Lighting device and color conversion element

Abstract

A lighting device (100) comprises: a white light source (110) that includes a blue light-emitting element and a yellow phosphor and emits first white light; and a color conversion element (130) that converts the first white light into second white light. Where the average transmittance in the range of 435-480 nm of the color conversion element (130) is defined as TB, the average transmittance in the range of 540-590 nm of the color conversion element (130) is defined as TG, the color temperature (unit: K) of the first white light is defined as T1, and the color temperature (unit: K) of the second white light is defined as T2, 2500 ≤ (TG / TB) * T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied.

Description

Illumination device and color conversion element

[0001] The present invention relates to a lighting device and a color conversion element.

[0002] Patent Document 1 discloses an optical filter including an optical multilayer film that selectively improves the average reflectance of light in the green to yellow wavelength range and the blue wavelength range. It is stated that the optical filter disclosed in Patent Document 1 can improve color rendering properties while suppressing a decrease in luminous efficiency and a change in color temperature.

[0003] Patent No. 6058948

[0004] An object of the present invention is to provide an illumination device and a color conversion element that can achieve both improved color rendering properties and a lower color temperature.

[0005] An illumination device according to one aspect of the present invention includes a white light source including a blue light-emitting element and a yellow phosphor, and emitting first white light; and a color conversion element that converts the first white light into second white light, wherein TB denotes an average transmittance of the color conversion element in a range of 435 nm to 480 nm, TG denotes an average transmittance of the color conversion element in a range of 540 nm to 590 nm, T1 denotes a color temperature (unit: K) of the first white light, and T2 denotes a color temperature (unit: K) of the second white light, and the following relationships are satisfied: 2500≦(TG÷TB)×T2≦5000, and T1−T2≧300.

[0006] A color conversion element according to one aspect of the present invention is a color conversion element that converts first white light into second white light, wherein TB denotes the average transmittance of the color conversion element in the range of 435 nm or more and 480 nm or less, TG denotes the average transmittance of the color conversion element in the range of 540 nm or more and 590 nm or less, T1 denotes the color temperature (unit: K) of the first white light, and T2 denotes the color temperature (unit: K) of the second white light, and the relationships 2500≦(TG÷TB)×T2≦5000 and T1−T2≧300 are satisfied.

[0007] According to the present invention, it is possible to achieve both improved color rendering properties and a lower color temperature.

[0008] FIG. 1 is a schematic perspective view of an illumination device according to an embodiment. FIG. 2 is a diagram illustrating the configuration of an illumination device according to an embodiment. FIG. 3 is a schematic plan view of a white light source of an illumination device according to an embodiment. FIG. 4 is a schematic cross-sectional view of a white light-emitting element of an illumination device according to an embodiment. FIG. 5 is a diagram illustrating the transmittance of a color conversion element according to a comparative example and the intensity of light before and after passing through the color conversion element. FIG. 6 is a diagram illustrating the transmittance of a color conversion element according to Example 1 and the intensity of light before and after passing through the color conversion element. FIG. 7 is a diagram illustrating the transmittance of a color conversion element according to Example 2 and the intensity of light before and after passing through the color conversion element. FIG. 8 is a diagram illustrating the transmittance of a color conversion element according to Example 3 and the intensity of light before and after passing through the color conversion element. FIG. 9 is a diagram illustrating the transmittance of a color conversion element according to Example 4 and the intensity of light before and after passing through the color conversion element. FIG. 10 is a diagram illustrating the transmittance of a color conversion element according to Example 5 and the intensity of light before and after passing through the color conversion element. FIG. 11 is a diagram illustrating the transmittance of a color conversion element according to Example 6 and the intensity of light before and after passing through the color conversion element. Fig. 12 is a diagram showing the transmittance of a prototype of the color conversion element shown in Fig. 7 and the intensity of light before and after passing through the prototype. Fig. 13 is a diagram showing the transmittance of a prototype of the color conversion element shown in Fig. 10 and the intensity of light before and after passing through the prototype. Fig. 14 is a diagram showing the transmittance of a prototype of the color conversion element shown in Fig. 11 and the intensity of light before and after passing through the prototype. Fig. 15 is a diagram showing the relationship between the color temperature of transmitted light through a color conversion element and an evaluation index.

[0009] The following describes in detail lighting devices and color conversion elements according to embodiments of the present invention with reference to the drawings. Each of the embodiments described below represents a specific example of the present invention. Therefore, the numerical values, shapes, materials, components, component arrangements and connection forms, steps, and step sequences shown in the following embodiments are merely examples and are not intended to limit the present invention. Therefore, among the components in the following embodiments, components not recited in the independent claims are described as optional components.

[0010] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0011] Furthermore, in this specification, terms indicating relationships between elements such as parallelism, terms indicating the shapes of elements, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0012] For example, in this specification, "parallel light" does not mean only completely parallel light, but also means so-called approximately parallel light, that is, light that can be considered to be substantially parallel light and that can expand or converge within a few percent.

[0013] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0014] (Embodiment) [Configuration] First, the configuration of a lighting device according to an embodiment will be described with reference to FIGS. 1 to 4. FIG.

[0015] Fig. 1 is a schematic perspective view of an illumination device 100 according to the present embodiment. Fig. 2 is a diagram showing the configuration of the illumination device 100 according to the present embodiment. Fig. 3 is a schematic plan view of a white light source 110 of the illumination device 100 according to the present embodiment. Fig. 4 is a schematic cross-sectional view of a white light-emitting element 111 of the illumination device 100 according to the present embodiment. Note that in Fig. 4, the hatching representing the cross section is omitted.

[0016] 1, the lighting device 100 is, for example, a spotlight, and is attached to a wiring fixture (for example, a wiring duct or a ceiling hook) provided on a ceiling or wall. The lighting device 100 may also be a downlight or a ceiling light.

[0017] 2, the lighting device 100 includes a white light source 110, a first optical system 120, a color conversion element 130, and a second optical system 140. Furthermore, as shown in FIG. 1, the lighting device 100 includes a housing 150.

[0018] The white light source 110 is a light source that emits white light L11. The white light L11 is an example of first white light. As shown in FIG. 3 , the white light source 110 includes a plurality of white light-emitting elements 111 arranged in a two-dimensional matrix. The plurality of white light-emitting elements 111 are regularly arranged in a matrix of M rows and N columns. Here, M and N are natural numbers of 2 or greater. M=N may be satisfied, or M≠N may be satisfied. The arrangement intervals of the white light-emitting elements 111 in the row direction and the column direction may be the same or different. The outer shape of the area in which the plurality of white light-emitting elements 111 are arranged is rectangular, but may also be circular.

[0019] The plurality of white light emitting elements 111 have the same configuration. Specifically, as shown in Fig. 4, the white light emitting elements 111 include blue light emitting elements 112 and yellow phosphor 114. Yellow phosphor 114 is disposed on the light emitting side of blue light emitting element 112.

[0020] The blue light emitting element 112 emits blue light Lb. The blue light emitting element 112 is, for example, an LED (Light Emitting Diode). The blue light emitting element 112 is, for example, a minute LED having a size of 100 μm×100 μm or less, but is not limited to this. The blue light emitting element 112 may also be a blue semiconductor laser element.

[0021] Yellow phosphor 114 is a phosphor that is excited by blue light Lb and emits yellow light Ly. A mixture of yellow light Ly and blue light Lb that has passed through yellow phosphor 114 is white light L11 emitted from white light-emitting element 111. Yellow phosphor 114 is, for example, a YAG (yttrium aluminum garnet)-based phosphor, but is not limited to this. Yellow phosphor 114 is provided in contact with the light-emitting surface of blue light-emitting element 112.

[0022] Note that blue light emitting elements 112 and yellow phosphor 114 may be arranged apart from each other. Furthermore, blue light emitting elements 112 and yellow phosphor 114 do not have to be arranged in a one-to-one relationship. Furthermore, yellow phosphor 114 may be arranged so as to cover a plurality of blue light emitting elements 112. For example, for a plurality of blue light emitting elements 112 arranged in a two-dimensional matrix, a yellow fluorescent plate that entirely covers the plurality of blue light emitting elements 112 may be arranged as yellow phosphor 114.

[0023] Although not shown in the figure, the lighting device 100 includes a control unit that controls the light emission of the multiple white light-emitting elements 111 (blue light-emitting elements 112). The control unit independently controls each of the multiple blue light-emitting elements 112. That is, the control unit can individually control the on / off, light emission intensity, light emission time, etc. of each of the multiple blue light-emitting elements 112. For example, by individually controlling the on / off of the multiple blue light-emitting elements 112, it is possible to emit illumination light with different brightness levels in each region.

[0024] The control unit is realized, for example, by an LSI (Large Scale Integration), which is an integrated circuit (IC). The integrated circuit is not limited to an LSI, but may be a dedicated circuit or a general-purpose processor. For example, the control unit may be a microcontroller. The microcontroller includes, for example, a non-volatile memory in which a program is stored, a volatile memory that is a temporary storage area for executing the program, input / output ports, and a processor that executes the program. Furthermore, the control unit may be a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor that allows the connections and settings of circuit cells within the LSI to be reconfigured. The functions performed by the control unit may be realized by software or hardware.

[0025] The first optical system 120 converts the white light L11 emitted from the white light source 110 into parallel light. As shown in Fig. 2, the first optical system 120 converts the white light L11 into parallel white light L12 and emits the parallel white light L12 toward the color conversion element 130. The first optical system 120 is, for example, a single collimator lens, but is not limited to this. The first optical system 120 may be realized by multiple collimator lenses, or may include other optical elements such as mirrors and / or condenser lenses.

[0026] In this embodiment, as shown in FIG. 2 , the first optical system 120 is disposed between the white light source 110 and the color conversion element 130. The first optical system 120 is disposed so as to cover the entire light emission surface of the white light source 110, and converts the white light L11 from each of the plurality of white light emitting elements 111 into parallel white light L12. Note that the first optical system 120 only needs to be optically disposed between the white light source 110 and the color conversion element 130. In other words, the first optical system 120 only needs to be disposed on the optical path of the first white light from the white light source 110 to the color conversion element 130. At least a portion of the first optical system 120 does not need to be physically (mechanically) disposed between the white light source 110 and the color conversion element 130.

[0027] The color conversion element 130 is an element that converts the first white light into a second white light. The second white light is light having a different color temperature from the first white light. Specifically, the color conversion element 130 suppresses transmission of specific wavelength components of the first white light, thereby emitting the second white light having a different color temperature and spectrum from the first white light.

[0028] In this embodiment, as shown in Fig. 2, the color conversion element 130 converts the white light L12 into the white light L21. The white light L12 is an example of the first white light emitted from the white light source 110, and has a spectrum substantially equivalent to that of the white light L11. That is, the white light L12 and the white light L11 have substantially the same color temperature. The white light L21 is an example of the second white light, and has a spectrum and color temperature different from those of the white light L12. The specific transmission spectrum of the color conversion element 130 will be described later.

[0029] In this embodiment, the color conversion element 130 is an optical element that adjusts the spectral transmittance by utilizing the reflection of light. For example, the color conversion element 130 is a dichroic filter. The dichroic filter has a multilayer structure in which dielectric films with high refractive indexes and dielectric films with low refractive indexes are alternately stacked. The dielectric films are made of SiO ２ , TiO ２ , Nb ２ O ５ , HfO ２ It is possible to use metal oxide films such as: By adjusting the materials of the two types of dielectric films, the thickness of each film, the number of layers, etc., it is possible to realize a desired transmission spectrum.

[0030] The second optical system 140 projects the white light L21 emitted from the color conversion element 130. As shown in Fig. 2, the second optical system 140 converts the white light L21 into white light L22, which is projection light, and emits the white light L22 to the outside. The second optical system 140 is, for example, but is not limited to, one or more projection lenses. The second optical system 140 may include other optical elements such as a mirror and / or a condenser lens.

[0031] The housing 150 accommodates the white light source 110, the first optical system 120, the color conversion element 130, and the second optical system 140. The housing 150 includes, for example, but is not limited to, an outer housing that forms the outer shell of the lighting device 100 and a plurality of components such as a heat sink. The components that make up the housing 150 are formed using resin or metal.

[0032] An opening is provided in the housing 150 on the light emission side of the white light source 110 (in the normal direction of the main surface of the substrate), and the second optical system 140 is arranged to close the opening. For example, if the light emission of the plurality of blue light emitting elements 112 can be controlled individually, there is no need to provide a liquid crystal device or a DMD (Digital Mirror Device) inside the housing 150, as is the case with a general projector, and therefore the illumination device 100 can be made smaller.

[0033] [Color Conversion Element] Next, a specific transmission spectrum of the color conversion element 130 will be described.

[0034] The color conversion element 130 has high transmittance for light in the visible light band except for two wavelength bands. That is, the transmission spectrum of the color conversion element 130 has two transmittance valleys, i.e., wavelength bands where the transmittance is lower than a predetermined value. The predetermined value is, for example, 60%. In this specification, the visible light band is considered to be the range from 400 nm to 750 nm.

[0035] Specifically, the color conversion element 130 is designed to have low transmittance for blue components with wavelengths of 450 nm or less and green components with wavelengths around 550 nm. For example, the minimum transmittance of the color conversion element 130 in the range of 400 nm to 450 nm is smaller than the minimum transmittance of the color conversion element 130 in the range of 525 nm to 575 nm. The minimum transmittance of the color conversion element 130 in the range of 400 nm to 450 nm is, but is not limited to, 10% to 60%. The minimum transmittance of the color conversion element 130 in the range of 400 nm to 450 nm may be, but is not limited to, 50% or less, 40% or less, 30% or less, or 20% or less. Furthermore, the minimum transmittance of the color conversion element 130 in the range of 525 nm to 575 nm is, but is not limited to, 20% to 70%. The minimum transmittance of the color conversion element 130 in the range of 525 nm to 575 nm may be 60% or less, 50% or less, or 40% or less. The minimum transmittance of the color conversion element 130 in the range of 525 nm to 575 nm may be 30% or more.

[0036] Furthermore, for example, the maximum value of the transmittance of the color conversion element 130 in the range of 450 nm or more and 500 nm or less, and the maximum value of the transmittance of the color conversion element 130 in the range of 600 nm or more and 750 nm or less are 90% or more, but may also be 95% or more, or 97% or more.

[0037] The average transmittance of the color conversion element 130 in the range of 435 nm to 480 nm is defined as TB, and the average transmittance of the color conversion element 130 in the range of 540 nm to 590 nm is defined as TG. In this case, the following formula (1) is satisfied.

[0038] (1) 2500≦(TG ÷ TB) × T2≦5000

[0039] The average transmittance is the average value of the spectral transmittance (transmittance for each wavelength) in the corresponding range. By satisfying the above formula (1), the color rendering properties of the white light L21 emitted from the color conversion element 130 can be improved.

[0040] The average color rendering index Ra of the white light L12 before it enters the color conversion element 130 is approximately 70. Because the white light L12 is a mixture of blue light Lb from the blue light emitting element 112 and yellow light Ly from the yellow phosphor 114, the blue and yellow components are strong and the color rendering properties are low.

[0041] In contrast, the color conversion element 130 has a low transmittance for the blue and yellow components of the white light L12, so the transmission of blue and yellow light is suppressed. As a result, the white light L21 that has passed through the color conversion element 130 has a reduced intensity spectrum and resembles natural white light (sunlight). As a result, the general color rendering index Ra of the white light L21 that has passed through the color conversion element 130 can be made 90 or higher.

[0042] Furthermore, the transmittance of blue light is set lower than the transmittance of yellow light in the color conversion element 130. That is, the color conversion element 130 suppresses the transmission of blue light, so that the color temperature of the white light after transmission can be lowered.

[0043] Specifically, the color temperature of the white light L21 is lower than the color temperature of the white light L12. The color temperatures (unit: K) of the white lights L11 and L12 are T1, and the color temperature (unit: K) of the white light L21 is T2. In this case, the following formula (2) is satisfied.

[0044] (2) T1-T2≧300

[0045] For example, the color temperature T1 of the white light L12 is 5000 K or higher, or may be 5200 K or higher, 5500 K or higher, 5700 K or higher, or 6000 K or higher. The color temperature T2 of the white light L21 is lower than the color temperature T1 of such white light L12 by 300 K or more.

[0046] [Examples] Next, several specific examples of the color conversion element 130 will be described with reference to FIGS.

[0047] Fig. 5 is a diagram showing the transmittance of a color conversion element according to a comparative example and the intensity of light before and after passing through the color conversion element. Figs. 6 to 11 are diagrams showing the transmittance of color conversion elements according to examples 1 to 6 and the intensity of light before and after passing through the color conversion element.

[0048] Figures 5 to 11 show the results of simulations of the transmission spectra of color conversion elements whose spectral transmittances are designed to achieve target values ​​for the color temperature of white light passing through the color conversion element, while Figures 12 to 14 show the transmittances of prototypes (sample products) of the color conversion elements shown in Figures 7, 10, and 11, respectively, and the intensities of light before and after passing through the prototypes.

[0049] In each figure, the horizontal axis represents the wavelength of light, and the vertical axis represents the transmittance or light intensity. The transmittance is expressed as the ratio of the intensity of the emitted light to the intensity of the incident light. The light intensity is expressed in arbitrary units.

[0050] The spectrum of the first white light incident on the color conversion element is common to the comparative example and examples 1 to 6. The color temperature T1 of the first white light is 5500 K. For example, as shown in FIG. 5 , the first white light has a first intensity peak of a blue component and a second intensity peak of a yellow component. The peak wavelength of the first intensity peak is approximately 447 nm. Note that the peak wavelength is the wavelength at which the light intensity is maximized. The peak wavelength of the second intensity peak is approximately 555 nm. The maximum intensity value of the first intensity peak is greater than the maximum intensity value of the second intensity peak. Furthermore, the half width of the first intensity peak is narrower than the half width of the second intensity peak.

[0051] The target color temperature of the comparative example shown in Figure 5 is 5500K. In other words, the color conversion element according to the comparative example is designed to improve color rendering without changing the color temperature. The target color temperatures of Examples 1 to 6 shown in Figures 6 to 11 are 5000K, 4500K, 4000K, 3500K, 3000K, and 3000K, respectively.

[0052] Table 1 summarizes the color temperature T2 of the transmitted light (second white light), the average transmittance TG in the range of 540 nm or more and 590 nm or less, the average transmittance TB in the range of 435 nm or more and 480 nm or less, the index A (= TG ÷ TB × T2) of formula (1), and the index B (= T1 - T2) of formula (2) for the comparative example and examples 1 to 6.

[0053]

[0054] Example 1 The target value of the color temperature of the color conversion element according to Example 1 shown in Fig. 6 is 5000 K. Therefore, index B in Table 1 is 500 K, which satisfies the condition of formula (2).

[0055] Furthermore, in the transmission spectrum of the color conversion element according to Example 1, the transmittance is set to be constant at 38% in the wavelength range of 400 nm to 440 nm. The transmittance is also set to be constant at 52% in the wavelength range of 540 nm to 585 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 460 nm to 525 nm and the wavelength range of 610 nm to 750 nm. In the transmittance transition portion (the range in which the transmittance increases or decreases with a change in wavelength), the transmittance is set to change at a constant rate. As a result, in Example 1, the average transmittance TG is 52%, the average transmittance TB is 76%, and the index A in Table 1 is 3421K, satisfying the condition of formula (1).

[0056] Example 2 The target value of the color temperature of the color conversion element according to Example 2 shown in Fig. 7 is 4500 K. Therefore, index B in Table 1 is 1000 K, which satisfies the condition of formula (2).

[0057] Furthermore, in the transmission spectrum of the color conversion element according to Example 2, the transmittance is set to be constant at 23% in the wavelength range of 400 nm to 440 nm. The transmittance is also set to be constant at 53.5% in the wavelength range of 535 nm to 585 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 460 nm to 515 nm and the wavelength range of 606 nm to 750 nm. In the transmittance transition portion, the transmittance is set to change at a constant rate. As a result, in Example 2, the average transmittance TG is 54%, and the average transmittance TB is 71%, and index A in Table 1 is 3422K, satisfying the condition of formula (1).

[0058] Example 3 The target value of the color temperature of the color conversion element according to Example 3 shown in Fig. 8 is 4000 K. Therefore, index B in Table 1 is 1500 K, which satisfies the condition of formula (2).

[0059] Furthermore, in the transmission spectrum of the color conversion element according to Example 3, the transmittance is set to be constant at 21.5% in the wavelength range of 400 nm to 444 nm. The transmittance is also set to be constant at 48.1% in the wavelength range of 535 nm to 575 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 464 nm to 515 nm and the wavelength range of 596 nm to 750 nm. In the transmittance transition portion, the transmittance is set to change at a constant rate. As a result, in Example 3, the average transmittance TG is 53%, and the average transmittance TB is 64%, and the index A in Table 1 is 3312K, satisfying the condition of formula (1).

[0060] Example 4 The target value of the color temperature of the color conversion element according to Example 4 shown in Fig. 9 is 3500 K. Therefore, index B in Table 1 is 2000 K, which satisfies the condition of formula (2).

[0061] Furthermore, in the transmission spectrum of the color conversion element according to Example 4, the transmittance is set to be constant at 19.5% in the wavelength range of 400 nm to 451 nm. The transmittance is also set to be constant at 41.2% in the wavelength range of 531 nm to 574 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 471 nm to 511 nm and the wavelength range of 595 nm to 750 nm. In the transmittance transition portion, the transmittance is set to change at a constant rate. As a result, in Example 4, the average transmittance TG is 48%, and the average transmittance TB is 52%, and index A in Table 1 is 3230K, satisfying the condition of formula (1).

[0062] Example 5 The target value of the color temperature of the color conversion element according to Example 5 shown in Fig. 10 is 3000 K. Therefore, index B in Table 1 is 2500 K, which satisfies the condition of formula (2).

[0063] In addition, in the transmission spectrum of the color conversion element according to Example 5, the transmittance is set to be constant at 11.3% in the wavelength range of 400 nm to 455 nm. The transmittance is also set to be constant at 29.9% in the wavelength range of 520 nm to 550 nm. The transmittance is also set to be constant at 54.5% in the wavelength range of 590 nm to 595 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 485 nm to 490 nm and the wavelength range of 625 nm to 750 nm. In the transmittance transition portion, the transmittance is set to change at a constant rate. As a result, in Example 5, the average transmittance TG is 40%, the average transmittance TB is 31%, and the index A in Table 1 is 3871 K, satisfying the condition of formula (1).

[0064] Example 6 The target value of the color temperature of the color conversion element according to Example 6 shown in Fig. 11 is 3000 K. Therefore, index B in Table 1 is 2500 K, which satisfies the condition of formula (2).

[0065] Furthermore, in the transmission spectrum of the color conversion element according to Example 6, the transmittance is set to be constant at 14.8% in the wavelength range of 400 nm to 455 nm. The transmittance is also set to be constant at 28% in the wavelength range of 536 nm to 552 nm. The transmittance is also set to be constant at 95% in both the wavelength range of 485 nm to 496 nm and the wavelength range of 608 nm to 750 nm. The transmittance is set to change at a constant rate in the transmittance transition portion. As a result, in Example 6, the average transmittance TG is 45%, the average transmittance TB is 34%, and the index A in Table 1 is 3970 K, satisfying the condition of formula (1).

[0066] <Prototype> The inventors of the present application created prototypes for Examples 2, 5, and 6 of the six examples described above. The prototypes were dichroic filters, and were adapted to the transmission characteristics shown in each example by adjusting the materials of the two types of dielectric films, the thickness of each film, the number of layers, etc.

[0067] 12 to 14, the transmission spectrum of each prototype has a gentler shape than the design value, but generally follows the transmission spectrum of the corresponding example. Parameters such as the color temperature T2 of the prototype are as shown in Table 2 below. The color temperature T1 of the first white light, which is the incident light, is 5534K.

[0068]

[0069] 15 is a diagram showing the relationship between the color temperature of transmitted light of a color conversion element and the evaluation index, in which the horizontal axis represents the color temperature of transmitted light and the vertical axis represents index A.

[0070] 15 plots the index A for a total of 19 examples, including 16 examples including Examples 1 to 6 described above and three prototypes. Note that because the color temperature T2 of the transmitted light (second white light) also depends on the color temperature and spectrum of the incident light (first white light), the index A is calculated for each of three different types of incident light. The three different types of incident light have color temperatures T1 of 5534 K, 5263 K, and 5684 K, respectively, and have spectra equivalent to the light intensity spectra before transmission shown in FIGS. 5 to 14.

[0071] 15, although there is some variation depending on the color temperature and spectral difference of the incident light, it can be seen that index A falls within the range of 2500 K or more and 5000 K or less, regardless of the color temperature of the transmitted light. In other words, it can be seen that by satisfying the relationship between the above formulas (1) and (2), it is possible to achieve both improved color rendering properties and a lower color temperature.

[0072] [Summary] As described above, an illumination device according to a first aspect of the present invention is, for example, the illumination device 100 described above, and includes a white light source 110 that includes a blue light-emitting element 112 and a yellow phosphor 114 and emits first white light, and a color conversion element 130 that converts the first white light into second white light. When the average transmittance of the color conversion element 130 in the range of 435 nm to 480 nm is denoted by TB, the average transmittance of the color conversion element 130 in the range of 540 nm to 590 nm is denoted by TG, the color temperature (unit: K) of the first white light is denoted by T1, and the color temperature (unit: K) of the second white light is denoted by T2, the relationships 2500≦(TG÷TB)×T2≦5000 and T1−T2≧300 are satisfied.

[0073] This allows for both improved color rendering and a lower color temperature. The white light L11 emitted from the white light source 110, which includes the blue light-emitting element 112 and the yellow phosphor 114, tends to have a higher color temperature due to the stronger blue component, making it difficult to achieve a lighting device with a low color temperature. By contrast, by utilizing the color conversion element 130, it is possible to lower the color temperature of white light with a high color temperature while improving color rendering.

[0074] Furthermore, the lighting device according to the second aspect of the present invention is the lighting device according to the first aspect, and includes a first optical system 120 that is arranged between the white light source 110 and the color conversion element 130 and converts the first white light emitted from the white light source 110 into parallel light.

[0075] This allows white light L12 to be incident on the color conversion element 130 from the front. Since the influence of the angle dependency of the transmittance of the color conversion element 130 can be suppressed, it is possible to achieve the desired high color rendering properties and low color temperature.

[0076] An illumination device according to a third aspect of the present invention is the illumination device according to the first or second aspect, and further includes a second optical system 140 that projects the second white light emitted from the color conversion element 130.

[0077] This allows white light with high color rendering properties and a low color temperature to be efficiently emitted to a desired area.

[0078] An illumination device according to a fourth aspect of the present invention is the illumination device according to any one of the first to third aspects, in which white light source 110 includes a plurality of blue light-emitting elements 112 arranged in a two-dimensional matrix, and yellow phosphor 114 is disposed on the light-emitting side of the plurality of blue light-emitting elements 112.

[0079] In this way, by arranging a plurality of blue light emitting elements 112 together in a small area, it is possible to increase the intensity while reducing the size of white light source 110. Reducing the size of white light source 110 can also contribute to reducing the size of the lighting device according to this embodiment.

[0080] An illumination device according to a fifth aspect of the present invention is the illumination device according to any one of the first to fourth aspects, wherein the blue light emitting element 112 is a blue semiconductor laser element.

[0081] This can improve energy efficiency.

[0082] An illumination device according to a sixth aspect of the present invention is the illumination device according to any one of the first to fifth aspects, wherein the color conversion element 130 is a dichroic filter.

[0083] This makes it possible to easily realize a color conversion element 130 having a desired transmission spectrum by adjusting the material, thickness, number of layers, etc. of the dielectric films that make up the dichroic filter.

[0084] Furthermore, an illumination device according to a seventh aspect of the present invention is an illumination device according to any one of the first to sixth aspects, in which the minimum transmittance value of the color conversion element 130 in the range of 400 nm or more and 450 nm or less is smaller than the minimum transmittance value of the color conversion element 130 in the range of 525 nm or more and 575 nm or less.

[0085] This makes it possible to suppress the transmission of yellow and blue components, thereby achieving both improved color rendering properties and a lower color temperature.

[0086] An illumination device according to an eighth aspect of the present invention is an illumination device according to any one of the first to seventh aspects, wherein the maximum value of the transmittance of the color conversion element 130 in the range of 450 nm or more and 500 nm or less, and the maximum value of the transmittance of the color conversion element 130 in the range of 600 nm or more and 750 nm or less, are 90% or more.

[0087] This can increase the light extraction efficiency.

[0088] Furthermore, a color conversion element according to a ninth aspect of the present invention is, for example, the above-described color conversion element 130, which is a color conversion element that converts first white light into second white light. When the average transmittance of the color conversion element in the range of 435 nm to 480 nm is denoted by TB, the average transmittance of the color conversion element in the range of 540 nm to 590 nm is denoted by TG, the color temperature (unit: K) of the first white light is denoted by T1, and the color temperature (unit: K) of the second white light is denoted by T2, the relationships 2500≦(TG÷TB)×T2≦5000 and T1−T2≧300 are satisfied.

[0089] This allows for both improved color rendering and a lower color temperature. The white light L11 emitted from the white light source 110, which includes the blue light-emitting element 112 and the yellow phosphor 114, tends to have a higher color temperature due to the stronger blue component, making it difficult to achieve a lighting device with a low color temperature. By contrast, by utilizing the color conversion element 130, it is possible to lower the color temperature of white light with a high color temperature while improving color rendering.

[0090] (Others) Although the lighting device according to the present invention has been described above based on the above embodiment, the present invention is not limited to the above embodiment.

[0091] For example, in the above embodiment, the white light source 110 includes a plurality of white light-emitting elements 111 arranged in a two-dimensional matrix, but is not limited to this. The white light source 110 may also be a single white light-emitting element.

[0092] The color conversion element 130 may be an optical element that adjusts the spectral transmittance by utilizing light absorption. For example, the color conversion element 130 may include a light-transmitting substrate made of resin, glass, or the like, and an absorbing pigment provided inside or on the surface of the light-transmitting substrate.

[0093] The color conversion element 130 may be used in devices other than the lighting device 100. For example, the color conversion element 130 may be used in a display, a projector, or the like.

[0094] In addition, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions of each embodiment within the scope of the present invention.

[0095] REFERENCE SIGNS LIST 100 Illumination device 110 White light source 112 Blue light emitting element 114 Yellow phosphor 120 First optical system 130 Color conversion element 140 Second optical system

Claims

1. A lighting device comprising: a white light source including a blue light emitting element and a yellow phosphor, and emitting a first white light; and a color conversion element that converts the first white light into a second white light, wherein, assuming that the average transmittance of the color conversion element in the range of 435 nm to 480 nm is TB, the average transmittance of the color conversion element in the range of 540 nm to 590 nm is TG, the color temperature (unit: K) of the first white light is T1, and the color temperature (unit: K) of the second white light is T2, the following relationships are satisfied: 2500≦(TG÷TB)×T2≦5000 and T1-T2≧300.

2. The lighting device according to claim 1, further comprising a first optical system disposed between said white light source and said color conversion element, said first optical system converting the first white light emitted from said white light source into parallel light.

3. The lighting device according to claim 1, further comprising a second optical system that projects the second white light emitted from the color conversion element.

4. The lighting device according to any one of claims 1 to 3, wherein the white light source includes a plurality of the blue light-emitting elements arranged in a two-dimensional matrix, and the yellow phosphor is disposed on the light emission side of the plurality of the blue light-emitting elements.

5. The lighting device according to any one of claims 1 to 3, wherein the blue light emitting element is a blue semiconductor laser element.

6. The lighting device according to any one of claims 1 to 3, wherein the color conversion element is a dichroic filter.

7. The lighting device according to any one of claims 1 to 3, wherein the minimum transmittance of the color conversion element in the range of 400 nm or more and 450 nm or less is smaller than the minimum transmittance of the color conversion element in the range of 525 nm or more and 575 nm or less.

8. The lighting device according to any one of claims 1 to 3, wherein the maximum value of the transmittance of the color conversion element in the range of 450 nm or more and 500 nm or less, and the maximum value of the transmittance of the color conversion element in the range of 600 nm or more and 750 nm or less, are 90% or more.

9. A color conversion element that converts a first white light into a second white light, wherein, when an average transmittance of the color conversion element in a range of 435 nm or more and 480 nm or less is defined as TB, an average transmittance of the color conversion element in a range of 540 nm or more and 590 nm or less is defined as TG, a color temperature (unit: K) of the first white light is defined as T1, and a color temperature (unit: K) of the second white light is defined as T2, the color conversion element satisfies 2500≦(TG÷TB)×T2≦5000 and T1-T2≧300.

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