Lighting device and color conversion element

Abstract

A lighting device includes (100): a white light source (110) that includes a blue light-emitting element and a yellow phosphor, and emits a first white light; and a color conversion element (130) that converts the first white light to a second white light. 2500 ≤ (TG / TB) × T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element (130) in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element (130) in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

Description

[Technical Field]

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

[0002] Patent Literature (PTL) 1 discloses an optical filter that includes an optical multi-layer film for which an average reflectance of light in a wavelength range of from green light to yellow light and a wavelength range of blue light is selectively enhanced. The optical filter disclosed in PTL 1 is described as being capable of enhancing color rendering properties while inhibiting light-emission efficiency from decreasing and color temperature from changing.[Citation List][Patent Literature]

[0003] [PTL 1] Japanese Patent No. 6058948[Summary of Invention][Technical Problem]

[0004] The present invention provides a lighting device and a color conversion element that can achieve both enhanced color rendering properties and reduced color temperatures.[Solution to Problem]

[0005] A lighting device according to one aspect of the present invention includes: a white light source that includes a blue light-emitting element and a yellow phosphor, and emits a first white light; and a color conversion element that converts the first white light to a second white light, wherein 2500 ≤ (TG / TB) × T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

[0006] A color conversion element according to one aspect of the present invention is a color conversion element that converts the first white light to a second white light, wherein 2500 ≤ (TG / TB) × T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.[Advantageous Effects of Invention]

[0007] According to the present invention, enhanced color rendering properties and reduced color temperatures can both be achieved.[Brief Description of Drawings]

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

[0009] Hereinafter, lighting devices and color conversion elements according to embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments described below each illustrate a specific example of the present invention. The numerical values, shapes, materials, elements, the arrangement and connection of the elements, steps, the order of the steps, etc., described in the following embodiments are mere examples, and are therefore not intended to limit the present invention. Accordingly, among elements in the following embodiments, those not appearing in any of the independent claims will be described as optional elements.

[0010] It should be noted that the figures are schematic diagrams and are not necessarily precise illustrations. Therefore, for example, the scaling, and so on, depicted in the drawings is not necessarily uniform. Moreover, elements that are substantially the same are given the same reference signs in the respective figures, and redundant descriptions may be omitted or simplified.

[0011] Furthermore, in the present specification, terms indicating relationships between elements, such as parallel and the like, terms indicating shapes of elements, and numerical ranges refer not only to their strict meanings, but also include variations that fall within an essentially equivalent range, such as a range of deviation of a few percent.

[0012] For example, in the present specification, note that "parallel light" as described here does not necessarily mean light that is completely parallel, and includes light that can be considered to be approximately parallel, or in other words, light that is substantially parallel, while also referring to light that may spread out or converge within a range of several percent.

[0013] Furthermore, in the present specification, ordinal numbers, such as "first", "second", and the like not only indicate the number or the order of elements, but are also used for the purpose of avoiding confusion and to better distinguish between similar types of elements.(Embodiment)[Configuration]

[0014] First, a configuration of a lighting device according to an embodiment will be described with reference to FIG. 1 through FIG. 4.

[0015] FIG. 1 is a schematic perspective view of lighting device 100 according to the embodiment. FIG. 2 is a diagram that illustrates a configuration of lighting device 100 according to the embodiment. FIG. 3 is a schematic plan view of white light source 110 of lighting device 100 according to the embodiment. FIG. 4 is a schematic cross-sectional view of white light-emitting element 111 of lighting device 100 according to the embodiment. Note that in FIG. 4, shading using diagonal lines that indicate a cross section has been omitted.

[0016] As illustrated in FIG. 1, lighting device 100 is, for example, a spotlight, and is attached to a wiring apparatus (for example, a wiring duct or a hook-and-twist ceiling outlet) provided in a ceiling or a wall. Lighting device 100 may be a down light or a ceiling light.

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

[0018] White light source 110 is a light source that emits white light L11. White light L11 is an example of a first white light. As illustrated in FIG. 3, white light source 110 includes a plurality of white light-emitting elements 111 that are arranged in a two-dimensional matrix. The plurality of white light-emitting elements 111 are arranged in an orderly manner in a matrix that has M rows and N columns. Here, M and N are two or more natural numbers. M = N may be satisfied, and, alternatively, M ≠ N may be satisfied. The space between each white light-emitting element 111 in a row direction and a column direction may be the same, or, alternatively, may be different. Although an outline of a range of space in which the plurality of white light-emitting elements 111 are arranged is rectangular, the range may be circular instead.

[0019] Each of the plurality of white light-emitting elements 111 has the same configuration. Specifically, as illustrated in FIG. 4, white light-emitting element 111 includes blue light-emitting element 112 and yellow phosphor 114. Yellow phosphor 114 is disposed on a side toward which blue light-emitting element 112 emits light.

[0020] Blue light-emitting element 112 emits blue light Lb. Blue light-emitting element 112 is, for example, a light-emitting diode (LED). Although blue light-emitting element 112 is, for example, a minute LED that measures 100 µm × 100 µm, this example is not limiting. Blue light-emitting element 112 may be a blue light semiconductor laser element.

[0021] Yellow phosphor 114 is a fluorescent substance that emits yellow light Ly as a result of being excited by blue light Lb. Mixed light that includes yellow light Ly and blue light Lb that passes through yellow phosphor 114 is white light L11 that is emitted from white light-emitting element 111. Although yellow phosphor 114 is a fluorescent substance, such as yttrium aluminum garnet (YAG), for example, this example is not limiting. Yellow phosphor 114 is provided in contact with a light exit surface of blue light-emitting element 112.

[0022] It should be noted that blue light-emitting element 112 and yellow phosphor 114 may be disposed apart from each other. Furthermore, blue light-emitting element 112 and yellow phosphor 114 need not be provided in one-to-one correspondence with each other. Furthermore, yellow phosphor 114 may be provided so as to cover a plurality of blue light-emitting elements 112. For example, for a plurality of blue light-emitting elements 112 that have been arranged in a two-dimensional matrix, a yellow fluorescent plate that entirely covers the plurality of blue light-emitting elements 112 may be disposed as yellow phosphor 114.

[0023] Although not illustrated in the figures, lighting device 100 includes a controller that controls light emission of the plurality of white light-emitting elements 111 (blue light-emitting elements 112). The controller independently controls each of the plurality of blue light-emitting elements 112. In other words, the controller can individually control the turning on, turning off, light-emission intensity, light-emission duration, and the like of each of the plurality of blue light-emitting elements 112. For example, by individually controlling the turning on and turning off of the plurality of blue light-emitting elements 112, it is possible to emit an illumination light in which each region has a different level of brightness or darkness.

[0024] The controller is implemented as an integrated circuit (IC) or a large-scale integration circuit (LSI), for example. Moreover, the integrated circuit is not limited to an LSI, and implementation through a dedicated circuit or a general-purpose processor is also possible. For example, the controller may be a microcontroller. For example, the microcontroller includes a non-volatile memory in which a program is stored, a volatile memory that is a temporary storage region for executing a program, an input / output port, a processor that executes a program, and the like. Furthermore, the controller may be a field programmable gate array (FPGA) that is programmable, or a reconfigurable processor that allows for reconfiguration of the connection and the setting of circuit cells inside an LSI. The functions executed by the controller may be implemented as software, and may be implemented as hardware.

[0025] First optical system 120 converts white light L11 emitted from white light source 110 to parallel light. As illustrated in FIG. 2, first optical system 120 converts white light L11 to white light L12 that is parallel light, and white light L12 is transmitted toward color conversion element 130. Although first optical system 120 is, for example, a single collimator lens, this example is not limiting. First optical system 120 may be implemented as a plurality of collimator lenses, and may include other optical elements, such as a mirror and / or a condenser lens.

[0026] In the present embodiment, as illustrated in FIG. 2, first optical system 120 is disposed between white light source 110 and color conversion element 130. First optical system 120 is disposed so as to entirely cover a light exit surface of white light source 110, and combines and converts white light L11 from each of the plurality of white light-emitting elements 111 to white light L12 that is parallel light. It should be noted that it is sufficient so long as first optical system 120 is optically disposed between white light source 110 and color conversion element 130. In other words, it is sufficient so long as first optical system 120 is disposed on an optical path of the first white light from white light source 110 to color conversion element 130. At least a portion of first optical system 120 need not be physically (mechanically) disposed between white light source 110 and color conversion element 130.

[0027] Color conversion element 130 is an element that converts the first white light to a second white light. The second white light is light that is a different color temperature than the first white light. Specifically, by inhibiting the transmission of specific wavelength components of the first white light, color conversion element 130 causes a second white light to be transmitted that is a different color temperature and has a different spectral distribution than the first white light.

[0028] In the present embodiment, as illustrated in FIG. 2, color conversion element 130 converts white light L12 to white light L21. White light L12 is an example of a first white light emitted from white light source 110, and has a spectrum that is substantially the same as white light L11. In other words, white light L12 and white light L11 have color temperatures that are substantially the same. White light L21 is an example of a second white light, and has a spectrum and a color temperature that are different than white light L12. The specific transmission spectrum of color conversion element 130 will be described later.

[0029] In the present embodiment, color conversion element 130 is an optical element for which spectral transmittance is adjusted by using reflected light. For example, color conversion element 130 is a dichroic filter. A dichroic filter includes a multi-layer structure in which layers of dielectric film with a high refractive index and layers of dielectric film with a low refractive index are alternately stacked on each other. A metal oxide film that includes SiO 2 , TiO 2 , Nb 2 O 5 , HfO 2 , and the like may be used as the dielectric film. By adjusting the materials used in the two types of dielectric film layers, the thickness of each film layer, the total number of layers, and the like, it is possible to achieve the desired transmission spectrum.

[0030] Second optical system 140 projects white light L21 that exits from color conversion element 130. As illustrated in FIG. 2, second optical system 140 converts white light L21 to white light L22 that is projected light, and white light L22 is transmitted outward. Although second optical system 140 is, for example, one or a plurality of projection lenses, this example is not limiting. Second optical system 140 may include other optical elements, such as a mirror and / or a condenser lens.

[0031] Housing 150 houses white light source 110, first optical system 120, color conversion element 130, and second optical system 140. Although housing 150 is, for example, an outer-shell housing that forms an outer shell of lighting device 100, and includes a plurality of components, such as a heat sink, this example is not particularly limited. The components included in housing 150 are made using resin or metal.

[0032] In housing 150, an opening is provided on a side toward which light is emitted (a normal direction of a main surface of a substrate) of white light source 110, and second optical system 140 is disposed to cover the opening. For example, when light-emission control is being individually performed for the plurality of blue light-emitting elements 112, since there is no need to provide a liquid-crystal device or a digital mirror device (DMD) in housing 150, such as in a typical projector, lighting device 100 can be miniaturized.[Color Conversion Element]

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

[0034] With respect to light in a visible spectrum, color conversion element 130 has high transmittance except in two wavelength bands. That is to say, the transmission spectrum of color conversion element 130 has two transmittance valleys, or in other words, wavelength bands in which transmittance is lower than a predetermined value. The predetermined value is, for example, 60 percent. Note that in the present specification, the visible spectrum is in a range of from 400 nm to 750 nm, inclusive.

[0035] Specifically, color conversion element 130 is designed such that transmittance is low for each of blue-light components with a wavelength of 450 nm or less and green-light components with a wavelength in a vicinity of 550 nm. For example, a minimum value of transmittance of color conversion element 130 in a range of from 400 nm to 450 nm, inclusive, is smaller than a minimum value of transmittance of color conversion element 130 in a range of from 525 nm to 575 nm, inclusive. Although the minimum value of transmittance of color conversion element 130 in a range of from 400 nm to 450 nm, inclusive, is no less than 10 percent and no more than 60 percent, this example is not limiting. The minimum value of transmittance of color conversion element 130 in a range of from 400 nm to 450 nm, inclusive, may be 50 percent or less, 40 percent or less, 30 percent or less, or 20 percent or less. Furthermore, although the minimum value of transmittance of color conversion element 130 in a range of from 525 nm to 575 nm, inclusive, is no less than 20 percent and no more than 70 percent, this example is not limiting. The minimum value of transmittance of color conversion element 130 in a range of from 525 nm to 575 nm, inclusive, may be 60 percent or less, 50 percent or less, or 40 percent or less. Furthermore, the minimum value of transmittance of color conversion element 130 in a range of from 525 nm to 575 nm, inclusive, may be 30 percent or more.

[0036] Furthermore, for example, a maximum value of transmittance of color conversion element 130 in a range of from 450 nm to 500 nm, inclusive, and a maximum value of transmittance of color conversion element 130 in a range of from 600 nm to 750 nm, inclusive, is 90 percent or more, but may be 95 percent or more, or 97 percent or more.

[0037] Where TB is an average transmittance of color conversion element 130 in a range of from 435 nm to 480 nm, inclusive, TG is an average transmittance of color conversion element 130 in a range of from 540 nm to 590 nm, inclusive. Here, Equation 1 as indicated below is satisfied. 2500 ≤ TG / TB × T 2 ≤ 5000

[0038] It should be noted that average transmittance is an average value of spectral transmittance (transmittance for each wavelength) in the corresponding range. By satisfying the above-mentioned Equation 1, it is possible to enhance the color rendering properties of white light L21 that exits from color conversion element 130.

[0039] Average color rendering index Ra of white light L12 before white light L12 is incident on color conversion element 130 is approximately 70. Since white light L12 is mixed light that includes blue light Lb from blue light-emitting element 112 and yellow light Ly from yellow phosphor 114, the blue-light components and yellow-light components become intensified, thereby causing the color rendering properties to be low.

[0040] In view of this, since color conversion element 130 is set such that the transmittance of blue-light components and yellow-light components of white light L12 is low, blue light and yellow light are inhibited from being transmitted. Accordingly, white light L21 after white light L21 passes through color conversion element 130 approaches a white light that is natural (sunlight) in which there are fewer undulations in terms of intensity spectrum. Thus, average color rendering index Ra of white light L21 after white light L21 passes through color conversion element 130 can be made to be 90 or greater.

[0041] Furthermore, color conversion element 130 is set with a blue light transmittance that is lower than a yellow light transmittance. In other words, since color conversion element 130 inhibits blue light from being transmitted, it is possible to cause the color temperature of the white light after the white light passes through to be low.

[0042] Specifically, the color temperature of white light L21 is lower than the color temperature of white light L12. Where T1 is the color temperature (unit of measurement: K) of white light L11 and white light L12, T2 is the color temperature (unit of measurement: K) of white light L21. Here, Equation 2 as indicated below is satisfied. T 1 − T 2 ≥ 300

[0043] For example, it should be noted that color temperature T1 of white light L12 may be 5000 K or greater, 5200 K or greater, 5500 K or greater, 5700 K or greater, or 6000 K or greater. Color temperature T2 of white light L21 is at least 300 K lower than such a color temperature T1 of white light L12.[Working examples]

[0044] Next, a plurality of specific working examples of color conversion element 130 will be described with reference to FIG. 5 through FIG. 14.

[0045] FIG. 5 is a diagram that illustrates transmittance of a color conversion element according to a comparative example and light intensity before and after light passes through the color conversion element. FIG. 6 through FIG. 11 are diagrams that illustrate transmittance of color conversion elements according to Working Example 1 through Working Example 6 and light intensity before and after light passes through the color conversion elements.

[0046] In FIG. 5 through FIG. 11, target values have been set for the color temperatures of white light after the white light has passed through the color conversion elements, and simulation results are illustrated of transmission spectrums of color conversion elements with spectral transmittances that have been designed to achieve the target values. In view of this, FIG. 12 through FIG. 14 each illustrate transmittance of a prototype (sample item) of a color conversion element for which data is shown in FIG. 7, FIG. 10, and FIG. 11 and light intensity before and after light passes through the prototype.

[0047] In each diagram, the horizontal axis represents the wavelength of light. The vertical axis represents transmittance or light intensity. Transmittance is represented as a ratio of light intensity of outgoing light to light intensity of incident light. Light intensity is represented using an arbitrary unit of measurement.

[0048] The spectrum of first white light incident on the color conversion element is the same for the comparative example and Working Example 1 through Working Example 6. Color temperature T1 of the first white light is 5500 K. For example, as illustrated in FIG. 5, the first white light has a first intensity peak of blue-light components and a second intensity peak of yellow-light components. The peak wavelength of the first intensity peak is approximately 447 nm. It should be noted that the peak wavelength is the wavelength at which light intensity reaches a maximum. The peak wavelength of the second intensity peak is approximately 555 nm. The maximum value of intensity of the first intensity peak is larger than the maximum value of intensity of the second intensity peak. Furthermore, the half bandwidth of the first intensity peak is narrower than the half bandwidth of the second intensity peak.

[0049] The target value of color temperature of the comparative example illustrated in FIG. 5 is 5500 K. In other words, the color conversion element according to the comparative example is designed with the aim of enhancing color rendering properties without changing the color temperature. The respective target values of Working Example 1 through Working Example 6 illustrated in FIG. 6 through FIG. 11 are 5000 K, 4500 K, 4000 K, 3500 K, 3000 K, and 3000 K.

[0050] TABLE 1 includes data on color temperature T2 of transmitted light (second white light), average transmittance TG in a range of from 540 nm to 590 nm, inclusive, average transmittance TB in a range of from 435 nm to 480 nm, inclusive, index A (= TG / TB × T2) of Equation 1, and index B (= T1 - T2) of Equation 2, as they relate to the comparative example and Working Example 1 through Working Example 6. [TABLE 1]Color temperature T2Average transmittance TGAverage transmittance TBIndex A (TG / TB) × T2Index B T1 - T2Comparative example5500K48%77%3428KOKWorking Example 15000K52%76%3421K500KWorking Example 24500K54%71%3422K1000KWorking Example 34000K53%64%3312K1500KWorking Example 43500K48%52%3230K2000KWorking Example 53000K40%31%3871K2500KWorking Example 63000K45%34%3970K2500K [Working Example 1]

[0051] The target value of color temperature of the color conversion element according to Working Example 1 illustrated in FIG. 6 is 5000 K. As a result, index B in TABLE 1 is 500 K, thereby satisfying the conditions of Equation 2.

[0052] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 1, transmittance is set to remain constant at 38 percent in a wavelength range of from 400 nm to 440 nm, inclusive. Furthermore, transmittance is set to remain constant at 52 percent in a wavelength range of from 540 nm to 585 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 460 nm to 525 nm, inclusive, and a range of from 610 nm to 750 nm, inclusive. In transitional portions of the transmittance curve (ranges where transmittance increases or decreases in conjunction with changes in wavelength), transmittance is set to change at a proportionally constant rate. As a result, in Working Example 1, average transmittance TG is 52 percent, average transmittance TB is 76 percent, and index A of TABLE 1 is 3421 K, thereby satisfying the conditions of Equation 1.[Working Example 2]

[0053] The target value of color temperature of the color conversion element according to Working Example 2 illustrated in FIG. 7 is 4500 K. As a result, index B in TABLE 1 is 1000 K, thereby satisfying the conditions of Equation 2.

[0054] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 2, transmittance is set to remain constant at 23 percent in a wavelength range of from 400 nm to 440 nm, inclusive. Furthermore, transmittance is set to remain constant at 53.5 percent in a wavelength range of from 535 nm to 585 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 460 nm to 515 nm, inclusive, and a range of from 606 nm to 750 nm, inclusive. In transitional portions of the transmittance curve, transmittance is set to change at a proportionally constant rate. As a result, in Working Example 2, average transmittance TG is 54 percent, average transmittance TB is 71 percent, and index A of TABLE 1 is 3422 K, thereby satisfying the conditions of Equation 1.[Working Example 3]

[0055] The target value of color temperature of the color conversion element according to Working Example 3 illustrated in FIG. 8 is 4000 K. As a result, index B in TABLE 1 is 1500 K, thereby satisfying the conditions of Equation 2.

[0056] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 3, transmittance is set to remain constant at 21.5 percent in a wavelength range of from 400 nm to 444 nm, inclusive. Furthermore, transmittance is set to remain constant at 48.1 percent in a wavelength range of from 535 nm to 575 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 464 nm to 515 nm, inclusive, and a range of from 596 nm to 750 nm, inclusive. In transitional portions of the transmittance curve, transmittance is set to change at a proportionally constant rate. As a result, in Working Example 3, average transmittance TG is 53 percent, average transmittance TB is 64 percent, and index A of TABLE 1 is 3312 K, thereby satisfying the conditions of Equation 1.[Working Example 4]

[0057] The target value of color temperature of the color conversion element according to Working Example 4 illustrated in FIG. 9 is 3500 K. As a result, index B in TABLE 1 is 2000 K, thereby satisfying the conditions of Equation 2.

[0058] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 4, transmittance is set to remain constant at 19.5 percent in a wavelength range of from 400 nm to 451 nm, inclusive. Furthermore, transmittance is set to remain constant at 41.2 percent in a wavelength range of from 531 nm to 574 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 471 nm to 511 nm, inclusive, and a range of from 595 nm to 750 nm, inclusive. In transitional portions of the transmittance curve, transmittance is set to change at a proportionally constant rate. As a result, in Working Example 4, average transmittance TG is 48 percent, average transmittance TB is 52 percent, and index A of TABLE 1 is 3230 K, thereby satisfying the conditions of Equation 1.[Working Example 5]

[0059] The target value of color temperature of the color conversion element according to Working Example 5 illustrated in FIG. 10 is 3000 K. As a result, index B in TABLE 1 is 2500 K, thereby satisfying the conditions of Equation 2.

[0060] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 5, transmittance is set to remain constant at 11.3 percent in a wavelength range of from 400 nm to 455 nm, inclusive. Furthermore, transmittance is set to remain constant at 29.9 percent in a wavelength range of from 520 nm to 550 nm, inclusive. Furthermore, transmittance is set to remain constant at 54.5 percent in a wavelength range of from 590 nm to 595 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 485 nm to 490 nm, inclusive, and a range of from 625 nm to 750 nm, inclusive. In transitional portions of the transmittance curve, transmittance is set to change at a proportionally constant rate. As a result, in Working Example 5, average transmittance TG is 40 percent, average transmittance TB is 31 percent, and index A of TABLE 1 is 3871 K, thereby satisfying the conditions of Equation 1.[Working Example 6]

[0061] The target value of color temperature of the color conversion element according to Working Example 6 illustrated in FIG. 11 is 3000 K. As a result, index B in TABLE 1 is 2500 K, thereby satisfying the conditions of Equation 2.

[0062] Furthermore, in the transmission spectrum of the color conversion element according to Working Example 6, transmittance is set to remain constant at 14.8 percent in a wavelength range of from 400 nm to 455 nm, inclusive. Furthermore, transmittance is set to remain constant at 28 percent in a wavelength range of from 536 nm to 552 nm, inclusive. Furthermore, transmittance is set to remain constant at 95 percent both in a wavelength range of from 485 nm to 496 nm, inclusive, and a range of from 608 nm to 750 nm, inclusive. In transitional portions of the transmittance curve, transmittance is set to change at a proportionally constant rate. As a result, in Working Example 6, average transmittance TG is 45 percent, average transmittance TB is 34 percent, and index A of TABLE 1 is 3970 K, thereby satisfying the conditions of Equation 1.[Prototypes]

[0063] From among the above-mentioned six working examples, the inventors of the present application created prototypes for Working Example 2, Working Example 5, and Working Example 6. The prototypes are dichroic filters, which have been set to match the transmission characteristics illustrated in each working example, by adjusting factors, such as by switching between two types of dielectric film materials and by changing the thickness of each layer and the number of layers or the like.

[0064] As illustrated in FIG. 12 through FIG. 14, although the transmission spectrum of each prototype forms a smoother shape when compared to the design values, each transmission spectrum generally follows the transmission spectrum of the corresponding working example. The parameters of color temperature T2 and the like of the prototypes are as indicated in TABLE 2 below. It should be noted that color temperature T1 of first white light that is incident light is 5534 K. [TABLE 2]PrototypeColor temperature T2Average transmittance TGAverage transmittance TBIndex A (TG / TB) × T2Index B T1 - T2Working Example 24214K54.9%72.5%3190K1320KWorking Example 53321K46.0%41.1%3720K2213KWorking Example 62844K43.5%34.7%3558K2690K

[0065] FIG. 15 is a diagram illustrating a relationship between color temperature and evaluation index of transmitted light of the color conversion element. In FIG. 15, the horizontal axis represents the color temperature of transmitted light and the vertical axis represents index A.

[0066] In FIG. 15, index A is plotted for 16 examples that include the above-mentioned Working Example 1 through Working Example 6 and three examples of prototypes, for a total of 19 examples. It should be noted that since color temperature T2 of transmitted light (second white light) is also dependent on the color temperature and the spectrum of incident light (first white light), an index A has been calculated for each of three different types of incident light. Each of the three different types of incident light respectively have a color temperature T1 of 5534 K, 5263 K, and 5684 K, and have a spectrum that is equivalent to the light intensity spectrum of light before the light is transmitted as indicated in FIG. 5 through FIG. 14.

[0067] As illustrated in FIG. 15, although there is slight variation in accordance to differences in color temperature and spectrum of the incident light, it can be identified that index A stays within a range of from 2500 K to 5000 K, inclusive, regardless of the color temperature of the transmitted light. In other words, by satisfying the relationships indicated in the above-mentioned Equation 1 and Equation 2, it is possible to achieve both enhanced color rendering properties and reduced color temperatures.[Summary]

[0068] As described above, a lighting device according to a first aspect of the present invention is, for example, the above-mentioned lighting device 100 that includes: white light source 110 that includes blue light-emitting element 112 and yellow phosphor 114, and emits a first white light; and color conversion element 130 that converts the first white light to a second white light. 2500 ≤ (TG / TB) × T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied, where: TB is an average transmittance of color conversion element 130 in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of color conversion element 130 in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

[0069] Accordingly, it is possible to achieve both enhanced color rendering properties and reduced color temperatures. In white light L11 emitted from white light source 110, which includes blue light-emitting element 112 and yellow phosphor 114, there is a tendency for the color temperature to become high due to the increased intensity of blue light components, thereby making it difficult to achieve a lighting device with reduced color temperatures. In view of this, it is possible to enhance color rendering properties and to change a high color temperature white light to a low color temperature white light by using color conversion element 130.

[0070] Furthermore, a lighting device according to a second aspect of the present invention is the lighting device according to the first aspect, further including: first optical system 120 that is disposed between white light source 110 and color conversion element 130, and converts the first white light emitted from white light source 110 to a parallel light.

[0071] Accordingly, white light L12 can be caused to enter from the front of color conversion element 130. Since the influence of angular dependencies of the transmittance of color conversion element 130 can be inhibited, it is possible to achieve the desired enhanced color rendering properties and reduced color temperatures.

[0072] Furthermore, a lighting device according to a third aspect of the present invention is the lighting device according to the first aspect or the second aspect, further including: second optical system 140 that projects the second white light that exits from color conversion element 130.

[0073] Accordingly, it is possible to cause white light with high color rendering properties and reduced color temperatures to be efficiently emitted at a desired region.

[0074] Furthermore, a lighting device according to a fourth aspect of the present invention is the lighting device according to any one of the first aspect to the third aspect, in which white light source 110 includes a plurality of blue light-emitting elements 112 arranged in a two-dimensional matrix, the plurality of blue light-emitting elements 112 each being blue light-emitting element 112. Yellow phosphor 114 is disposed on a side toward which the plurality of blue light-emitting elements 112 emit light.

[0075] Accordingly, by arranging a plurality of blue light-emitting elements 112 as a group in a narrow range, it is possible to miniaturize white light source 110 while enhancing intensity. By miniaturizing white light source 110, it is possible to also contribute to the miniaturization of the lighting device according to this aspect.

[0076] Furthermore, a lighting device according to a fifth aspect of the present invention is the lighting device according to any one of the first aspect to the fourth aspect, in which blue light-emitting element 112 is a blue light semiconductor laser element.

[0077] Accordingly, energy efficiency can be increased.

[0078] Furthermore, a lighting device according to a sixth aspect of the present invention is the lighting device according to any one of the first aspect to the fifth aspect, in which color conversion element 130 is a dichroic filter.

[0079] Accordingly, by adjusting the materials of the dielectric film layers included in the dichroic filter, thicknesses, the total number of layers, and the like, it is possible to easily achieve a color conversion element 130 that has the desired transmission spectrum.

[0080] Furthermore, a lighting device according to a seventh aspect of the present invention is the lighting device according to any one of the first aspect to the sixth aspect, in which a minimum value of transmittance of color conversion element 130 in a range of from 400 nm to 450 nm, inclusive, is smaller than a minimum value of transmittance of color conversion element 130 in a range of from 525 nm to 575 nm, inclusive.

[0081] Accordingly, the transmission of yellow light components and blue light components can be inhibited, and it is possible to achieve both enhanced color rendering properties and reduced color temperatures.

[0082] Furthermore, a lighting device according to an eighth aspect of the present invention is the lighting device according to any one of the first aspect to the seventh aspect, in which a maximum value of transmittance of color conversion element 130 in a range of from 450 nm to 500 nm, inclusive, and a maximum value of transmittance of color conversion element 130 in a range of from 600 nm to 750 nm, inclusive, are at least 90 percent.

[0083] Accordingly, light extraction efficiency can be increased.

[0084] Furthermore, a color conversion element according to a ninth aspect of the present invention is, for example, the above-mentioned color conversion element 130, in which color conversion element 130 converts a first white light to a second white light. 2500 ≤ (TG / TB) × T2 ≤ 5000 and T1 - T2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

[0085] Accordingly, it is possible to achieve both enhanced color rendering properties and reduced color temperatures. In white light L11 emitted from white light source 110, which includes blue light-emitting element 112 and yellow phosphor 114, there is a tendency for the color temperature to become high due to the increased intensity of blue-light components, thereby making it difficult to achieve a lighting device with reduced color temperatures. In view of this, it is possible to enhance color rendering properties and to change a high color temperature white light to a low color temperature white light by using color conversion element 130.(Other Embodiments, etc.)

[0086] Although the lighting device according to the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments.

[0087] For example, in the above embodiments, although white light source 110 includes a plurality of white light-emitting elements 111 that are arranged in a two-dimensional matrix, this example is not limiting. White light source 110 may be a single white light-emitting element.

[0088] Color conversion element 130 may be an optical element for which spectral transmittance is adjusted by using absorbed light. For example, color conversion element 130 may include a light-transmissive base material, such as resin or glass, and a light-absorbing dye that is provided on the interior or the surface of the light-transmissive base material.

[0089] Color conversion element 130 may be used by a device other than lighting device 100. For example, color conversion element 130 may be used by a display, a projector, or the like.

[0090] Forms obtained through various modifications to each of the foregoing embodiments that may be conceived by those skilled in the art, as well as forms realized by combining elements and functions in each of the foregoing embodiments without departing from the essence of the present invention are included within the scope of the present invention.[Reference Signs List]

[0091] 100lighting device 110white light source 112blue light-emitting element 114yellow phosphor 120first optical system 130color conversion element 140second optical system

Claims

1. A lighting device comprising: a white light source that includes a blue light-emitting element and a yellow phosphor, and emits a first white light; and a color conversion element that converts the first white light to a second white light, wherein 2500 ≤ TG / TB × T 2 ≤ 5000 and T 1 − T 2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

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

3. The lighting device according to claim 1, further comprising: a second optical system that projects the second white light that exits 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 blue light-emitting elements arranged in a two-dimensional matrix, the plurality of blue light-emitting elements each being the blue light-emitting element, and the yellow phosphor is disposed on a side toward which the plurality of blue light-emitting elements emit light.

5. The lighting device according to any one of claims 1 to 3, wherein the blue light-emitting element is a blue light 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 a minimum value of transmittance of the color conversion element in a range of from 400 nm to 450 nm, inclusive, is smaller than a minimum value of transmittance of the color conversion element in a range of from 525 nm to 575 nm, inclusive.

8. The lighting device according to any one of claims 1 to 3, wherein a maximum value of transmittance of the color conversion element in a range of from 450 nm to 500 nm, inclusive, and a maximum value of transmittance of the color conversion element in a range of from 600 nm to 750 nm, inclusive, are at least 90 percent.

9. A color conversion element that converts a first white light to a second white light, wherein 2500 ≤ TG / TB × T 2 ≤ 5000 and T 1 − T 2 ≥ 300 are satisfied, where: TB is an average transmittance of the color conversion element in a range of from 435 nm to 480 nm, inclusive; TG is an average transmittance of the color conversion element in a range of from 540 nm to 590 nm, inclusive; T1 is a color temperature of the first white light for which a unit of measurement is K; and T2 is a color temperature of the second white light for which a unit of measurement is K.

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