the surface 31b opposite thereto have a convex shape. In the example of Fig. 8, the aspherical surface 31a is located closer to the light source 2 than the surface 31b. The surface 31b may be spherical.

[0091] Fig. 9 is a diagram illustrating the shape of the aspherical surface 31a of the aspherical lens 31. In the example of Fig. 9, the aspherical surface 31a is located on the opposite side from the light source 2, but even if the aspherical surface 31a is located on the light source 2 side, the principle of flattening the intensity distribution by the aspherical lens 31 is the same.

[0092] As shown in FIG. 9 , the excitation light L0 is refracted by the aspherical surface 31a. Because the aspherical surface 31a has a convex shape, the divergence angle of the excitation light L0 is reduced by passing through the aspherical lens 31. In the example of FIG. 9 , the excitation light L0 that passes through the aspherical lens 31 narrows as it travels and is collected at the condenser BW1. In other words, the excitation light L0 has a condensing portion (i.e., the condenser BW1). The excitation light L0 then travels forward from the condenser BW1 while diverging again. Referring to FIG. 8 , the condenser BW1 is located between the aspherical lens 31 and the wavelength conversion member 4. As a more specific example, the condenser BW1 is located between the aspherical lens 31 and the lens 61B. The condenser BW1 may be located between the aspherical lens 31 and the wavelength separation filter 5, on the wavelength separation filter 5, or between the wavelength separation filter 5 and the lens 61B.

[0093] 10 is a graph illustrating the shape of the aspherical surface 31a of the aspherical lens 31. Fig. 10(a) shows the sag z(h) at each position on the aspherical surface 31a, and Fig. 10(b) shows the curvature at each position on the aspherical surface 31a. For reference, Fig. 10 also shows a graph of a spherical surface having the same curvature as the curvature at the center of the aspherical surface 31a, indicated by a dashed line.

[0094] In the example of Figure 10(b), in a predetermined circular region R1 including the center of the aspherical surface 31a, the curvature gradually decreases as the distance h increases. That is, the curvature monotonically decreases in the circular region R1. In Figure 10(b), the diameter of the circular region R1 is approximately 60% of the effective diameter of the aspherical lens 31. Also in the example of Figure 10(b), the curvature gradually increases as the distance h increases in an annular region R2 of the aspherical surface 31a located outside the circular region R1. That is, the curvature reaches its minimum value at the boundary between the circular region R1 and the annular region R2. In the aspherical surface 31a of this aspherical lens 31, the maximum curvature may be more than twice the minimum curvature.

[0095] Fig. 11 is also a graph for explaining the shape of the aspherical surface 31a. Fig. 11(a) is a graph showing the relationship between the angle θ and the distance h. Fig. 11(b) is a graph showing the relationship between the first-order differential value of the angle θ with respect to the distance h and the distance h. Fig. 11(c) is a graph showing the relationship between the second-order differential value of the angle θ with respect to the distance h and the distance h. Note that in Fig. 11 as well, the dashed line shows the graph for a spherical surface having the same curvature as the curvature at the center of the aspherical surface 31a.

[0096] In the example of Figure 11(b), the first-order derivative of the angle θ for the spherical surface monotonically increases with increasing distance h. In contrast, the first-order derivative of the angle θ for the aspherical surface 31a gradually decreases as the distance h increases, approximately within a circular region R1. In other words, the first-order derivative of the angle θ monotonically decreases within the circular region R1. Also, in the example of Figure 11(b), the first-order derivative of the angle θ gradually increases slightly with increasing distance h, approximately within an annular region R2. For the aspherical surface 31a of this aspherical lens 31, the maximum value of the first-order derivative of the angle θ may be more than twice the minimum value of the curvature.

[0097] In the example of Figure 11(c), the second-order derivative of the angle θ for the spherical surface also monotonically increases with increasing distance h. In contrast, the second-order derivative of the angle θ for the aspherical surface 31a decreases with increasing distance h, reaches a minimum value (local minimum value), and then increases. In other words, the graph showing the relationship between the second-order derivative of the angle θ and the distance h has a local minimum value. More specifically, the graph showing the relationship between the second-order derivative of the angle θ and the distance h has a local minimum value in a region that is 30% or less of the effective diameter of the aspherical lens 31. Furthermore, while the second-order derivative of the angle θ for the spherical surface is positive regardless of the distance h, the second-order derivative of the angle θ is negative throughout the entire region that is 30% or less of the effective diameter of the aspherical lens 31.

[0098] 9, excitation light L0 is incident on the aspherical surface 31a of the aspherical lens 31. In Fig. 9, the intensity distribution of the excitation light L0 immediately before it is incident on the aspherical surface 31a is shown schematically below the aspherical lens 31, and the cross-sectional shape of the excitation light L0 is shown schematically to the right of the intensity distribution.

[0099] The central ray L0a is incident on the first central portion 31aa of the aspherical surface 31a, and the peripheral ray L0b is incident on the first non-central portion 31ab of the aspherical surface 31a. The first central portion 31aa is, for example, a region within the circular region R1 (see also FIG. 10B). That is, the outer peripheral edge of the first central portion 31aa is, for example, located within the circular region R1. The first non-central portion 31ab may also be a region within the circular region R1 (see also FIG. 10B). That is, the outer peripheral edge of the first non-central portion 31ab may also be located within the circular region R1. In this case, the curvature at each position on the first central portion 31aa and the first non-central portion 31ab monotonically decreases from the center toward the outside.

[0100] The curvature of the first central portion 31aa is greater than the curvature of the first non-central portion 31ab. For example, the average curvature of the first central portion 31aa is greater than the average curvature of the first non-central portion 31ab. Furthermore, the minimum curvature of the first central portion 31aa may be greater than the maximum curvature of the first non-central portion 31ab.

[0101] Because the curvature of the first central portion 31aa is relatively large, the central light L0a is refracted with a greater refractive power. Therefore, the central light L0a is focused at a position closer to the aspherical lens 31 and travels while diverging forward from the focusing position. Here, the light rays of the central light L0a closer to the center are refracted with a greater refractive power. Therefore, the light rays closer to the center are focused at a position closer to the aspherical lens 31. In the example of Figure 9, the two central light rays that are focused at the position closest to the aspherical lens 31 are shown by dashed lines.

[0102] On the other hand, because the curvature of the first non-central portion 31ab is relatively small, the peripheral light L0b is refracted with a smaller refractive power. Therefore, the peripheral light L0b is focused at a position farther from the aspherical lens 31 and travels while spreading forward from the focusing position. Here, the light rays of the peripheral light L0b closer to the outer periphery are refracted with a smaller refractive power. Therefore, the light rays closer to the outer periphery are focused at a position farther from the aspherical lens 31. In the example of Figure 9, the two peripheral light rays that are focused at the position farthest from the aspherical lens 31 are indicated by dashed dotted lines.

[0103] Since light rays focused at a position close to the aspherical lens 31 begin to spread from a position close to the aspherical lens 31, the density of light rays near the center decreases at a position forward of the focusing portion BW1. Conversely, the density of light rays near the periphery increases. In other words, the width of central light L0a, whose intensity is 50% or more of the peak intensity, becomes relatively wider as it moves forward from the focusing portion BW1, and the width of peripheral light L0b, whose intensity is less than 50% of the peak intensity, becomes relatively narrower. This results in a flatter intensity distribution.

[0104] 8 , the excitation light L0 from the aspherical lens 31 passes through the wavelength separation filter 5, the lens 61B, and the lens 61A in this order, and is incident on the wavelength conversion member 4. Here, the shape of the aspherical surface 31 a of the aspherical lens 31 can be designed so that the intensity distribution of the excitation light L0 on the surface 4 a of the wavelength conversion member 4 has a top hat shape.

[0105] The Conic coefficient k, which is one of the indices indicating the shape of the aspherical surface 31a of the aspherical lens 31, may be -60 or more and -3 or less, as in the first embodiment. This allows the aspherical lens 31 to more appropriately flatten the intensity distribution of the excitation light L0 in which the ratio of the first width D1 to the second width D2 is 0.5 or less. Furthermore, the Conic coefficient k may be -60 or more and -10 or less, -60 or more and -20 or less, or -45 or more and -35 or less.

[0106] Next, the technical significance of focusing the excitation light L0 at the focusing unit BW1 will be described. According to this, the excitation light L0 travels while diverging forward of the focusing unit BW1. Therefore, the excitation light L0 can be sufficiently diverged just before the lens 61B, and even if the excitation light L0 is reduced in size by the convex lenses 61A and 61B, it can be incident on the surface 4a of the wavelength conversion member 4 over a sufficiently large incident area.

[0107] 8, the aspherical lens 31 focuses the excitation light L0 at the focusing portion BW1, and therefore has a large refractive power. For example, the radius of curvature R0 at the center of the aspherical surface 31a is larger than the radius of curvature R0 of the aspherical surface 31a according to the first embodiment. When the excitation light L0 is incident on such an aspherical lens 31 with a large difference between the width of the slow axis and the width of the fast axis, the flattening of the intensity distribution by the aspherical surface 31a is unlikely to be effective to the same extent on both the fast axis and the slow axis. As a result, it is difficult to appropriately flatten the intensity distribution, particularly on the slow axis.

[0108] Therefore, in the example of Figure 8, the cylindrical lens 32 is located between the light source 2 and the aspherical lens 31. The cylindrical lens 32 refracts the excitation light L0 so that the aspect ratio of the excitation light L0 approaches 1. In other words, the aspect ratio of the excitation light L0 immediately after the cylindrical lens 32 is closer to 1 than the aspect ratio of the excitation light L0 immediately before the cylindrical lens 32. Therefore, the excitation light L0 can be incident on the aspherical lens 31 in a state where the difference between the width of the fast axis and the width of the slow axis of the excitation light L0 is reduced. In Figure 9, the aspect ratio of the cross-sectional shape of the excitation light L0 incident on the aspherical lens 31 is close to 1.

[0109] This allows the aspherical lens 31 to more appropriately flatten the intensity distribution on both the fast axis and the slow axis.

[0110] 2-4. Other Examples of Aspherical Lens 31 FIG. 12 is a diagram illustrating another example of the aspherical surface 31a of the aspherical lens 31. In the example of FIG. 12, the aspherical surface 31a also has a convex shape, so the divergence angle of the excitation light L0 is reduced upon transmission through the aspherical lens 31. In the example of FIG. 12, the excitation light L0 that has transmitted through the aspherical lens 31 narrows as it travels. However, the excitation light L0 is incident on the surface 4a of the wavelength conversion member 4 before the focusing portion where the beam diameter is smallest. In other words, when the aspherical lens 31 of FIG. 12 is used, the excitation light L0 does not have the focusing portion BW1 between the aspherical lens 31 and the wavelength conversion member 4.

[0111] 12, the curvature of the first central portion 31aa of the aspherical surface 31a is smaller than the curvature of the first non-central portion 31ab. The curvature of the aspherical surface 31a may monotonically increase from the center toward the outside in the region including the first central portion 31aa and the first non-central portion 31ab.

[0112] Because the curvature of the first central portion 31aa is relatively small, the central light L0a is refracted with a smaller refractive power. Therefore, the central light L0a is focused at a position farther from the aspherical lens 31. Here, the closer to the center of the central light L0a, the smaller the refractive power that is refracted. Therefore, the closer to the center, the farther the light ray is focused at a position farther from the aspherical lens 31. In the example of Figure 12, the two central light rays that are focused at the position farthest from the aspherical lens 31 are indicated by dashed lines, and a virtual focusing position Pa of the two light rays is schematically shown.

[0113] On the other hand, because the curvature of the first non-central portion 31ab is relatively large, the peripheral light L0b is refracted with a greater refractive power. As a result, the peripheral light L0b is focused at a position closer to the aspherical lens 31. Here, the closer a ray of the peripheral light L0b is to the outer periphery, the greater the refractive power it is refracted with. As a result, the closer a ray is to the outer periphery, the closer it is to the aspherical lens 31 it is focused at a position closer to the aspherical lens 31. In the example of Figure 12, two peripheral light rays that focus at a position closest to the aspherical lens 31 are indicated by dashed dotted lines, and a virtual focusing position Pb of the two light rays is schematically shown.

[0114] Because light rays close to the center are focused farther from the aspherical lens 31, the density of light rays close to the center is relatively low between the aspherical lens 31 and the focusing position Pb. On the other hand, light rays close to the periphery are focused closer to the aspherical lens 31, so the density of light rays close to the periphery is high. In other words, the width of the central light L0a, whose intensity is 50% or more of the peak intensity, becomes relatively wider toward the front of the aspherical lens 31, and the width of the peripheral light L0b, whose intensity is less than 50% of the peak intensity, becomes relatively narrower. Therefore, the intensity distribution becomes flatter.

[0115] 8 , the excitation light L0 from the aspherical lens 31 passes through the wavelength separation filter 5, the lens 61B, and the lens 61A in this order, and is incident on the wavelength conversion member 4. Here, the shape of the aspherical surface 31 a of the aspherical lens 31 can be designed so that the intensity distribution of the excitation light L0 on the surface 4 a of the wavelength conversion member 4 has a top hat shape.

[0116] It should be noted that the shape of the aspherical surface 31a of the aspherical lens 31 according to the second embodiment can be applied to the first embodiment, and the shape of the aspherical surface 31a of the aspherical lens 31 according to the first embodiment can also be applied to the second embodiment.

[0117] 3. Third Embodiment FIG. 13 is a diagram schematically illustrating an example of the configuration of an illumination device 1 according to a third embodiment. Hereinafter, the illumination device 1 in FIG. 13 will be referred to as illumination device 1B. The illumination device 1B differs from the illumination device 1 according to the first embodiment in the presence or absence of a light-reducing structure 8. The light-reducing structure 8 is located on at least a portion of the inner wall of the housing 7. More specifically, the light-reducing structure 8 is located on at least a portion of the inner wall of the housing 71. In the example of FIG. 13 , the housing 71 includes a cylindrical portion 73 that surrounds the path of the fluorescence L1. The cylindrical portion 73 houses lenses 61A, 61B, a wavelength separation filter 5, and a lens 61C. An exit opening 7a is formed at the end of the cylindrical portion 73. Furthermore, an opening 74 is formed on the side of the cylindrical portion 73, allowing the excitation light L0 from the light source 2 to pass through. 13 , the light reducing structure 8 is located on at least a portion of the inner wall of the cylindrical portion 73. As a more specific example, the light reducing structure 8 is located on the inner wall of the cylindrical portion 73 between the lens 61B and the wavelength separation filter 5, between the wavelength separation filter 5 and the lens 61C, and between the lens 61C and the emission opening 7a. As shown in FIG. 13 , the light reducing structure 8 does not have to be located on the inner wall of the cylindrical portion 73 between the lens 61A and the lens 61B. The light reducing structure 8 may be formed on the entire circumference of the inner wall of the cylindrical portion 73. Here, "the entire circumference" refers to the entire circumference of the inner wall in a cross section perpendicular to the optical axis AX1.

[0118] Light (hereinafter referred to as unwanted light) generated by reflection or scattering of the fluorescence L1 inside the housing 71 may be incident on the light reducing structure 8. As will be described later, the light reducing structure 8 reduces the possibility that the unwanted light will be emitted from the exit opening 7 a into the illumination space S1.

[0119] The light reducing structure 8 includes, for example, a reflection reduction portion 81. The reflection reduction portion 81 may include an absorbing film having a high absorptance for the fluorescence L1. The absorptance may be, for example, 50% or more, 60% or more, 80% or more, or 90% or more. The reflection reduction portion 81 may have a high absorptance for the entire wavelength range of the fluorescence L1, or may have a high absorptance for the peak wavelength. The absorptance of the reflection reduction portion 81 for the fluorescence L1 is higher than the absorptance of the inner wall of the housing portion 71 where the light reducing structure 8 is not located.

[0120] The reflection reduction portion 81 can be formed by, for example, blackening the inner wall of the housing 71. As a specific example, the reflection reduction portion 81 is formed on the inner wall of the housing 71 by blackening such as chemical conversion coating, plating, or painting. As the blackening, a matte blackening process or a glossy blackening process may be adopted. The reflection reduction portion 81 is made of a black material. The material includes, for example, at least one of a black metal, a black metal oxide film, and a black resin.

[0121] Alternatively, the reflection reduction portion 81 may include a dielectric multilayer film. The dielectric multilayer film has, for example, a structure in which a plurality of dielectric thin films are stacked. Examples of the dielectric include titanium oxide (TiO ２ ), SiO ２ , niobium pentoxide (Nb ２ O ５ ), tantalum pentoxide (Ta ２ O ５ ) and magnesium fluoride (MgF ２ Such a dielectric multilayer film may be called a low-reflection film or an anti-reflection film.

[0122] Alternatively, the reflection reduction unit 81 may include flocked paper. For example, the flocked paper may be composed of a base material such as paper or cloth and chemical fibers attached upright to the base material. If black flocked paper is used, it is possible to further reduce the reflection of unwanted light compared to flocked paper of other colors.

[0123] In such lighting device 1B, for example, unwanted light obtained when fluorescence L1 is reflected and scattered by optical system 6 travels toward reflection reduction portion 81 on the inner wall of cylindrical portion 73 and is incident on reflection reduction portion 81. Since reflection reduction portion 81 reduces the reflection of unwanted light, it is possible to reduce the unwanted light that is emitted from emission opening 7a. Therefore, lighting device 1B can emit high-quality fluorescence L1 with even less unevenness into illumination space S1.

[0124] Fig. 14 is an enlarged view schematically illustrating a portion of another example of the light reducing structure 8. The light reducing structure 8 includes an uneven shape 82. The uneven shape 82 is, for example, the shape of the inner wall surface of the cylindrical portion 73, and Fig. 14 illustrates a portion of the uneven shape 82. The uneven shape 82 exhibits unevenness in the optical axis direction parallel to the optical axis AX1. In other words, the uneven shape 82 has a shape in which concave and convex portions are alternately arranged in a cross section including the optical axis AX1.

[0125] 14 , the uneven shape 82 has a sawtooth shape, and each tooth of the sawtooth (i.e., a convex portion) is formed by a first surface 821 on the wavelength conversion member 4 side and a second surface 822 on the emission opening 7a side. In the uneven shape 82, the first surfaces 821 and the second surfaces 822 are alternately arranged. Such an uneven shape 82 may have a spiral shape similar to a female screw, or may have a shape in which multiple ring shapes are arranged in the optical axis direction. The pitch of the uneven shape 82 is set to, for example, approximately several mm or less.

[0126] 14 , the length of the second surface 822 that moves away from the optical axis AX1 toward the exit opening 7a may be longer than that of the first surface 821. Furthermore, the angle that the second surface 822 forms with respect to the optical axis AX1 may be smaller than the angle that the first surface 821 forms with respect to the optical axis AX1. In the example of FIG. 12 , the first surface 821 is substantially perpendicular to the optical axis AX1, and therefore, in a cross section including the optical axis AX1, the first surface 821 corresponds to the adjacent side of a right triangle and corresponds to the hypotenuse of the right triangle of the second surface 822.

[0127] Unwanted light is incident on the inner wall surface of such cylindrical portion 73 mainly in an oblique direction from the wavelength conversion member 4 side. The first surface 821 reflects and scatters the incident unwanted light mainly toward the opposite side from the emission opening 7a. In other words, the first surface 821 reflects and scatters the unwanted light mainly in an oblique direction toward the wavelength conversion member 4 side. Although some of the unwanted light from the first surface 821 may be incident on the second surface 822, the second surface 822 is inclined, so that most of the unwanted light can be reflected and scattered in an oblique direction toward the wavelength conversion member 4 side.

[0128] Furthermore, even if unwanted light from the wavelength conversion member 4 side is incident on the second surface 822, the unwanted light reflected and scattered by the second surface 822 is incident on the first surface 821, and is reflected and scattered by the first surface 821 in an oblique direction toward the wavelength conversion member 4 side.

[0129] As described above, unwanted light incident on the uneven shape 82 from the wavelength conversion member 4 side can be mainly reflected and scattered in an oblique direction toward the wavelength conversion member 4 side. This increases the number of times the unwanted light is reflected and scattered within the housing 7, and allows the unwanted light to be attenuated within the housing 7. Therefore, it is possible to reduce the possibility that unwanted light will be emitted from the exit opening 7a.

[0130] FIG. 15 is a diagram schematically illustrating another example of the configuration of the lighting device 1 according to the third embodiment. Hereinafter, the lighting device 1 in FIG. 15 will be referred to as lighting device 1C. The lighting device 1C differs from the lighting device 1A in the presence or absence of a light-reducing structure 8. The light-reducing structure 8 is located on at least a portion of the inner wall of the housing 7. More specifically, the light-reducing structure 8 is located on at least a portion of the inner wall of the housing 71. In the example of FIG. 15 , the housing 71 includes a cylindrical portion 711 that houses the lenses 61A and 61B, a connecting portion 712 that houses the wavelength separation filter 5, and a cylindrical portion 713 that houses the lens 61C. An exit opening 7a is formed at the end of the cylindrical portion 713 opposite the connecting portion 712.

[0131] In the example of FIG. 15 , the light reducing structure 8 is located on at least a portion of the inner walls of the cylindrical portion 711 and the cylindrical portion 713. In the example of FIG. 15 , the light reducing structure 8 is located on the inner wall of the cylindrical portion 711 between the lens 61B and the wavelength separation filter 5, on the inner wall of the cylindrical portion 713 between the wavelength separation filter 5 and the lens 61C, and between the lens 61C and the emission opening 7a. As shown in FIG. 15 , the light reducing structure 8 does not have to be located between the lens 61A and the lens 61B on the inner wall of the cylindrical portion 711. The light reducing structure 8 may be formed on the entire periphery of the inner walls of the cylindrical portion 711 and the cylindrical portion 713. A reflection reduction portion 81 or an uneven shape 82 may be applied to the light reducing structure 8.

[0132] In the lighting device 1C, as in the lighting device 1B, the possibility of unwanted light being emitted from the emission opening 7a can be reduced.

[0133] 4. Fourth Embodiment An example of the configuration of the illumination device 1 according to the fourth embodiment is similar to that of the illumination device 1 according to any one of the first to third embodiments. In the fourth embodiment, an angle for defining the numerical aperture of the optical system 6 will be described. FIG. 16 is an enlarged view of a portion of the configuration of the illumination device 1. In the example of FIG. 16, an opening 70 is located between the wavelength conversion member 4 and the optical system 6 in the path of the fluorescence L1. The opening 70 has a second opening (hereinafter referred to as the diaphragm aperture) 7b. Light of the fluorescence L1 from the wavelength conversion member 4 having a divergence angle φ1 or less passes through the diaphragm aperture 7b and enters the optical system 6 (specifically, the lens 61A). In other words, the diaphragm aperture 7b of the opening 70 allows light of the fluorescence L1 having a divergence angle φ1 or less to pass toward the optical system 6. Conversely, light of the fluorescence L1 traveling at a divergence angle greater than the divergence angle φ1 (hereinafter referred to as the blocked light) is blocked by the opening 70. The opening 70 may be part of the housing 7.

[0134] The area of ​​the surface of the wavelength conversion member 4 as viewed along the optical axis direction parallel to the optical axis AX1 may be smaller than the minimum value of the opening area of ​​the diaphragm aperture 7b of the opening 70. This allows a larger portion of the fluorescence L1 that spreads and travels from the wavelength conversion member 4 to pass through the diaphragm aperture 7b.

[0135] As shown in FIG. 16 , in the illumination device 1, the angle ψ1 defining the numerical aperture of the optical system 6 may be equal to or greater than the divergence angle φ1 of the fluorescence L1 passing through the aperture 7b. The numerical aperture is the product of the sine of half the value of the angle ψ1 and the refractive index. The angle ψ1 is, for example, the angle formed by the outermost rays of virtual light that can pass through the effective area of ​​the optical system 6. The effective area here corresponds to the area through which light passes through which the optical performance of the optical system 6 can be exhibited. For example, the effective area of ​​the lens 61A is the area of ​​the lens 61A excluding a predetermined peripheral width. As a more specific example, the effective area of ​​the lens 61A may be the area surrounded by the inner peripheral edge of a portion of the housing 7 (e.g., a lens holder) that holds the peripheral edge of the lens 61A. In the example of FIG. 16 , the divergence angle φ1 and the angle ψ1 are equal to each other.

[0136] If the divergence angle φ1 is equal to or smaller than the angle ψ1, the fluorescence L1 passing through the diaphragm aperture 7b can pass through the effective area of ​​the optical system 6. Therefore, almost no fluorescence L1 is incident on the edges of the lenses 61A to 61C of the optical system 6, reducing or avoiding unnecessary reflection and scattering of the fluorescence L1 at the edges. This allows the illumination device 1 to emit high-quality fluorescence L1 with even less glare into the illumination space S1.

[0137] As described above, the lighting devices 1, 1A to 1C have been described in detail. However, the above description is merely an example in all respects, and the lighting devices 1, 1A to 1C are not limited thereto. It is understood that countless variations not illustrated can be envisioned without departing from the scope of this disclosure. The configurations described in the above embodiments and variations (or aspects) can be combined or omitted as appropriate, as long as they are not mutually inconsistent.

[0138] It goes without saying that all or part of the components constituting each of the above-described embodiments and various modified examples (or each aspect) can be combined as appropriate within the scope of not causing any contradiction.

[0139] For example, lenses such as lens 61A and lens 61B do not have to be located between the wavelength conversion member 4 and the wavelength separation filter 5. Alternatively, an aspherical lens 31 may be located between the wavelength conversion member 4 and the wavelength separation filter 5. In this case, the fluorescence L1 from the wavelength conversion member 4 passes through the aspherical lens 31 and enters the wavelength separation filter 5. Furthermore, the wavelength separation filter 5 does not necessarily have to be a dichroic mirror. For example, the wavelength separation filter 5 may be a dichroic prism.

[0140] This disclosure includes the following:

[0141] In one embodiment, (1) an illumination device may be an illumination device that emits illumination light into an external illumination space, and may include: a housing having a first opening that opens into the illumination space; a light source that emits excitation light into the housing; an aspherical lens located inside the housing, into which the excitation light from the light source is incident and that flattens the intensity distribution of the excitation light; a wavelength conversion member located inside the housing, into which the excitation light from the aspherical lens is incident and that emits fluorescence as the illumination light having a spectrum different from that of the excitation light, based on the excitation light; and a wavelength separation filter located inside the housing, that guides the excitation light from the aspherical lens to the wavelength conversion member and guides the fluorescence from the wavelength conversion member to the first opening.

[0142] (2) In the lighting device of (1) above, the aspherical surface of the aspherical lens may have a concave shape, and the curvature of a first central portion of the aspherical surface on the central side may be greater than the curvature of a first non-central portion of the aspherical surface located outside the first central portion.

[0143] (3) In the illumination device of (2) above, the surface of the aspherical lens opposite to the aspherical surface may have a convex shape.

[0144] (4) In the lighting device of (3) above, the curvature of a second central portion of the opposite surface of the aspherical lens may be greater than the curvature of a second non-central portion of the opposite surface that is located outside the second central portion.

[0145] (5) In the lighting device of (1) above, the aspherical surface of the aspherical lens may have a convex shape, and the curvature of a first central portion of the aspherical surface may be smaller than the curvature of a first non-central portion of the aspherical surface that is located outside the first central portion.

[0146] (6) In the illumination device of (1) above, the aspherical surface of the aspherical lens may have a convex shape, and the curvature of a first central portion of the aspherical surface may be greater than the curvature of a first non-central portion of the aspherical surface that is located outside the first central portion, and the excitation light from the aspherical lens may have a portion that is condensed between the aspherical lens and the wavelength conversion member.

[0147] (7) In any one of the illumination devices (2) to (6) above, of the excitation light emitted by the light source, central light having an intensity of 50% or more of the peak intensity can be incident on the first central portion of the aspherical lens, and peripheral light on the outer periphery side of the central light can be incident on the first non-central portion of the aspherical lens.

[0148] (8) In any one of the illumination devices (1) to (7) above, a graph showing the relationship between the second derivative of the angle formed by the surface normal at a position within the aspherical surface of the aspherical lens and the optical axis of the aspherical lens with respect to the distance between the optical axis and the position and the distance can have a minimum value.

[0149] (9) In the illumination device of (8) above, the graph may have the minimum value at least in a region of 30% or less of the effective diameter of the aspherical lens.

[0150] (10) In the illumination device according to any one of (1) to (9) above, the aspherical lens may have a conic coefficient indicating the shape of the aspherical surface of the aspherical lens that is not less than −60 and not more than −3.

[0151] (11) In the illumination device according to any one of (1) to (10) above, in the intensity distribution of the excitation light in the wavelength conversion member, a ratio of a first width of a region having an intensity of 50% or more of the peak intensity to a second width of a region having an intensity of 90% or more of the peak intensity may be 0.7 or more.

[0152] (12) Any one of the illumination devices (1) to (11) above may further include a cylindrical lens positioned between the light source and the wavelength separation filter, which adjusts the aspect ratio of the cross-sectional shape of the excitation light.

[0153] (13) In the lighting device of (12) above, the cylindrical lens can be positioned between the light source and the aspherical lens.

[0154] (14) The illumination device of (12) or (13) above may further include a holder that holds the cylindrical lens and the aspherical lens together.

[0155] (15) In the lighting device according to any one of (1) to (14) above, the peak wavelength of the excitation light may be 415 nm or less, and the wavelength conversion member may contain a plurality of types of phosphors.

[0156] (16) In the lighting device according to any one of (1) to (15) above, the light source may include a semiconductor laser element.

[0157] (17) In any one of the lighting devices (1) to (16) above, a light reducing structure may be located on the inner wall of the housing to absorb unnecessary light generated by reflection or scattering of the fluorescence, or to reflect or scatter the unnecessary light toward the wavelength conversion member.

[0158] (18) Any one of the illumination devices described in (1) to (17) above may include an optical system that is located on a path of the fluorescence from the wavelength conversion member to the first opening and that focuses the fluorescence on a virtual image plane on the first opening side.

[0159] (19) The illumination device of (18) above may further include an opening having a second opening that allows the fluorescence from the wavelength conversion member, the fluorescence having a predetermined divergence angle or less, to pass toward the optical system and blocks the fluorescence having a larger divergence angle than the predetermined divergence angle, and the angle that defines the numerical aperture of the optical system may be equal to or larger than the predetermined divergence angle.

[0160] (20) In the illumination device of (18) or (19) above, the optical system includes a plurality of lenses positioned on the path.

[0161] REFERENCE SIGNS LIST 1, 1A to 1C Illumination device 2 Light source 31 Aspherical lens 31a Aspherical surface 31aa First central portion 31ab First non-central portion 31b Opposite surface 31ba Second central portion 31bb Second non-central portion 32 Cylindrical lens 4 Wavelength conversion member 5 Wavelength separation filter 6 Optical system 7 Housing 70 Opening 721 Holder 7a First opening (exit opening) 7b Second opening (aperture opening) 8 Light reduction structure BW1 Part (light collecting portion) D1 First width D2 Second width L0 Excitation light L0a Central light L0b Peripheral light

Claims

1. A lighting device that emits illumination light into an external illumination space, a housing having a first opening that opens into the illumination space; A light source that emits excitation light into the housing; an aspheric lens located inside the housing, into which the excitation light from the light source is incident and which flattens the intensity distribution of the excitation light; a wavelength conversion member located inside the housing, receiving the excitation light from the aspherical lens and emitting fluorescence as the illumination light having a spectrum different from that of the excitation light based on the excitation light; a wavelength separation filter located inside the housing, which guides the excitation light from the aspherical lens to the wavelength conversion member and guides the fluorescence from the wavelength conversion member to the first opening; A lighting device comprising:

2. 2. The lighting device according to claim 1, the aspheric surface of the aspheric lens has a concave shape; an illumination device, wherein a curvature of a first central portion of the aspheric surface on a central side is greater than a curvature of a first non-central portion of the aspheric surface located outside the first central portion.

3. 3. The lighting device according to claim 2, An illumination device, wherein a surface of the aspherical lens opposite to the aspherical surface has a convex shape.

4. 4. The lighting device according to claim 3, an illumination device, wherein a curvature of a second central portion of the opposite surface of the aspheric lens is greater than a curvature of a second non-central portion of the opposite surface that is located outside the second central portion.

5. 2. The lighting device according to claim 1, the aspheric surface of the aspheric lens has a convex shape; an illumination device, wherein a curvature of a first central portion of the aspheric surface is smaller than a curvature of a first non-central portion of the aspheric surface that is located outside the first central portion.

6. 2. The lighting device according to claim 1, the aspheric surface of the aspheric lens has a convex shape; a curvature of a first central portion of the aspheric surface is greater than a curvature of a first non-central portion of the aspheric surface that is located outside the first central portion; an illumination device, wherein the excitation light from the aspherical lens has a portion where the light is condensed between the aspherical lens and the wavelength conversion member;

7. 7. The lighting device according to claim 2, an illumination device, wherein, of the excitation light emitted by the light source, central light having an intensity of 50% or more of a peak intensity is incident on the first central portion of the aspherical lens, and peripheral light that is more outer than the central light is incident on the first non-central portion of the aspherical lens.

8. 7. The lighting device according to claim 1, An illumination device, wherein a graph showing the relationship between a second derivative of an angle between a surface normal at a position within the aspherical surface of the aspherical lens and an optical axis of the aspherical lens with respect to a distance between the optical axis and the position and the distance has a minimum value.

9. 9. The lighting device according to claim 8, The graph shows that, at least in a region of 30% or less of the effective diameter of the aspherical lens, A lighting device having said minimum value.

10. 7. The lighting device according to claim 1, An illumination device, wherein a Conic coefficient indicating the aspheric shape of the aspheric lens is greater than or equal to -60 and less than or equal to -3.

11. 7. The lighting device according to claim 1, a ratio of a first width of a region having an intensity of 50% or more of a peak intensity to a second width of a region having an intensity of 90% or more of the peak intensity in an intensity distribution of the excitation light in the wavelength conversion member is 0.7 or more.

12. 7. The lighting device according to claim 1, The illumination device further comprises a cylindrical lens positioned between the light source and the wavelength separation filter, the cylindrical lens adjusting an aspect ratio of a cross-sectional shape of the excitation light.

13. 13. The lighting device according to claim 12, The illumination device, wherein the cylindrical lens is located between the light source and the aspherical lens.

14. 13. The lighting device according to claim 12, The illumination device further comprises a holder that holds the cylindrical lens and the aspherical lens together.

15. 7. The lighting device according to claim 1, The peak wavelength of the excitation light is 415 nm or less, The illumination device, wherein the wavelength conversion member includes a plurality of types of phosphors.

16. 7. The lighting device according to claim 1, The light source includes a semiconductor laser element.

17. 7. The lighting device according to claim 1, the lighting device, wherein a light reducing structure is located on an inner wall of the housing, and the light reducing structure absorbs unnecessary light generated by reflection or scattering of the fluorescence, or reflects or scatters the unnecessary light toward the wavelength conversion member.

18. 7. The lighting device according to claim 1, an optical system that is located on a path of the fluorescence from the wavelength conversion member to the first opening and that forms an image of the fluorescence on a virtual image plane on a side of the first opening.

19. 20. The lighting device according to claim 18, an opening portion having a second opening that passes the fluorescence having a predetermined spread angle or less to the optical system side among the fluorescence from the wavelength conversion member and blocks the fluorescence having a spread angle larger than the predetermined spread angle, An illumination device, wherein an angle defining a numerical aperture of the optical system is equal to or greater than the predetermined divergence angle.

20. 20. The lighting device according to claim 18, The optical system of the illumination device includes a plurality of lenses positioned on the path.