ULTRAVIOLET IRRADIATION DEVICE

Abstract

An ultraviolet irradiation device includes a light source that emits light showing light intensity in a first wavelength band of 200 nm to 235 nm and a second wavelength band of 240 nm to 280 nm; an optical filter that suppresses the light intensity in the second wavelength band and has transmittance characteristics according to an incident angle of the light emitted from the light source. A first/second angular distribution of light is obtained from a spectrum for each light distribution angle of the light emitted from the optical filter. The first angular distribution of light has a first angle of a light beam showing maximum intensity, the first angle substantially matching with a second angle of a light beam showing maximum intensity in the second angular distribution of light.

Claims

1. An ultraviolet irradiation device comprising: a light source that emits light showing light intensity in a first wavelength band of 200 nm to 235 nm and a second wavelength band of 240 nm to 280 nm and having at least a part of a main emission wavelength band belonging to the first wavelength band; an optical filter that suppresses the light intensity in the second wavelength band and has transmittance characteristics according to an incident angle of the light emitted from the light source, wherein, regarding a first angular distribution of light obtained from a spectrum for each light distribution angle of the light emitted from the optical filter by integrating the light intensity with a wavelength and showing an integrated value for each light distribution angle, the light intensity being in a wavelength band where the main emission wavelength band overlaps the first wavelength band, and regarding a second angular distribution of light obtained from the spectrum for each light distribution angle by integrating the light intensity in the second wavelength band with a wavelength and showing an integrated value for each light distribution angle, the first angular distribution of light has a first angle of a light beam showing maximum intensity, the first angle substantially matching with a second angle of a light beam showing maximum intensity in the second angular distribution of light.

2. The ultraviolet irradiation device according to claim 1, wherein the first angle and the second angle are both between −10 degrees and +10 degrees.

3. The ultraviolet irradiation device according to claim 2, wherein, in the first angular distribution of light, the light intensity of the light beam having a light distribution angle of 40 degrees is smaller than the light intensity of the light beam having the first angle, and the light intensity of the light beam having a light distribution angle of 70 degrees is smaller than the light intensity of the light beam having the light distribution angle of 40 degrees, and in the second angular distribution of light, the light intensity of the light beam having a light distribution angle of 40 degrees is smaller than the light intensity of the light beam having the second angle, and the light intensity of the light beam having a light distribution angle of 70 degrees is smaller than the light intensity of the light beam having the light distribution angle of 40 degrees.

4. The ultraviolet irradiation device according to claim 1, wherein, in a spectrum of light emitted from the optical filter, regarding a first integrated light intensity obtained by integrating the light intensity of a wavelength band in which the main emission wavelength band overlaps the first wavelength band and a second integrated light intensity obtained by integrating the light intensity in the second wavelength band, the second integrated light intensity is 1.0% or less of the first integrated light intensity.

5. The ultraviolet irradiation device according to claim 4, wherein the second integrated light intensity is 0.1% or less of the first integrated light intensity.

6. The ultraviolet irradiation device according to claim 1, wherein the optical filter includes, at a subsequent stage, a diffusion part that diffuses emitted light of the optical filter.

7. The ultraviolet irradiation device according to claim 1, wherein the optical filter has an average transmittance for light in a wavelength band in which the main emission wavelength band overlaps the first wavelength band, the average transmittance showing a decreasing tendency as the incident angle on the optical filter increases from 20 degrees to 60 degrees, and the optical filter has the average transmittance of the optical filter for the light in the second wavelength band, the average transmittance showing an increasing tendency as the incident angle on the optical filter increases from 30 degrees to 60 degrees.

8. The ultraviolet irradiation device according to claim 2, wherein, in a spectrum of light emitted from the optical filter, regarding a first integrated light intensity obtained by integrating the light intensity of a wavelength band in which the main emission wavelength band overlaps the first wavelength band and a second integrated light intensity obtained by integrating the light intensity in the second wavelength band, the second integrated light intensity is 1.0% or less of the first integrated light intensity.

9. The ultraviolet irradiation device according to claim 8, wherein the second integrated light intensity is 0.1% or less of the first integrated light intensity.

10. The ultraviolet irradiation device according to claim 7, wherein the optical filter includes, at a subsequent stage, a diffusion part that diffuses emitted light of the optical filter.

11. The ultraviolet irradiation device according to claim 7, wherein the optical filter has an average transmittance for light in a wavelength band in which the main emission wavelength band overlaps the first wavelength band, the average transmittance showing a decreasing tendency as the incident angle on the optical filter increases from 20 degrees to 60 degrees, and the optical filter has the average transmittance of the optical filter for the light in the second wavelength band, the average transmittance showing an increasing tendency as the incident angle on the optical filter increases from 30 degrees to 60 degrees.

12. The ultraviolet irradiation device according to claim 3, wherein, in a spectrum of light emitted from the optical filter, regarding a first integrated light intensity obtained by integrating the light intensity of a wavelength band in which the main emission wavelength band overlaps the first wavelength band and a second integrated light intensity obtained by integrating the light intensity in the second wavelength band, the second integrated light intensity is 1.0% or less of the first integrated light intensity.

13. The ultraviolet irradiation device according to claim 12, wherein the second integrated light intensity is 0.1% or less of the first integrated light intensity.

14. The ultraviolet irradiation device according to claim 3, wherein the optical filter includes, at a subsequent stage, a diffusion part that diffuses emitted light of the optical filter.

15. The ultraviolet irradiation device according to claim 3, wherein the optical filter has an average transmittance for light in a wavelength band in which the main emission wavelength band overlaps the first wavelength band, the average transmittance showing a decreasing tendency as the incident angle on the optical filter increases from 20 degrees to 60 degrees, and the optical filter has the average transmittance of the optical filter for the light in the second wavelength band, the average transmittance showing an increasing tendency as the incident angle on the optical filter increases from 30 degrees to 60 degrees.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a diagram showing an ultraviolet irradiation device according to an embodiment;

[0044] FIG. 2 is a diagram of the ultraviolet irradiation device in FIG. 1 as viewed from the +Z side;

[0045] FIG. 3 shows an example of a spectrum of ultraviolet light emitted from a light source;

[0046] FIG. 4 is a cross-sectional view of the ultraviolet irradiation device in FIG. 1 as viewed in the X direction;

[0047] FIG. 5A shows an average transmittance of the optical filter when an incident angle of the ultraviolet light is made different;

[0048] FIG. 5B shows an average transmittance of the optical filter when the incident angle of the ultraviolet light is made different;

[0049] FIG. 6 is a diagram for explaining the incident angle of light incident on the optical filter;

[0050] FIG. 7A shows a first angular distribution of emitted light of the ultraviolet irradiation device of the present embodiment;

[0051] FIG. 7B shows a second angular distribution of the emitted light of the ultraviolet irradiation device of the present embodiment;

[0052] FIG. 8 shows a transmission spectrum of an optical filter alone for each incident angle;

[0053] FIG. 9 shows an example of a measurement method of obtaining a transmission spectrum T(λ, θ) for each incident angle;

[0054] FIG. 10 shows a transmission spectrum of the emitted light of the optical filter for each incident angle;

[0055] FIG. 11 shows incident angle characteristics of the optical filter in a second wavelength band;

[0056] FIG. 12 shows an example of a measurement method of obtaining the radiation intensity of the emitted light for each light distribution angle;

[0057] FIG. 13 shows an angular distribution of the emitted light from an ultraviolet irradiation device without an optical filter;

[0058] FIG. 14 shows an angular distribution of light wavelength-integrated with harmful light in the present embodiment;

[0059] FIG. 15 shows an angular distribution of light wavelength-integrated with a part of target light in the present embodiment;

[0060] FIG. 16 shows a modification example of the ultraviolet irradiation device;

[0061] FIG. 17A shows a first angular distribution of light of emitted light of a conventional ultraviolet irradiation device;

[0062] FIG. 17B shows a second angular distribution of light of the emitted light of the conventional ultraviolet irradiation device;

[0063] FIG. 18 is a diagram for explaining a light distribution angle and light intensity;

[0064] FIG. 19 is a perspective view showing a position where the maximum relative irradiance of each of the target light and the harmful light is measured; and

[0065] FIG. 20 is a diagram showing a relationship between an irradiation time and an irradiation dose for each of target light and harmful light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] The drawings are shown using an XYZ coordinate system as appropriate. The specification is described with reference to the XYZ coordinate system as appropriate. In describing directions in the present specification, in the case of distinguishing whether the direction is positive or negative, the positive or negative symbol is added, such as the “+X direction” or the “−X direction”. In the case where there is no need to distinguish between positive and negative directions, the direction is simply described as the “X direction”. Namely, in the present specification, in the case where the direction is simply described as the “X direction”, both “+X direction” and “−X direction” are included. The similar applies to the Y direction and the Z direction.

[Outline of Ultraviolet Irradiation Device]

[0067] An outline of an embodiment of an ultraviolet irradiation device is described with reference to FIG. 1. FIG. 1 is a diagram schematically showing an external appearance of an ultraviolet irradiation device 1 of the embodiment, and FIG. 2 is a drawing of the ultraviolet irradiation device 1 in FIG. 1 as viewed from the +Z side. As shown in FIG. 2, the ultraviolet irradiation device 1 of the present embodiment includes a casing 60 and a light source 30 housed inside the casing 60.

[0068] As shown in FIG. 2, the light source 30 of the present embodiment is an excimer lamp including a plurality of light-emitting tubes 30a and a pair of electrodes 30b. A direction in which the plurality of light-emitting tubes 30a is aligned is defined as an X direction. A direction in which the light-emitting tubes 30a extends is defined as a Y direction. A direction orthogonal to the X direction and the Y direction is a Z direction. As shown in FIG. 4 described later, the plurality of light-emitting tubes 30a are placed on the pair of electrodes 30b. The ultraviolet light emitted from the light-emitting tubes 30a is extracted from a light extraction part 20 to the outside of the casing 60.

[0069] FIG. 3 is a graph showing an example of a spectrum of ultraviolet light L1 emitted from the light source 30. The light source 30 of the present embodiment is an excimer lamp in which krypton (Kr) gas and chlorine (Cl) gas are sealed as light emission gas G1 in the light-emitting tube 30a. When a voltage is applied between the electrodes (30b, 30b), the ultraviolet light L1 having a wavelength showing the maximum intensity of 222 nm as shown in FIG. 3 is emitted. A wavelength at 222 nm, which is the wavelength showing the maximum intensity, is in a first wavelength band (200 nm to 235 nm).

[0070] The ultraviolet light emitted from the light source 30 exhibits a spectrum that has a main emission wavelength band MB between 216 nm or more and 223 nm or less. The main emission wavelength band MB is a wavelength band showing light intensity of 10% or more of the maximum intensity in the light source 30.

[0071] As shown in FIG. 3, the light source 30 emits light in a second wavelength band of 240 nm to 280 nm although the emission intensity thereof is very low. Because the light in the second wavelength band is the harmful light, the light in the second wavelength band is restricted by an optical filter to be described later, and the harmful light is prevented from leaking out of the casing 60 of the ultraviolet irradiation device 1.

[0072] In the present embodiment, the excimer lamp in which Kr gas and Cl gas are sealed is employed as the light source 30, but the present invention is not limited thereto. An excimer lamp filled with another gas (for example, an excimer lamp filled with Kr gas and Br gas and having the maximum intensity in the vicinity of 207 nm) may be adopted as the light source 30. In addition, a solid state light source such as a light-emitting diode (LED) may be adopted as the light source 30.

[0073] In the case of the excimer lamp in which Kr gas and Cl gas are sealed, the entire main emission wavelength band MB belongs to the first wavelength band of 200 nm to 235 nm. However, the entire main emission wavelength band MB may not be located in the first wavelength band. At least a part of the main emission wavelength band MB may belong to the first wavelength band. The light source 30 in which at least a part of the main emission wavelength band belongs to the first wavelength band includes, for example, a light source in which the upper limit of the main emission wavelength band MB exceeds 235 nm. Examples of the light source having the upper limit of the main emission wavelength band MB exceeding 235 nm include solid state light sources such as LEDs.

[0074] FIG. 4 is a cross-sectional view of the ultraviolet irradiation device 1 in FIG. 1 as viewed in the X direction. An optical axis Lc of the ultraviolet light L1 emitted from the ultraviolet irradiation device 1 is shown together with an arrow indicating an emission direction. The optical axis Lc extends along the Z direction. An optical filter 40 is disposed in the light extraction part 20. The ultraviolet irradiation device 1 emits only light that has passed through the optical filter 40 among ultraviolet light having a spectrum as shown in FIG. 3.

[0075] In a case where the light source 30 is an excimer lamp extending in one direction (Y direction in this example) as shown in FIGS. 2 and 4, the light distribution angle of the emitted light flux appearing on a plane (for example, YZ plane) including the extending direction may be different from the light distribution angle of the emitted light flux appearing on a plane (for example, XZ plane) orthogonal to the extending direction. In the present specification, in a case where the light intensity for each light distribution angle is expressed as an angular distribution of light, for the sake of convenience, the “angular distribution of light” is defined by using an arithmetic mean value of the light intensity for each light distribution angle appearing in a plane including the extending direction and for the light intensity for each light distribution angle appearing in a plane orthogonal to the extending direction.

[Optical Filter]

[0076] The optical filter 40 mainly transmits light in the first wavelength band (200 nm to 235 nm) and mainly reflects light belonging to the second wavelength band (240 nm to 280 nm). The optical filter 40 of the present embodiment transmits the entire main emission wavelength band MB. However, the optical filter 40 only needs to transmit at least a part of the main emission wavelength band MB.

[0077] For a spectrum of light transmitted through the optical filter 40 and emitted from the ultraviolet irradiation device 1, a value obtained by integrating light intensity with a wavelength is referred to as a first integrated light intensity, wherein the light intensity is integrated in the first wavelength band overlapping the main emission wavelength band MB and the first wavelength band (200 nm to 235 nm). In the present embodiment in which the entire main emission wavelength band MB (216 nm or more and 223 nm or less) is in the first wavelength band, a value obtained by integrating the light intensity of the main emission wavelength band MB with a wavelength corresponds to the first integrated light intensity. A value obtained by integrating light intensity in the entire second wavelength band (240 nm to 280 nm) with a wavelength is referred to as a second integrated light intensity.

[0078] When the maximum value (for example, in a case where the emission angle of the optical filter 40 is 0°) of the first integrated light intensity is compared with the second integrated light intensity, the second integrated light intensity is very small with respect to the maximum value of the first integrated light intensity. Specifically, the second integrated light intensity is 3% or less, more preferably 2% or less, and still more preferably 1% or less to the maximum value of the first integrated light intensity.

[0079] The optical filter 40 includes a dielectric multilayer film formed on a base material. Examples of the dielectric multilayer film include a dielectric multilayer film in which hafnium oxide (HfO.sub.2) layers and silicon dioxide (SiO.sub.2) layers are alternately laminated, and a dielectric multilayer film in which SiO.sub.2 layers and aluminum oxide (Al.sub.2O.sub.3) layers are alternately laminated. The dielectric multilayer film in which the HfO.sub.2 layers and the SiO.sub.2 layers are alternately laminated can reduce the number of layers for obtaining the same wavelength-selective characteristics as compared with the dielectric multilayer film in which the SiO.sub.2 layers and the Al.sub.2O.sub.3 layers are alternately laminated, and thus can increase the transmittance of the selected ultraviolet light.

[0080] A base material of the optical filter 40 is made of material that can transmit ultraviolet light included in the first wavelength band of 200 nm to 235 nm. As the specific material for the base material, the following can be adopted which is a ceramic-based material such as silica glass, borosilicate glass, sapphire, magnesium fluoride material, calcium fluoride material, lithium fluoride material, and barium fluoride material, or a resin-based material such as a silicon resin and a fluororesin.

[0081] The transmittance of the ultraviolet light transmitted through the optical filter 40 changes depending on an incident angle θ incident on the optical filter 40 and a wavelength band range of the ultraviolet light to be transmitted. As shown in FIG. 6, the incident angle θ is an angle formed between a light beam L3 incident on the optical filter 40 and a normal line N1 of an incident surface 40s of the optical filter 40 on which the light beam L3 is incident.

[0082] As an evaluation method of transmittance characteristics of the optical filter 40, there is a method of obtaining and using an average transmittance in a specific wavelength band according to the incident angle. The average transmittance in a specific wavelength band is obtained from a transmission spectrum T(λ, θ) for each incident angle of the optical filter 40. A method of obtaining the transmission spectrum T(λ, θ) for each incident angle is described later.

[0083] FIGS. 5A and 5B show results of obtaining the transmittance characteristics of the optical filter 40 by the above-described evaluation method. FIG. 5A shows incident angle characteristics of the average transmittance in the main emission wavelength band MB (in the present embodiment, 216 nm or more and 223 nm or less) that is transmitted through the optical filter 40. In the graph in FIG. 5A, the horizontal axis represents the incident angle θ at which the light of the main emission wavelength band MB is incident on the optical filter 40, and the vertical axis represents the average transmittance of the main emission wavelength band MB. The transmittance is represented by a relative value in which the transmittance is 1 when an incident angle of light of the main emission wavelength band MB is 0 degrees.

[0084] FIG. 5B shows incident angle characteristics of the average transmittance of the harmful light (240 nm to 280 nm) transmitted through the optical filter 40. Although by much smaller amount than the amount of the target light, the optical filter 40 transmits the harmful light. In the graph in FIG. 5B, the horizontal axis represents the incident angle θ at which the harmful light is incident on the optical filter 40, and the vertical axis represents the average transmittance of the harmful light. The transmittance is expressed as a relative value in which the transmittance is 1 when an incident angle of the harmful light is 0 degrees.

[0085] From FIGS. 5A and 5B, the average transmittance of the target light tends to decrease as the incident angle θ on the optical filter 40 increases from 20 degrees to 60 degrees. In contrast to the transmission characteristics of the target light, the average transmittance of the harmful light tends to increase as the incident angle θ on the optical filter 40 increases from 30 degrees to 60 degrees. As shown in FIGS. 17A and 17B, the difference in the transmission characteristics with respect to the incident angle θ caused by the difference in the wavelength band becomes a factor that the angular distribution of the light intensity is different between the target light and the harmful light.

[Light Angular Distribution of Target Light/Harmful Light]

[0086] FIG. 7A is an angular distribution of target light emitted from the ultraviolet irradiation device 1 of the present embodiment. More specifically, the angular distribution of light is a diagram obtained from a spectrum for each light distribution angle of the light emitted from the optical filter 40 by integrating light intensity of a wavelength band with a wavelength and showing the integrated light intensity for each light distribution angle, the wavelength band including the main emission wavelength band MB that overlaps the first wavelength band. This is referred to as a first angular distribution of light. In the case of the present embodiment in which the entire main emission wavelength band MB (216 nm or more and 223 nm or less) is in the first wavelength band, the first angular distribution of light is a diagram obtained by integrating the light intensity of the main emission wavelength band MB with a wavelength and showing the integrated light intensity for each light distribution angle.

[0087] FIG. 7B is an angular distribution of the harmful light emitted from the ultraviolet irradiation device 1 of the present embodiment. More specifically, this is an angular distribution of light obtained from a spectrum for each light distribution angle of light emitted from the optical filter 40 by integrating light intensity in the second wavelength band (240 nm to 280 nm) with a wavelength for each light distribution angle. This is referred to as a second angular distribution of light. The first angular distribution of light and the second angular distribution of light are obtained by a method described later.

[0088] In each of the first angular distribution of light and the second angular distribution of light, the horizontal axis represents the light distribution angle (deg.), and the vertical axis represents the light intensity I(θ). Note that it should be understood that the light distribution angle (deg.) and the light intensity I(θ) are similarly defined as in FIGS. 17A and 17B, which are described with reference to FIGS. 18 and 19.

[0089] From the first angular distribution of light in FIG. 7A, it can be seen that the light distribution angle of the light beam indicating the maximum intensity of the target light is 0 degrees. From FIG. 7B, it can be seen that the light distribution angle of the light beam indicating the maximum intensity of the harmful light is 0 degrees. That is, both the maximum intensity of the target light and the maximum intensity of the harmful light appear on the optical axis Lc of the light emitted from the ultraviolet irradiation device 1. Therefore, when the irradiation dose D according to the relaxation of the TLV is set, the irradiation dose D of both the target light and the harmful light can be monitored with the spectroscope or the optical sensor by only measuring the light intensity (relative irradiance) at the position of the optical axis Lc on the irradiated surface.

[0090] As both the light distribution angle (first angle) of the light beam indicating the maximum intensity in the first angular distribution of light and the light distribution angle (second angle) of the light beam indicating the maximum intensity in the second angular distribution of light become closer to 0 degrees, the positions (P1, P2) where the light intensity is monitored can be set in the vicinity of the optical axis Lc of the emitted light. As a result, the adjustment of the ultraviolet irradiation device 1 according to the relaxation of the TLV becomes simple.

[0091] According to FIG. 7A, as the absolute value of the light distribution angle gradually increases from the first angle (in the example in FIG. 7A, near 0 degrees), 40 degrees, and to 70 degrees, the light intensities of the target light and the harmful light decrease. According to FIG. 7B, as the absolute value of the light distribution angle gradually increases from the second angle (in the example in FIG. 7B, near 0 degrees), 40 degrees, and to 70 degrees, the light intensities of the target light and the harmful light decrease. This leads to the fact that there is no problem even when a light beam having a light distribution angle of 40 degrees or 70 degrees is emitted as long as the light intensities at the first angle and the second angle are considered at the time of determining the irradiation dose D according to the relaxation of the TLV. Therefore, the adjustment of the ultraviolet irradiation device according to the relaxation of the TLV becomes simple.

[0092] Further, according to FIGS. 7A and 7B, as the absolute value of the light distribution angle increases from the first angle or the second angle to 30 degrees, the light intensities of the target light and the harmful light gradually decrease. This leads to the fact that there is no problem in the irradiated surface irradiated with a light beam having a light distribution angle of ±30 degrees from the first angle (second angle) as long as the light intensity at the first angle or the second angle is considered at the time of determining the irradiation dose D according to the relaxation of the TLV. Therefore, the adjustment of the ultraviolet irradiation device according to the relaxation of the TLV becomes simple.

[Method of Matching Second Angle with First Angle]

[0093] As shown in FIGS. 7A and 7B, regarding the emitted light emitted from the optical filter 40, the second angle indicating the maximum value of the integrated light intensity in the second angular distribution of light obtained by integrating with a wavelength of the second wavelength band is substantially matched with the first angle indicating the maximum value of the integrated light intensity in the first angular distribution of light obtained by integrating the light intensity of the main emission wavelength band. Therefore, there are roughly two methods, which are: (I) a method of adjusting the incident angle incident on the optical filter 40; and (II) a method of using the optical filter 40 having appropriate transmittance characteristics according to the incident angle. The first angle and the second angle can be substantially matched with each other by at least one of the method (I) and the method (II).

[0094] The method (I) of adjusting the incident angle incident on the optical filter 40 is described. When the light distribution angle of the emitted light from the light source 30 is small, the target light is easily transmitted and the harmful light is not easily transmitted. In the light source 30, for example, the absolute value of the light distribution angle that is a half value of the maximum intensity of the emitted light is preferably within 60 degrees, and more preferably within 40 degrees.

[0095] An example of a method of adjusting the light distribution angle of the light source 30 is described. For example, in a case where the surfaces of the pair of electrodes 30b function as reflecting surfaces of emitted light from the light-emitting tubes 30a, the incident angle incident on the optical filter 40 can be adjusted by adjusting the shape of each of the electrodes 30b.

[0096] The incident angle at which the emitted light from the light source 30 is incident on the optical filter 40 may be adjusted by arranging a transmission optical system such as a lens between the light source 30 and the optical filter 40. In addition, the incident angle incident on the optical filter 40 may be adjusted by changing the shape of the light source 30 itself.

[0097] In the method (II) of using the optical filter 40 having appropriate transmittance characteristics, in the optical filter 40, the transmittance characteristics according to the incident angle change when a composition, a layer thickness, the number of laminated layers, and the like of the dielectric multilayer film change. An intrinsic angular distribution of light is determined by the transmittance characteristics according to the incident angle. Therefore, by obtaining the angular distribution of light, the optical filter 40 having desired transmittance characteristics according to the incident angle is designed or selected.

[Method of Obtaining Angular Distribution of Light]

[0098] An example of a method of obtaining the angular distribution of light is described. The angular distribution of light of the optical filter 40 can be obtained by performing the following steps (a) to (e). As described above, after the angular distribution of light is obtained, the first angle of the light beam indicating the maximum value of the integrated light intensity in the first angular distribution of light is compared with the second angle of the light beam indicating the maximum value of the integrated light intensity in the second angular distribution of light. Then, depending on whether the difference between the first angle and the second angle is small or not, the transmittance characteristics according to the incident angle of the optical filter 40 is determined to be appropriate or not.

(a) Measurement of a Spectrum of Light Emitted from the Light Source 30

[0099] Light intensity I(λ) emitted from the light source 30 is measured using a spectroscope to obtain a spectrum. In this measurement, for example, the emitted light from the ultraviolet irradiation device 1 may be measured in a state where the optical filter 40 is removed from the ultraviolet irradiation device 1. The wavelength to be measured is in a wavelength range (in the present embodiment, a range from 200 nm to 280 nm) including the target light and the harmful light. The measurement result is shown as, for example, a graph in which the wavelength (nm) is plotted on the horizontal axis and the relative intensity with the intensity of the wavelength showing the maximum intensity as 100% is plotted on the vertical axis as shown in FIG. 3.

(b) Measurement of a Transmission Spectrum of the Optical Filter 40 for Each Incident Angle

[0100] The optical filter 40 to be a candidate is prepared, and the transmission spectrum T(λ, θ) of the optical filter 40 alone for each incident angle is obtained. For example, as shown in FIG. 8, the transmission spectrum T(λ, θ) for each incident angle is shown as a graph in which the wavelength (nm) is plotted on the horizontal axis and the transmittance (%) is plotted on the vertical axis. FIG. 8 shows a total of three transmission spectra T(λ, θ) when the incident angle θ of the optical filter 40 is 0 degrees, 20 degrees, and 40 degrees.

[0101] FIG. 9 shows an example of a measurement method of obtaining the transmission spectrum T(λ, θ) for each incident angle. The optical filter 40 inclined at a predetermined incident angle θ with respect to the normal line N1 of the optical filter 40 is arranged. Then, directional light L2 is made incident on the optical filter 40 from a center Q1 of the light source 30. The light intensity of the light transmitted through the optical filter 40 is measured by a spectroscope 50. By removing light intensity of the emitted light in a case where there is no optical filter from the measured light intensity, the transmission spectrum T(λ) of the optical filter 40 is obtained. Then, the transmission spectrum T(λ, θ) is obtained by performing measurement while changing the incident angle θ by inclining the optical filter 40 with respect to the traveling direction of the light L2.

[0102] FIG. 8 only shows a total of three transmission spectra T(λ, θ) of the incident angles at 20 degree intervals, which are 0 degrees, 20 degrees, and 40 degrees. However, the interval for obtaining the transmission spectrum T(λ, θ) may be narrowed. For example, the measurement may be performed while changing the incident angle by 5 degrees between 0 to 70 degrees to obtain a total of 15 transmission spectra T(λ, θ) having different incident angles θ.

(c) Calculation of the Transmission Spectrum of the Emitted Light of the Optical Filter for Each Incident Angle

[0103] By multiplying the light intensity I(λ) obtained in (a) by the transmission spectrum T(λ, θ) of the optical filter 40 obtained in (b), light intensity I.sub.FO(λ, θ) of the emitted light transmitted through the optical filter 40 for each incident angle is obtained. That is, the light intensity I.sub.FO(λ, θ) of the light emitted from the optical filter 40 for each incident angle is expressed by the following formula (1).

[Formula 1]

I.sub.FO(λ, θ)=I(λ)×T(λ, θ)  (1)

[0104] In FIG. 10, the spectrum of the light intensity I.sub.FO(λ, θ) emitted from the optical filter 40 is shown for each incident angle (as an example, three types of incident angles are shown, which are 0 degrees, 20 degrees, and 40 degrees) incident on the optical filter 40.

(d) Calculation of Integrated Intensity of the Harmful Light

[0105] By using the light intensity I.sub.FO(λ, θ) of the emitted light obtained in (c), integrated intensity S.sub.B2(θ) of the second wavelength band (240 to 280 nm) indicating the harmful light is obtained. The integrated intensity S.sub.B2(θ) of the second wavelength band is expressed by the following formula (2).

[00001]$\left[\mathrm{Formula}2\right]$$\begin{array}{cc}\begin{array}{c}{S}_{B2}\left(\theta \right)={\int }_{240}^{280}{I}_{\mathrm{FO}}\left(\lambda ,\theta \right)d\lambda \\ ={\int }_{240}^{280}I\left(\lambda \right)\times T\left(\lambda ,\theta \right)d\lambda \end{array}& \left(2\right)\end{array}$

[0106] FIG. 11 shows incident angle characteristics of the optical filter 40 in the second wavelength band. By obtaining the integrated intensity S.sub.B2(θ) of the second wavelength band for the incident angle of 0 to 70 degrees, for example, a graph in which the incident angle θ to the optical filter 40 is plotted on the horizontal axis and the integrated intensity (relative value) of the second wavelength band is plotted on the vertical axis as in FIG. 11 is obtained. As can be seen from the graph of FIG. 11, the integrated intensity S.sub.B2(θ) of the second wavelength band increases as the absolute value of the incident angle θ on the optical filter 40 increases.

(e) Calculation of an Angular Distribution of the Emitted Light from an Ultraviolet Irradiation Device Without the Optical Filter 40

[0107] An angular distribution of the light emitted from an ultraviolet irradiation device 10 without the optical filter 40 is obtained by the following procedure. First, for example, as shown in FIG. 12, while the spectroscope 50 is rotationally moved about the center Q1 of the light source 30 so as to draw a circle around the Y-axis direction, the radiation intensity of the emitted light is measured by the spectroscope 50. As a result, relative radiation intensity E(θ) for each light distribution angle of the ultraviolet irradiation device 10 can be obtained. Then, from the relative radiation intensity E(θ), the light intensity I(θ) of the emitted light from the ultraviolet irradiation device 10 on the irradiated plane can be obtained (see FIG. 1). The light intensity I(θ) is obtained by the following formula (3).

[Formula 3]

I(θ)=E(θ)×(cos θ).sup.3  (3)

[0108] For example, as shown in FIG. 13, the light intensity I(θ) of the emitted light from the ultraviolet irradiation device 10 without the optical filter 40 is indicated as the angular distribution of light in which the incident angle (light distribution angle) θ to the optical filter 40 is plotted on the horizontal axis and the relative value of the light intensity in a case where the light intensity at θ=0 is 1 is plotted on the vertical axis.

[0109] By multiplying the light intensity I(θ) by the integrated intensity S.sub.B2(θ) in the second wavelength band, a second angular distribution I.sub.B2(θ) that is a light intensity distribution according to the light distribution angle of the harmful light emitted from the ultraviolet irradiation device 1 is obtained. That is, the second angular distribution I.sub.B2(θ) of the harmful light is obtained by the following formula (4).

[00002]$\left[\mathrm{Formula}4\right]$$\begin{array}{cc}\begin{array}{c}{I}_{B2}\left(\theta \right)=I\left(\theta \right)\times S_{B2}\left(\theta \right)\\ =E\left(\theta \right)\times {\left(\cos \theta \right)}^3\times {\int }_{240}^{280}I\left(\lambda \right)\times T\left(\lambda ,\theta \right)d\lambda \end{array}& \left(4\right)\end{array}$

[0110] FIG. 14 shows the second angular distribution I.sub.B2(θ) in which the light distribution angle (deg.) is plotted on the horizontal axis, and the relative value of light intensity obtained by integrating the wavelength in a range of 240 nm to 280 nm is plotted on the vertical axis.

[0111] The method of obtaining the angular distribution of light has been described above by taking the harmful light as an example. A first angular distribution I.sub.B1(θ) of the target light can be obtained by the similar method as described above. FIG. 15 shows the first light distribution angle distribution I.sub.B1(θ) in which the light distribution angle (deg.) is plotted on the horizontal axis and the integrated intensity of the target light is plotted on the vertical axis.

[0112] Comparison between the second angular distribution I.sub.B2(θ) in FIG. 14 and the first angular distribution I.sub.B1(θ) in FIG. 15 shows that the difference is small between the first angle of the light beam indicating the maximum value of the integrated light intensity in the first angular distribution of light and the second angle of the light beam indicating the maximum value of the integrated light intensity in the second angular distribution of light, and that the optical filter 40 has appropriate transmittance characteristics for the ultraviolet irradiation device.

[0113] The embodiment of the ultraviolet irradiation device has been described above. However, the present invention is not limited to the above embodiment, and various changes or modifications may be made to the above embodiment without departing from the spirit of the present invention.

[0114] As an improvement example, as shown in FIG. 16, a diffusion part 70 that diffuses the emitted light of the optical filter 40 may be provided at a subsequent stage of the optical filter 40. This makes it possible to spread the ultraviolet light over a wide range in a suitable state. In a case where the diffusion part 70 is provided, the effect obtained by the present invention is more remarkable.

[0115] More specifically, in the conventional ultraviolet irradiation device shown in FIGS. 17A and 17B, the position P1 irradiated with the light beam indicating the maximum intensity of the target light differs greatly from the position P2 irradiated with the light beam indicating the maximum intensity of the harmful light (see FIG. 19). Therefore, in a case of using the ratio of the harmful light to the target light at the position P1 as a reference, when the emitted light from the optical filter 40 is diffused by the diffusion part 70, the ratio of the harmful light included in the diffused light is averaged to cause the ratio of the harmful light to be easily increased more than the reference. In addition, the degree of the increase rate is also difficult to be predicted.

[0116] On the other hand, in the present invention, as described above, both the light distribution angle (first angle) of the light beam indicating the maximum intensity in the first light distribution angle distribution and the light distribution angle (second angle) of the light beam indicating the maximum intensity in the second angular distribution of light become closer to 0 degrees. That is, the position P1 irradiated with the light beam indicating the maximum intensity of the target light becomes close to the position P2 irradiated with the light beam indicating the maximum intensity of the harmful light. Therefore, when the emitted light from the optical filter 40 is diffused by the diffusion part 70, the ratio of the harmful light included in the diffused light maintains the reference or is reduced to be lower than the reference. Therefore, management in terms of safety is easier, and the ultraviolet light can be spread in a wide range in a more preferable state. The diffusion part 70 is, for example, a plate-like or film-like optical member.

[0117] The optical filter 40 may be disposed in the vicinity of the light source 30 instead of being disposed in the light extraction part 20. In addition, the optical filter 40 may be disposed as a part of the light source 30, for example, in a sealing body of the lamp.