WO2024101023A1

WO2024101023A1 - Fluorescent light source device

Info

Publication number: WO2024101023A1
Application number: PCT/JP2023/035061
Authority: WO
Inventors: 正樹井上; 清幸蕪木
Original assignee: ウシオ電機株式会社
Priority date: 2022-11-09
Filing date: 2023-09-27
Publication date: 2024-05-16
Also published as: JP2024068970A

Abstract

Provided is a fluorescent light source device that includes an excitation light source and a fluorescent body, and that is capable of generating light that exhibits excellent color-rendering properties.　The fluorescent light source device comprises: an excitation light source that emits excitation light in the blue color region; a fluorescent plate that includes a fluorescent body in which Ce has been activated, and generates long-wavelength fluorescence by receiving the excitation light; a collimating optical system that at least reduces the divergence angle of the fluorescence; and a notch filter through which light that is emitted from the collimating optical system passes. The notch filter has a light incidence surface that is oriented substantially orthogonal to the optical axis of the principal rays of the light emitted from the collimating optical system, and a cut wavelength region in which the center wavelength thereof is in a range of 553–575 nm, and the half value width is in a range of 17–41 nm.

Description

Fluorescent light source device

The present invention relates to a fluorescent light source device that converts the wavelength of incident excitation light and emits the generated fluorescent light.

In light source devices that generate illumination light, the market may demand that the illumination light have high color rendering properties.

Patent Document 1 below discloses a light source device that includes an excitation light-emitting element composed of a GaN-based LED element, and a wavelength control optical member that includes a phosphor that receives light emitted from the light-emitting element and emits fluorescence. The wavelength control optical member disclosed in Patent Document 1 has a multi-layer structure, and specifically includes a first wavelength conversion layer in which a green fluorescent dye is dispersed within a matrix resin, a second wavelength conversion layer in which a red fluorescent dye is dispersed within a matrix resin, and a wavelength selection layer in which a light-absorbing dye is dispersed within a matrix resin.

According to Patent Document 1, the wavelength control optical component with the above structure is capable of improving color rendering by absorbing yellow light, which reduces color rendering, with a light absorbing pigment and a red fluorescent pigment, and emitting red light with the red fluorescent pigment.

Patent document 2 also discloses a technique for cutting out red light using a dichroic mirror that functions as a notch filter to improve color reproducibility.

JP 2017-138534 A Patent No. 5928383

The method of Patent Document 1 improves color rendering by absorbing light in the visible range using a phosphor or a dye-absorbing dye. As a result, a large amount of light is absorbed in the wavelength control optical component, and it is necessary to increase the output of the excitation light source to obtain a high light output, resulting in insufficient light utilization efficiency.

The method of Patent Document 2 has a structure in which a dichroic mirror functions as a notch filter, and is arranged at a 45° inclination with respect to the optical axis. A notch filter is formed by stacking multiple dielectric layers with different refractive indices. To narrow the cut wavelength range of the notch filter, it is necessary to increase the number of layers (number of films). On the other hand, if the number of films is too large, the stress on the substrate holding the dielectric multilayer film increases, which may induce deformation or cracking of the substrate. For this reason, there is a natural limit to the number of layers that can be stacked as a dielectric multilayer film.

When a notch filter is placed with its light incidence surface tilted at 45° with respect to the optical axis, the chief ray of light incident on this notch filter passes through the notch filter at a 45° inclination with respect to the lamination direction of the dielectric multilayer film. This means that, compared to when the chief ray of light is incident in the normal direction of the light incidence surface of the notch filter, in order to pass the same optical path length through the notch filter, the thickness of the notch filter needs to be made thicker; in other words, the number of layers needs to be increased. However, as mentioned above, there is a limit to the number of layers that can be stacked as a dielectric multilayer film. Therefore, a notch filter with its light incidence surface tilted at 45° with respect to the optical axis is structurally unable to sufficiently narrow the cut wavelength range.

As a result of the inventor's intensive research, it has been confirmed that the color rendering property decreases as the cut wavelength range becomes wider. For these reasons, it is difficult to realize a light source device that exhibits extremely high color rendering property using the technology proposed in Patent Document 2.

In view of the above problems, the present invention aims to enable the generation of light with high color rendering properties in a light source device that includes an excitation light source and a phosphor.

The fluorescent light source device according to the present invention comprises:
an excitation light source that emits excitation light in the blue region;
a fluorescent plate including a Ce-activated phosphor and configured to receive the excitation light and generate fluorescence having a longer wavelength than the excitation light;
a collimating optical system for reducing at least the divergence angle of the fluorescent light;
a notch filter through which the light emitted from the collimating optical system passes,
the notch filter is disposed such that a light incident surface thereof is oriented substantially perpendicular to an optical axis of a chief ray of light emitted from the collimating optical system;
The cut wavelength range of the notch filter has a center wavelength in the range of 553 nm to 575 nm and a half width in the range of 17 nm to 41 nm;
The first feature of the present invention is that the light guided to the downstream utilization optical system via the notch filter is a composite light of the fluorescent light and light in the blue region, and has an average color rendering index (Ra value) of 85 or more.

Further, the fluorescent light source device according to the present invention is
an excitation light source that emits excitation light;
a fluorescent plate including a Ce-activated phosphor and configured to receive the excitation light and generate fluorescence having a longer wavelength than the excitation light;
a collimating optical system for reducing at least the divergence angle of the fluorescent light;
a notch filter through which the light emitted from the collimating optical system passes;
a blue light source that inputs superimposed light of a blue range onto an optical path of the fluorescence emitted from the fluorescent plate,
the notch filter is disposed such that a light incident surface thereof is oriented substantially perpendicular to an optical axis of a chief ray of light emitted from the collimating optical system;
The cut wavelength range of the notch filter has a center wavelength in the range of 553 nm to 575 nm and a half width in the range of 17 nm to 41 nm;
A second feature of the present invention is that the light guided to the downstream utilization optical system via the notch filter is a composite light of the fluorescent light and light in the blue region, and has an average color rendering index (Ra value) of 85 or more.

The phosphor may be a Ce-activated oxide phosphor or a Ce-activated _nitride phosphor. A specific example may be _one _or _more selected from the group consisting of _LSN ( _La3Si6N11 :Ce2 ⁺ , (La,Y) _3Si6N11 : ^Ce2 ⁺ ), CSO ( _CaSc2O4 : _Ce3 ⁺ ₎ , LuAG ( _Al5O12Lu3 :Ce2 ^{+), and YAG (Al5O12Y3:Ce2+} ₎ _. _Among the above-listed materials, LSN is particularly preferred.

In addition to Ce-activated phosphors, there are also Eu-activated and Gd-activated phosphors. However, compared to Ce, the electron orbitals of Eu and Gd are more susceptible to heat and deexcitation is more likely to occur. As a result, thermal quenching is large and the luminous efficiency is reduced. Therefore, from the perspective of achieving both high color rendering and high brightness, it is preferable to use Ce as the material activated in the phosphor.

With the above structure, the divergence angle of the fluorescence emitted from the fluorescent plate is reduced through a collimating optical system, and then the fluorescence is incident on a notch filter whose light incidence surface is formed in a direction substantially perpendicular to the optical axis of the principal ray. As a result, the wavelength range of the fluorescence cut by the notch filter can be narrowed.

Specifically, the cut wavelength range of the notch filter can be set so that the center wavelength is in the range of 553 nm to 575 nm, and the half-width is in the range of 17 nm to 41 nm. By arranging such a notch filter, the color rendering of the light that passes through the filter and is then incident on the downstream optical system is improved. The light that is incident on this optical system is a composite light of fluorescent light and light in the blue range, and an extremely high average color rendering index (Ra value) of 85 or more is achieved. This Ra value is a high value that has not been easily achieved with conventional fluorescent light source devices that include a phosphor and an excitation light source. The chromaticity y of the composite light is preferably in the range of 0.283 to 0.373.

The Ra value of the synthetic light can be measured by a method conforming to the method specified in JIS Z 8726 (method for evaluating the color rendering properties of light sources). The chromaticity y value of the synthetic light can be measured by a method conforming to the method specified in, for example, JIS Z 8724 (method for measuring color - light source color).

Note that "the light incident surface of the notch filter is substantially perpendicular to the optical axis of the chief ray of the light emitted from the collimating optical system" means that the angle between the normal to the light incident surface and the optical axis of the chief ray of the light emitted from the collimating optical system is within the range of -5° to +5°, and more preferably within the range of -3° to +3°.

As an example of _the fluorescent plate, a sintered binder made of inorganic compounds such as _CaF2 , _BaF2 , _MgF2 , ZnS, _Al2O3 , MgO, _ZrO2 , ZnO, _TiO2, etc., in which the particulate fluorescent material is dispersed and sintered can be used. Among the inorganic compounds listed above, oxide materials are particularly preferred as the binder material, with _Al2O3 being particularly preferred. When a nitride fluorescent material is used as the fluorescent material, _MgO is particularly preferred as the binder material.

In the case of the first characteristic configuration described above, in which a light source emitting blue light is used as the excitation light source, the light source device may emit a composite light of the blue light emitted from the excitation light source and the fluorescence emitted from the fluorescent plate. In addition, in this configuration, a separate blue light source that further emits blue light may be prepared, and the blue light emitted from the blue light source may be superimposed on the fluorescence emitted from the fluorescent plate, and the resulting composite light may be emitted from the light source device.

On the other hand, in the case of the second characteristic configuration described above, a separate blue light source that emits blue light is provided, and the blue light emitted from the blue light source is superimposed on the fluorescence emitted from the fluorescent plate, and the resulting composite light is emitted from the light source device. For this reason, the excitation light source does not necessarily have to be a light source that emits light in the blue range, and can be, for example, a light source that emits violet light or ultraviolet light. Furthermore, the position where the light in the blue range is superimposed can be between the notch filter and the fluorescent plate, or a position behind the fluorescent plate.

The collimating optical system may have a light entrance surface or light exit surface formed as a flat surface, and the notch filter may be disposed on the flat surface.

The above configuration allows the collimating optical system and the notch filter to be integrated, making it possible to reduce the size of the device.

The fluorescent light source device of the present invention can generate light that exhibits high color rendering properties.

1 is a diagram illustrating a schematic configuration of an embodiment of a fluorescent light source device. 1 is a diagram showing an example of a transmission spectrum of a notch filter. 4 is a schematic cross-sectional view for explaining the structure of a fluorescent plate. FIG. FIG. 4 is a partially enlarged view of FIG. 3 . 13 is a graph in which the spectrum of synthetic light L1 and the transmission spectrum of notch filter 20 are superimposed when blue light source 9 is an LED. 13 is a graph in which the spectrum of the synthetic light L1 and the transmission spectrum of the notch filter 20 are superimposed when the blue light source 9 is a laser diode. 13 is a graph showing the relationship between the y value and the Ra value of the combined light L1 when the blue light source 9 is an LED, the material of the phosphor 16 contained in the phosphor plate 10, and the presence or absence of the notch filter 20 are changed. 13 is a graph showing the relationship between the y value and the Ra value of the combined light L1 when the blue light source 9 is a laser diode, the material of the phosphor 16 contained in the phosphor plate 10, and the presence or absence of the notch filter 20 are changed. 11 is a graph showing the relationship between the half width of the cut wavelength range of the notch filter 20 and the Ra value of the synthetic light L1. 11 is a graph showing the relationship between the minimum transmittance of light within the cut wavelength band of the notch filter 20 and the Ra value of the synthetic light L1. 11 is a graph showing the relationship between the center wavelength of the cut wavelength range of the notch filter 20 and the Ra value of the synthetic light L1. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 11 is a diagram illustrating a configuration example of a fluorescent light source device according to another embodiment. 13 is a graph in which the spectrum of the combined light L1 and the transmission spectrum of the notch filter 20 are superimposed when the blue light source 9 is an LED and the fluorescent plate contains two types of fluorescent materials.

The configuration of the fluorescent light source device of the present invention will be described with reference to the drawings. Note that in each of the following figures, the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios. Furthermore, the numbers on the drawings do not necessarily match the actual numbers.

FIG. 1 is a diagram showing a schematic configuration of one embodiment of a fluorescent light source device. The fluorescent light source device 1 shown in FIG. 1 includes an excitation light source 5, a collimating optical system 7, a fluorescent plate 10, and a notch filter 20.

Furthermore, the fluorescent light source device 1 of this embodiment includes a blue light source 9 that emits blue light, a reflecting mirror 41, and a dichroic mirror 43.

In this embodiment, the emission wavelength of the excitation light source 5 is not limited as long as it is a wavelength capable of exciting the phosphor mounted on the fluorescent plate 10, but is typically in the blue, violet, or ultraviolet range. As a specific example, the excitation light source 5 includes a semiconductor laser element that emits light in the blue range with a wavelength of 445 nm to 465 nm. The excitation light source 5 may include an optical system such as a collimating lens as necessary.

Dichroic mirror 43 is designed to reflect at least blue light and transmit light with longer wavelengths than blue light. In this specification, blue light refers to light in the wavelength range of 420 nm to 500 nm, purple light refers to light in the wavelength range of 370 nm to 420 nm, and ultraviolet light refers to light in the wavelength range of less than 370 nm.

In the fluorescent light source device 1 of this embodiment shown in FIG. 1, excitation light L5 in the blue range from the excitation light source 5 is guided to one main surface of the fluorescent plate 10 (the main surface opposite to the side on which the substrate 11 is installed) via a reflecting mirror 41 and a dichroic mirror 43. The phosphor contained in the fluorescent plate 10 is excited by the excitation light L5 and emits fluorescent light L10. The divergence angle of the fluorescent light L10 is reduced via the collimating optical system 7, and then it is typically converted into parallel light, and then passes through the notch filter 20.

The notch filter 20 significantly reduces the light intensity of components in the designed cut wavelength range of the incident light, while hardly reducing the light output of wavelength components outside the cut wavelength range. The cut wavelength range of the notch filter 20 is designed so that the center wavelength falls within the range of 553 nm to 575 nm and the half width falls within the range of 17 nm to 41 nm.
That is, the cut wavelength range of the notch filter 20 provided in the fluorescent light source device 1 is an extremely narrow band.

As shown in FIG. 1, the fluorescence L10, which has been converted into nearly parallel light by the collimating optical system 7, enters the notch filter 20. In other words, the light incidence surface of the notch filter 20 is oriented in a direction substantially perpendicular to the optical axis of the chief ray of the fluorescence L10 emitted from the collimating optical system 7. Therefore, unlike the configuration of Patent Document 2, the cut wavelength range of the notch filter 20 can be narrowed.

The fluorescence L10, which has passed through the notch filter 20 and has a reduced light intensity of the components in the cut wavelength range, is combined with the blue light L9 emitted from the blue light source 9. This combined light L1 is guided to the downstream utilization optical system 50. An LED or a laser diode can be used as the blue light source 9. The utilization optical system 50 is any optical system that utilizes the combined light L1 emitted from the fluorescent light source device 1.

In the example shown in FIG. 1, a collimating optical system 45 is provided to reduce the divergence angle of the blue light L9 emitted from the blue light source 9, but it is optional whether or not to provide this collimating optical system 45.

An example of the fluorescent plate 10 provided in the fluorescent light source device 1 of this embodiment will be described with reference to Figs. 3 and 4. Fig. 3 is a cross-sectional view showing a schematic configuration of the fluorescent plate 10 and the substrate 11. Fig. 4 is an enlarged view of a portion of Fig. 3.

In the example shown in Figure 3, the fluorescent plate 10 is fixed to the substrate 11 via a bonding layer 12.

The substrate 11 is provided to dissipate heat generated by the fluorescent plate 10, and is made of a material with a thermal conductivity of, for example, 90 [W/m·K] or more, specifically, for example, 230 to 400 [W/m·K]. Examples of such materials include Cu, copper compounds (MoCu, CuW, etc.), Al, and AlN. The thickness of the substrate 11 is, for example, 0.5 mm to 5 mm. From the standpoint of heat dissipation, it is preferable that the surface area of the substrate 11 is larger than the area of the fluorescent plate 10.

The bonding layer 12 is a layer that bonds the substrate 11 and the fluorescent plate 10, and is made of, for example, a solder material. From the viewpoint of heat dissipation, it is preferable that the material that constitutes the bonding layer 12 has, for example, a thermal conductivity of 40 [W/m·K] or more. More specifically, for example, cream solder made by mixing flux and other impurities with materials such as Sn and Pb in a cream (paste) form, Sn-Ag-Cu solder, Au-Sn solder, etc. can be used. The thickness of the bonding layer 12 is, for example, 20 μm to 200 μm.

Although not shown, in order to further improve the bond between the substrate 11 and the bonding layer 12, a metal film made of Ni/Au film formed by, for example, a plating method may be formed between the substrate 11 and the bonding layer 12. The thickness of this metal film may be, for example, Ni/Au = 1000 nm to 5000 nm/30 nm to 1000 nm.

In the example shown in FIG. 1, the surface on which the excitation light L5 is incident on the fluorescent plate 10 and the surface on which the fluorescent light L10 is extracted from the fluorescent plate 10 and used are the same surface. In other words, even if the fluorescent light L10 is emitted from the surface on the substrate 11 side of the fluorescent plate 10, the use of this fluorescent light L10 is not planned, and the efficiency of use is reduced. From this perspective, in the example shown in FIG. 3, a reflective layer 13 is provided on the upper surface of the substrate 11. The reflective layer 13 is provided to reflect the fluorescent light L10 generated by the fluorescent plate 10 and proceed toward the substrate 11 side, and to guide it to the main surface on the light extraction side. The reflective layer 13 can be composed of, for example, a metal film such as Al or Ag, or an increased reflection film in which a dielectric multilayer film is formed on the metal film.

However, as will be described later with reference to Figure 16, if the surface of the fluorescent plate 10 where the excitation light L5 is incident is different from the surface where the fluorescent light L10 is extracted, the reflective layer 13 is not necessary.

As an example, the fluorescent plate 10 has a rectangular flat plate-like structure when viewed in a direction perpendicular to the surface of the substrate 11. The fluorescent plate 10 has a thickness of, for example, 0.05 mm to 1 mm. In the example shown in FIG. 4, the fluorescent plate 10 includes a phosphor 16, a binder 17, and pores 18.
As shown in FIG. 3, the light extraction surface of the fluorescent plate 10 may have a moth-eye structure 15 formed by processing into fine projections and recesses.

The phosphor 16 is a Ce- _{activated oxide phosphor or a Ce-activated nitride phosphor. As a specific example, one or more materials selected from the group consisting of LSN (La3Si6N11} _: _Ce2 ₊ _, ⁽ ^La , _Y ) _3Si6N11 :Ce2+), CSO ( _CaSc2O4 _: _Ce3 ⁺ ), LuAG ( _Al5O12Lu3 :Ce2 ⁺ ), and YAG ( _Al5O12Y3 : _Ce2 ⁺ ) can be used. Among the above-listed materials, LSN _is particularly preferable.

As shown in FIG. 4, phosphor 16 is in the form of particles and is dispersed within binder 17. The particle size of phosphor 16 is 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less, and particularly preferably 10 μm or less. There is no particular lower limit for the particle size of phosphor 16, but it is generally 1 μm or more.

The _binder 17 is composed of an inorganic compound. As a specific example, the binder 17 is composed of one or more of _CaF2 , _BaF2 , _MgF2 , ZnS, _Al2O3 , MgO, _ZrO2 , _ZnO , and _TiO2 . Among the above examples of materials, alumina ( _Al2O3 ) is preferable. When a nitride phosphor is combined, MgO is particularly preferable as the material of the binder 17. The fluorescent plate 10 is a sintered body of inorganic particles, which are the constituent material of the binder 17, and particles of the constituent material of the phosphor 16. The pores 18 contained in the fluorescent plate 10 are generated during the sintering process, but it is also possible to make the structure completely free of pores 18 by changing the profile of the sintering process.

The mass ratio of the binder 17 contained in the fluorescent plate 10 is preferably 30% to 70% by mass or less, and more preferably 50% to 90% by mass. The mass ratio of the binder 17 contained in the fluorescent plate 10 refers to the ratio of the mass of the binder 17 to the total mass of the phosphor 16 and the binder 17.

The relative density of the fluorescent plate 10 is preferably 80.4% to 99.5%. The relative density of the fluorescent plate 10 is the ratio of the apparent density to the theoretical density of the fluorescent plate 10, which is a sintered body, and can be measured, for example, by a method conforming to JIS R 1634 (Method of measuring density and open porosity of sintered fine ceramics). In other words, the fluorescent plate 10 can include pores 18 with a content of 0.5% to 19.6%. The inclusion of pores 18 in the fluorescent plate 10 creates a refractive index difference at the interface between the phosphor 16 or binder 17 and the pores 18, making it easier to refract the fluorescence L10 generated within the fluorescent plate 10 to the main surface on the light extraction side.

Figure 5 is a graph superimposing the spectrum of the synthetic light L1 and the transmission spectrum of the notch filter 20 when the phosphor 16 contained in the fluorescent plate 10 is LSN (fluorescence peak wavelength is 535 nm), the binder 17 is alumina, and the blue light source 9 is an LED with a peak wavelength of 455 nm. A filter with the transmission spectrum shown in Figure 2 was used as the notch filter 20. As mentioned above, since the synthetic light L1 is light that has passed through the notch filter 20, the light intensity in the vicinity of 553 nm to 575 nm, which is the cut wavelength range of the notch filter 20, is significantly reduced.

When the synthetic light L1 obtained at this time was measured using a method conforming to JIS Z 8724 (method of measuring color - light source color), the chromaticity y value was 0.33. Furthermore, when the synthetic light L1 was measured using a method conforming to JIS Z 8726 (method of evaluating the color rendering properties of light sources), an extremely high average color rendering index (Ra value) of 92 was obtained.

Figure 6 is a graph superimposing the spectrum of the synthetic light L1 and the transmission spectrum of the notch filter 20 when the phosphor 16 contained in the fluorescent plate 10 is LSN (fluorescence peak wavelength is 535 nm), the binder 17 is alumina, and the blue light source 9 is a laser diode with a peak wavelength of 460 nm. A filter with the transmission spectrum shown in Figure 2 was used as the notch filter 20. As mentioned above, since the synthetic light L1 is light that has passed through the notch filter 20, the light intensity in the vicinity of 553 nm to 575 nm, which is the cut wavelength range of the notch filter 20, is significantly reduced.

When the synthetic light L1 obtained at this time was measured using a method conforming to JIS Z 8724, the chromaticity y value was 0.34. Furthermore, when the synthetic light L1 was measured using a method conforming to JIS Z 8726, an extremely high Ra value of 89.8 was obtained.

The reason why extremely high color rendering is achieved by the synthetic light L1 obtained by the fluorescent light source device 1 of this embodiment is unclear, but it is presumed that this is because the spectrum of the fluorescence L10 generated by excitation with the excitation light L5 has a reduced intensity in the wavelength range between the green and red ranges, near 553 nm to 575 nm. The synthetic light L1, which is obtained by combining the fluorescence L10, whose light intensity in the cut wavelength range near 553 nm to 575 nm is significantly reduced, with the blue light L9, essentially simulates a state in which blue light, green light, and red light are superimposed, and it is presumed that this results in high color rendering.

7 is a graph showing the relationship between the y value and the Ra value measured when the material of the phosphor 16 contained in the fluorescent plate 10 is YAG or LSN, and when the notch filter 20 is provided and when the notch filter 20 is not provided. The y value was changed by adjusting the relative value of the light output of the excitation light source 5 and the blue light source 9 to change the target color temperature.
The Ra value was measured using synthetic light according to a method in accordance with JIS Z 8726. As the blue light source 9, an LED with a peak wavelength of 455 nm was used.

When the notch filter 20 was provided, verification was performed on four types of phosphors 16 contained in the fluorescent plate 10: LSN (referred to as "LSN-1"), in which the peak wavelength of the fluorescence L10 was set to 535 nm; LSN (referred to as "LSN-2"), in which the peak wavelength of the fluorescence L10 was set to 540 nm; YAG (referred to as "YAG-1"), in which the peak wavelength of the fluorescence L10 was set to 540 nm; and YAG (referred to as "YAG-2"), in which the peak wavelength of the fluorescence L10 was set to 545 nm. On the other hand, when the notch filter 20 was not provided, verification was performed on two types of phosphors 16 contained in the fluorescent plate 10: YAG-1 and LSN-1.

According to FIG. 7, when the notch filter 20 is not provided, the Ra value of the synthetic light L1 falls below 80 regardless of the y value. On the other hand, when the notch filter 20 is provided, it can be seen that an extremely high Ra value of 85 or more is obtained for any phosphor when the chromaticity y value of the synthetic light L1 is within the range of 0.283 to 0.396. Furthermore, when comparing the cases where the phosphor is YAG and where it is LSN, a higher Ra value is obtained with LSN. This is thought to be because the fluorescence L10 emitted from LSN contains more red components than the fluorescence L10 emitted from YAG. When the chromaticity y value is within the range of 0.283 to 0.396, the color temperature of the synthetic light L1 is 5100K to 9100K.

Figure 8 is a graph showing the relationship between the y value and the Ra value measured in the same manner as in Figure 7, using a laser diode with a peak wavelength of 460 nm as the blue light source 9. Figure 8 confirms that when the blue light source 9 is a laser diode, as in the case of an LED, the Ra value of the synthetic light L1 falls below 80 regardless of the y value when the notch filter 20 is not provided. On the other hand, when the notch filter 20 is provided, it can be seen that an extremely high Ra value of 85 or more is obtained for all phosphors when the chromaticity y value of the synthetic light L1 is within the range of 0.280 to 0.373. Note that when the chromaticity y value is within the range of 0.283 to 0.373, the color temperature of the synthetic light L1 is 5400K to 8300K.

Table 1 shows the relationship between the half-width of the cut wavelength range of the notch filter 20 and the Ra value of the synthetic light L1 when the half-width is changed in a case where an LED with a peak wavelength of 462 nm is used as the blue light source 9 and LSN-2 is used as the phosphor 16 contained in the fluorescent plate 10. Note that FIG. 9 is a graph showing the results when the center wavelength of the cut wavelength range of each notch filter 20 is fixed at 564 nm and only the half-width is designed to be changed.

As shown in Figure 9, the Ra value of the synthetic light L1 can be increased by designing the cut wavelength range of the notch filter 20 to have a half-width in the range of 17 nm to 41 nm. If the half-width is too narrow, the light components in the wavelength range that should be cut to achieve high color rendering are not cut, and it is believed that the color rendering is degraded. Conversely, if the half-width is too wide, the light components in the wavelength range that should not be cut to achieve high color rendering are cut, and it is believed that the color rendering is degraded.

The following results can be obtained from Table 1.

When the center wavelength of the cut wavelength range of the notch filter 20 is 553 nm, if the half-width of the cut wavelength range is 19 nm to 23 nm, the Ra value of the synthetic light L1 exceeds 85. When the half-width is 18 nm, the Ra value is 84.4, which can be considered to be substantially equivalent to 85. By setting the half-width to 17 nm to 25 nm, the Ra value can be made 84 or more. Even when the Ra value is in the range of 84 to 85, the color rendering value is lower than when the Ra value is 85 or more, but this is a high value that could not be easily achieved with conventional fluorescent light source devices that include a phosphor and an excitation light source.

When the center wavelength of the cut wavelength range of the notch filter 20 is 555 nm, if the half-width of the cut wavelength range is 18 nm to 27 nm, the Ra value of the synthetic light L1 exceeds 85. When the half-width is 17 nm, the Ra value is 84.9, which can be considered to be substantially equivalent to 85. By setting the half-width to 17 nm to 28 nm, the Ra value can be made 84 or more. Even when the Ra value is in the range of 84 to 85, the color rendering value is lower than when the Ra value is 85 or more, but this is a high value that could not be easily achieved with conventional fluorescent light source devices that include a phosphor and an excitation light source.

When the center wavelength of the cut wavelength range of the notch filter 20 is 560 nm, if the half-width of the cut wavelength range is 17 nm to 31 nm, the Ra value of the synthetic light L1 exceeds 85. In particular, if the half-width is 23 nm to 25 nm, the Ra value of the synthetic light L1 reaches approximately 90. Note that if the half-width is 16 nm or 32 nm, the Ra is 84.5, which can be considered to be 85 when rounded off to the first decimal place. By setting the half-width to 16 nm to 32 nm, the Ra value can be made 84 or more.

When the center wavelength of the cut wavelength range of the notch filter 20 is 565 nm, if the half-width of the cut wavelength range is 18 nm to 35 nm, the Ra value of the synthetic light L1 exceeds 85. In particular, if the half-width is 23 nm to 29 nm, the Ra value of the synthetic light L1 reaches approximately 90. When the half-width is 17 nm, the Ra is 84.5, which can be considered to be 85 when rounded off to the first decimal place. By setting the half-width to 17 nm to 36 nm, the Ra value can be made 84 or more.

When the center wavelength of the cut wavelength range of the notch filter 20 is 570 nm, if the half-width of the cut wavelength range is 21 nm to 39 nm, the Ra value of the synthetic light L1 exceeds 85. In particular, if the half-width is 28 nm to 32 nm, the Ra value of the synthetic light L1 reaches approximately 90. When the half-width is 20 nm or 40 nm, the Ra is 84.8, which can be considered to be 85 when rounded off to the first decimal place. By setting the half-width to 20 nm to 41 nm, the Ra value can be made 84 or more.

When the center wavelength of the cut wavelength range of the notch filter 20 is 575 nm, if the half-width of the cut wavelength range is 32 nm or 34 nm, the Ra value of the synthetic light L1 exceeds 85. If the half-width is 30 nm or 36 nm, the Ra is 84.8, and if rounded to the first decimal place, the Ra can be considered to be 85. Also, by setting the half-width to 30 nm to 36 nm, the Ra can be made 84 or more.

On the other hand, when the center wavelength of the cut wavelength range of the notch filter 20 is 550 nm or 580 nm, the Ra value of the synthetic light L1 could not be increased to 83 or more even by adjusting the half-width of the cut wavelength range.

Figure 10 is a graph evaluating the effect on the Ra value of the synthetic light L1 when the degree of reduction in light belonging to the cut wavelength range of the notch filter 20 is changed when an LED with a peak wavelength of 462 nm is used as the blue light source 9 and LSN-2 is used as the phosphor 16 contained in the fluorescent plate 10. Specifically, the horizontal axis is the transmittance for light of the central wavelength in the cut wavelength range of the notch filter 20, and the vertical axis is the Ra value of the synthetic light L1.

According to FIG. 10, it can be seen that if the transmittance is at least 33% or less, a synthetic light L1 with a high Ra value can be obtained.

Figure 11 is a graph evaluating the effect on the Ra value of the synthetic light L1 when the central wavelength of the cut wavelength range of the notch filter 20 is changed when an LED with a peak wavelength of 462 nm is used as the blue light source 9 and LSN-2 is used as the phosphor 16 contained in the fluorescent plate 10. Specifically, each notch filter 20 was designed so that the half-width of the cut wavelength range of the notch filter 20 was fixed at 25 nm and only the central wavelength was changed.

According to FIG. 11, it can be seen that by designing the notch filter 20 so that the center wavelength of the cut wavelength range is within the range of 553 nm to 575 nm, the Ra value of the synthetic light L1 can be increased.

[Another embodiment]
The following describes another embodiment of the fluorescent light source device 1. In the following drawings, the same elements as those in FIG.

<1> As in the fluorescent light source device 1 shown in FIG. 12, the notch filter 20 may be disposed downstream of the location where the blue light L9 is combined with the fluorescent light L10. In the example of FIG. 12, the notch filter 20 is disposed downstream of the dichroic mirror 43.

<2> The notch filter 20 may be installed as an integral part of a refractive optical system that changes the direction of light travel.

The fluorescent light source device 1 shown in FIG. 13 is equipped with a focusing optical system 46. This focusing optical system 46 is arranged for the purpose of focusing and guiding the composite light L1 generated by the fluorescent light source device 1 toward the downstream utilization optical system 50. If this focusing optical system 46 is a lens having a flat surface, the notch filter 20 may be arranged on this flat surface.

Also, as shown in FIG. 14, a notch filter 20 may be disposed on the light exit surface of the lens that constitutes the collimating optical system 7.

<3> The fluorescent light source device 1 may emit a composite light L1 that is a composite of the blue light L5 from the excitation light source 5 and the fluorescent light L10. In this case, as shown in FIG. 15, the fluorescent light source device 1 may not include a blue light source 9.

Furthermore, as shown in FIG. 16 , the excitation light source 5 may emit excitation light L5 from the back side of the fluorescent plate 10, and a portion of the excitation light L5 transmitted through the fluorescent plate 10 and the fluorescence L10 emitted from the fluorescent plate 10 may be guided to the utilization optical system 50 as a composite light L1.
In this case, from the viewpoint of preventing attenuation of the excitation light L5, it is preferable to use the fluorescent plate 10 in a state where it is not held by the substrate 11, unlike the configuration described above with reference to Fig. 3. Furthermore, the reflective layer 13 is not necessary.

As shown in FIG. 17, excitation light L5 may be incident from the excitation light source 5 obliquely onto the fluorescent plate 10. In this case, a portion of the excitation light L5 reflected by the light incident surface of the fluorescent plate 10 is superimposed on the fluorescent light L10 to obtain a composite light L1.

<4> The structures of the fluorescent light source device 1 shown in Figures 12 to 17 can be combined as appropriate.

<5> The fluorescent plate 10 may include multiple types of fluorescent material 16. Figure 18 is a graph superimposing the spectrum of the synthetic light L1 and the transmission spectrum of the notch filter 20 when the fluorescent material 16 contained in the fluorescent plate 10 is a mixture of LuAG (peak fluorescence wavelength 517 nm) and LSN (peak fluorescence wavelength 556 nm), the binder 17 is alumina, and the blue light source 9 is an LED with a peak wavelength of 455 nm. A filter with the transmission spectrum shown in Figure 2 was used as the notch filter 20.

When the synthetic light L1 obtained at this time was measured using a method conforming to JIS Z 8724, the chromaticity y value was 0.38. Furthermore, when the synthetic light L1 was measured using a method conforming to JIS Z 8726 (method for evaluating the color rendering properties of light sources), an extremely high Ra value of 90.4 was obtained.

As described above with reference to Figures 5 and 6, the y value of the synthetic light L1 is increased compared to when the phosphor 16 is made of a single type of material. This suggests that the fluorescent light source device 1 can generate synthetic light L1 that has a high Ra value while having a low color temperature by providing a fluorescent plate 10 containing multiple types of phosphors 16 that produce fluorescence L10 with different wavelengths.

1: Fluorescent light source device 5: Excitation light source 7: Collimating optical system 9: Blue light source 10: Fluorescent plate 11: Substrate 17: Binder 20: Notch filter 41: Reflecting mirror 43: Dichroic mirror 45: Collimating optical system 46: Condensing optical system 50: Utilizing optical system L1: Synthesized light L10: Fluorescent light L5: Excitation light L9: Blue light

Claims

an excitation light source that emits excitation light in the blue region;
a fluorescent plate that includes a Ce-activated phosphor and receives the excitation light to generate fluorescence having a longer wavelength than the excitation light;
a collimating optical system for reducing at least the divergence angle of the fluorescent light;
a notch filter through which the light emitted from the collimating optical system passes,
the notch filter is disposed such that a light incident surface thereof is oriented substantially perpendicular to an optical axis of a chief ray of light emitted from the collimating optical system;
The cut wavelength range of the notch filter has a center wavelength in the range of 553 nm to 575 nm and a half width in the range of 17 nm to 41 nm;
a notch filter for filtering light emitted from the fluorescent light source and guided to a downstream utilization optical system; a light source device for detecting light emitted from the fluorescent light source and guided to a downstream utilization optical system through the notch filter;
an excitation light source that emits excitation light;
a fluorescent plate including a Ce-activated phosphor and configured to receive the excitation light and generate fluorescence having a longer wavelength than the excitation light;
a collimating optical system for reducing at least the divergence angle of the fluorescent light;
a notch filter through which the light emitted from the collimating optical system passes;
a blue light source that inputs superimposed light of a blue range onto an optical path of the fluorescence emitted from the fluorescent plate,
the notch filter is disposed such that a light incident surface thereof is oriented substantially perpendicular to an optical axis of a chief ray of light emitted from the collimating optical system;
The cut wavelength range of the notch filter has a center wavelength in the range of 553 nm to 575 nm and a half width in the range of 17 nm to 41 nm;
a fluorescent light source device, characterized in that the light guided to a downstream utilization optical system via the notch filter is a composite light of the fluorescent light and light in a blue region, and has an average color rendering index (Ra value) of 85 or more.
The fluorescent light source device according to claim 1 or 2, characterized in that the notch filter has a transmittance of 33% or less for light of the center wavelength of the cut wavelength range.
The fluorescent light source device according to claim 1 or 2, characterized in that the composite light has a chromaticity y in the range of 0.283 to 0.373.
the collimating optical system has a light incidence surface or a light emission surface formed as a flat surface,
3. The fluorescent light source device according to claim 1, wherein the notch filter is disposed on the flat surface.
3. The fluorescent light source device according to claim 1, wherein the fluorescent plate is composed of a binder made of an inorganic material and a sintered body of a Ce-activated oxide phosphor or a Ce-activated nitride phosphor dispersed in the binder.