Dome-shaped illumination device and measurement device

Abstract

To provide a dome type illumination device and a measuring device capable of obtaining an angular illumination distribution close to Lambert's cosine law at an opening of a dome type housing.SOLUTION: The dome-shaped lighting device 1 includes a dome-shaped casing 11 having a diffusive reflecting surface 13 on an inner surface thereof and having an opening 15 through which illumination light diffused by the diffusive reflecting surface 13 is emitted, and one or more light sources 12 arranged along an inner periphery of the dome-shaped casing 11 and configured to emit light such that a main illumination angle A1 is directed toward a vertex of the dome-shaped casing 11 with respect to a normal direction A2 of the opening 15.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dome-shaped illumination device used in a color measurement device or the like, and to a measurement device such as a color measurement device that uses this dome-shaped illumination device. [Background technology]

[0002] For example, a d:8 spectral colorimeter calculates color values ​​from the reflectance (spectral distribution) of an illuminated object, and in order to accurately measure the reflectance characteristics of the object, it is necessary to illuminate the object surface with the same luminous flux from each angle of incidence. In other words, the ideal illumination is one with an angular illumination distribution that follows Lambert's cosine law. An approximation would be a white LED with a flat light-emitting surface, and in a spectral colorimeter, illumination that is close to Lambert's cosine law is obtained by using an integrating sphere with a Lambertian diffusion surface.

[0003] However, in dome-shaped lighting devices used in machine vision and in-line measurement, it is not possible to obtain angular illumination close to Lambert's cosine law at the dome opening due to the influence of the light distribution and arrangement of the light source, and baffles such as light-shielding walls.

[0004] As an example of a conventional dome-shaped illumination device, Patent Document 1 discloses a color inspection device and a color inspection method that use a dome-shaped illumination device in its illumination system. This dome-shaped illumination device includes a dome-shaped housing with a diffuse reflection surface on its inner surface and an opening through which illumination light diffused by the diffuse reflection surface is emitted, and multiple light sources arranged in a ring shape within the dome-shaped housing. Each light source is arranged so that the main illumination angle is in the normal direction of the opening of the dome housing.

[0005] Patent Document 2 also discloses an illumination device that includes multiple light sources arranged in a ring shape so that the main irradiation angle of the light is in the normal direction of the opening, a reflecting section formed of an ellipsoid, and an opening that emits illumination light diffused by the reflecting surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-194449 [Patent Document 2] Japanese Patent Application Publication No. 2017-133984 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the illumination devices described in Patent Documents 1 and 2, the main illumination angle of the light sources arranged in a ring is directed in the normal direction of the aperture surface, which poses a problem in that an angular illumination distribution close to Lambert's cosine law cannot be obtained at the aperture.

[0008] This invention has been made to solve these problems, and aims to provide a dome-shaped lighting device and a measurement device that can obtain an angular illumination distribution close to Lambert's cosine law at the opening of the dome-shaped housing. [Means for solving the problem]

[0009] The above object can be achieved by the following means. (1) a dome-shaped housing having a diffuse reflection surface on its inner surface and an opening through which illumination light diffused by the diffuse reflection surface exits; one or more light sources arranged along an inner periphery of the dome-shaped housing, emitting light with a main irradiation angle directed toward an apex of the dome-shaped housing rather than a normal direction of the opening; A dome-shaped lighting device comprising: (2) The dome-shaped lighting device according to the preceding paragraph 1, wherein the plurality of light sources are discretely arranged along the entire or part of the inner periphery of the dome-shaped housing. (3) The dome-shaped lighting device according to the preceding paragraph 1, wherein the light source is a Lambertian light distribution light source. (4) The dome-shaped lighting device according to the above item 1, wherein the angular intensity distribution of the illumination light at the opening varies from Lambert's cosine law by −4% to +4%. (5) The dome-shaped lighting device according to the above paragraph 1, wherein the light source has a half-power angle of 37 degrees to 83 degrees. (6) The dome-shaped lighting device according to any one of the preceding paragraphs 1 to 5, wherein the main irradiation angle of the light source is 5 degrees or more from the normal direction of the opening and points toward the apex of the dome-shaped housing. (7) The dome-shaped lighting device according to any one of the preceding paragraphs 1 to 5, wherein the main irradiation angle of the light source is 25 degrees or more from the normal direction of the opening and points toward the apex of the dome-shaped housing. (8) A dome-shaped lighting device according to any one of the preceding paragraphs 1 to 5; a light receiving means for receiving reflected light of light emitted from the dome-shaped lighting device onto a measurement object placed in an opening of the dome-shaped lighting device; A measuring device comprising: (9) The measuring device according to the preceding paragraph 8, wherein the plurality of light sources in the dome-shaped lighting device are discretely arranged along all or part of the inner circumference of the dome-shaped housing. (10) The measuring device according to the preceding paragraph 8, wherein the light source in the dome-shaped lighting device is a Lambertian light distribution light source. (11) The measurement device according to the preceding paragraph 8, wherein the variation in the angular intensity distribution of the illumination light at the opening in the dome-shaped illumination device is −4% to +4%. (12) The measuring device according to the preceding paragraph 8, wherein the light source in the dome-shaped lighting device has a half-power angle of 37 degrees to 83 degrees. (13) The measuring device according to any one of paragraphs 8 to 12, wherein the main irradiation angle of the light source in the dome-shaped lighting device is directed toward the apex of the dome-shaped housing by 5 degrees or more from the normal direction of the opening. (14) The measuring device according to any one of paragraphs 8 to 12, wherein the main irradiation angle of the light source in the dome-shaped lighting device is directed toward the apex of the dome-shaped housing at an angle of 25 degrees or more from the normal direction of the opening. [Effects of the Invention]

[0010] According to the dome-shaped lighting device of the present invention, one or more light sources are arranged along the inner periphery of a dome-shaped housing having a diffuse-reflecting surface on its inner surface and an opening through which the illumination light diffused by the diffuse-reflecting surface is emitted. The light sources emit light with a main illumination angle toward the apex of the dome-shaped housing, rather than toward the normal to the opening. Therefore, compared to when light is emitted toward the normal to the opening, the distance between the light source and the diffuse-reflecting surface is longer, and the amount of light corresponding to the light source's luminous intensity distribution is proportional to the distance from the light source to the diffuse-reflecting surface. Because illuminance is determined by the light source orientation distribution and the square law of the distance, the illuminance seen from each light source becomes more uniform, and the amount of light irradiated from the diffuse-reflecting surface to the opening also becomes more uniform. In other words, the opening can achieve uniform illuminance and an angular illumination distribution close to Lambert's cosine law.

[0011] According to the measuring device of this invention, the opening of the dome-shaped lighting device provides uniform illuminance and an angular illumination distribution close to Lambert's cosine law, and the light reflected from the object to be measured placed at this opening is received by the light receiving means, so that the reflection characteristics of the object to be measured can be measured with high accuracy. [Brief explanation of the drawings]

[0012] [Figure 1] 1A is a perspective view showing a dome-shaped lighting device according to an embodiment of the present invention with a part cut away, FIG. 1B is a plan view of the same, and FIG. 1C is a longitudinal sectional view of the same. [Figure 2] 10A and 10B are diagrams illustrating angular illumination distributions of openings in a conventional dome-shaped illumination device and in the dome-shaped illumination device according to the present embodiment. [Figure 3] FIG. 1A shows the light distribution of a Lambertian distribution light source and a light source with a half-power angle of 37 degrees in this embodiment, and FIG. 1B shows the angular illumination distribution of the opening of a dome-shaped lighting device according to the prior art and this embodiment, both of which use a light source with a half-power angle of 37 degrees. [Figure 4]10A and 10B show the results of a simulation of the change in the angular illumination intensity distribution at the opening when the half-value angle of the light source is changed using the dome-shaped illumination device according to this embodiment, where (A) shows the luminous intensity distribution of the light source at each half-value angle, and (B) shows the angular illumination intensity distribution at the opening for each light source at each half-value angle. [Figure 5] 10 is a table showing the allowable half-value angle when the dome diameter Φ1 is 150 mm. [Figure 6] (A) shows the angular illumination distribution of the aperture when a simulation was performed by changing the direction of the main irradiation angle A1 of each light source, and (B) shows the amount of change from the ideal (Lambert's cosine law). [Figure 7] 1A and 1B are diagrams schematically illustrating the hemispherical dome-shaped housing of the present embodiment and a conventional integrating sphere for comparison. [Figure 8] (A) shows the illumination angle distribution of the opening when a conventional dome-shaped lighting device is operated with the main illumination angle of the light source facing the normal direction of the opening while changing the distance between the opening and the object to be measured, and (B) shows the illumination angle distribution of the opening of the dome-shaped lighting device of this embodiment. [Figure 9] FIG. 2 is a diagram schematically illustrating a spectrophotometer using the dome-shaped illumination device shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] FIG. 1(A) is a perspective view showing a dome-shaped lighting device 1 according to an embodiment of the present invention, with a part cut away, (B) is a plan view of the same, and (C) is a longitudinal cross-sectional view of the same.

[0015] The dome-shaped lighting device 1 includes a dome-shaped housing 11 with an open bottom and a plurality of light sources 12 .

[0016] The dome-shaped housing 11 has a hemispherical shell shape that is circular in plan view and semicircular in front view, and has a hemispherical diffuse reflection surface 13 on its inner surface. It also has a ring-shaped light source mounting portion 14 that protrudes horizontally by a predetermined width from the bottom peripheral edge of the dome-shaped housing 11 in the direction of the central axis, and has a circular opening 15 on the inside of the light source mounting portion 14.

[0017] At a position on the inner peripheral surface side of the dome-shaped housing 11 in the light source mounting portion 14, a plurality of light sources 12 are arranged in a ring shape and discretely at equal intervals along the entire inner circumference of the bottom end of the dome-shaped housing 11. Each light source 12 is an LED light source, and is mounted on the light source mounting portion 14 so that the main irradiation angle A1 of each light source 12 is such that the light is emitted toward the vertex P of the dome-shaped housing rather than the normal direction A2 of the opening 15, as shown in FIG.

[0018] The light sources 12 may be arranged discretely at equal intervals in an arc shape along part of the inner periphery of the lower end of the dome-shaped housing 11, rather than along the entirety of the inner periphery. Also, a single continuous ring-shaped or arc-shaped light source may be arranged along the entirety or part of the inner periphery of the lower end of the dome-shaped housing.

[0019] In this way, by each light source 12 emitting light at its main irradiation angle A1 toward the vertex P of the dome-shaped housing 11, uniform illuminance and an angular illumination distribution close to Lambert's cosine law can be obtained at the opening 15.

[0020] That is, Because a Lambertian distribution light source has the strongest amount of light in the main irradiation direction, if light is emitted at main irradiation angle A1 toward normal direction A2 of opening 15 as in the conventional case, reflected light will be generated from the diffuse reflection surface at the intersection position and will be directly irradiated onto opening 15. As a result, even in dome-shaped housing 11 with a completely uniform diffusing surface, the amount of light reflected at a specific angle from the diffuse reflection surface at the intersection position will be high due to the influence of the light directly reflected onto opening 15, resulting in a distribution that deviates from Lambert's cosine law.

[0021] In contrast, in this embodiment, light emitted from each light source 12 toward vertex P of dome-shaped housing 11 is diffusely reflected by diffuse reflecting surface 13 on the inner surface of dome-shaped housing 11 and irradiated onto opening 15. By directing main irradiation angle A1 of light source 12 toward dome vertex P, where the distance between light source 12 and diffuse reflecting surface 13 is the longest, the amount of light corresponding to the luminous intensity distribution of light source 12 and the distance from light source 12 to diffuse reflecting surface 13 are proportional to each other. Since illuminance is determined by the orientation distribution of light source 12 and the square law of the distance, the illuminance seen from each light source 12 is uniform, and the amount of light irradiated from diffuse reflecting surface 13 onto opening 15 is also uniform. In other words, uniform illuminance and an angular illumination distribution close to Lambert's cosine law are obtained at opening 15.

[0022] FIG. 2 illustrates the angular illumination distribution of the opening 15 in a conventional dome-shaped illumination device and in the dome-shaped illumination device 1 according to this embodiment. In the conventional dome illumination device, the main illumination angle A1 of each light source 12 is in the normal direction A2 of the opening 15, while in the dome-shaped illumination device 1 according to this embodiment, the main illumination angle A1 of each light source 12 is in the direction of the vertex P of the dome-shaped housing 11. The ideal Lambert's cosine law (cos characteristic) is also shown. The horizontal axis of FIG. 2 represents the angle, and the vertical axis represents the relative intensity (au) when the relative illumination intensity of the Lambert's cosine law is 100%.

[0023] As shown in FIG. 2, it can be seen that the dome lighting device 1 according to this embodiment is closer to the ideal Lambert's cosine law.

[0024] The light source 12 used in this embodiment is preferably a Lambertian light distribution light source with a half-power angle of 60 degrees, but it does not have to be a Lambertian light distribution light source.

[0025] 3(A) and 3(B) show simulation results for a conventional dome lighting device and the dome-shaped lighting device 1 of this embodiment when the half-value angle of light source 12 is changed. In the simulation, the dome diameter Φ1 (see FIG. 1(C)), which is the maximum inner diameter of dome-shaped housing 11 excluding light source mounting portion 14, was set to 150 mm, and the opening diameter Φ2, which is the diameter of opening 15, was set to 110 mm, and multiple light sources 12 made of LEDs were discretely arranged at equal intervals in a ring shape. In the conventional dome lighting device, the main irradiation angle A1 of each light source 12 was set to the normal direction A2 of opening 15, while in the dome-shaped lighting device 1 of this embodiment, the main irradiation angle A1 of each light source 12 was set to the direction of vertex P of dome-shaped housing 11.

[0026] 3A shows the light distribution of the Lambertian distribution light source 12 of this embodiment and the light source 12 with a half-power angle of 37 degrees, while FIG. 3B shows the angular illumination distribution of the opening 15 of the conventional dome-shaped lighting device 1 of this embodiment and the dome-shaped lighting device 1 using a light source with a half-power angle of 37 degrees. Note that FIG. 3B also shows the ideal Lambert's cosine law (cos characteristic).

[0027] From the results of the angular illumination distribution of opening 15 in FIG. 3(B), it can be seen that even if the half-value angle of light source 12 differs from the half-value angle of a Lambertian distribution light source, directing main illumination direction A1 of light source 12 toward dome apex P as in this embodiment is closer to the ideal Lambert's cosine law (cos characteristic) than directing it toward normal direction A2 of opening 15 as in the conventional case.

[0028] In this case, how close it is to Lambert's cosine law depends on the half-value angle and dome diameter Φ1 of the light source 12. The closer the half-value angle of the light source 12 is to a Lambertian light distribution light source and the larger the dome diameter Φ1, the closer it is to Lambert's cosine law.

[0029] 4 shows the results of a simulation of the change d in the angular illumination intensity distribution at the opening 15 when the half-power angle of the light source 12 is changed using the dome-shaped illumination device 1 according to this embodiment, with the dome diameter Φ1 set to 150 mm and the opening diameter Φ2 set to 110 mm. The change d is the amount of change when the relative angular illumination intensity distribution at the opening 15 follows Lambert's cosine law, with 0% as the change, and is calculated using the following formula: In the formula, I is the relative angular illumination intensity when the illumination intensity distribution follows Lambert's cosine law, and I' is the relative angular illumination intensity for a certain half-power angle light source.

[0030]

number

[0031] FIG. 4A shows the light distribution of the light source 12 at each half-value angle, and FIG. 4B shows the angular illumination intensity distribution of the opening 15 for each light source 12 at each half-value angle.

[0032] If we define that a variation d of ±4% or less is equivalent to Lambert's cosine law, then when the dome diameter Φ1 is 150 mm and the opening diameter Φ2 is 110 mm, an angle of 60°±23° is equivalent to Lambert's cosine law. In other words, light source 12 does not have to be a Lambertian light distribution light source, but it is desirable that it be a light source having a half-power angle of 37 degrees to 83 degrees.

[0033] The allowable half-value angle when the dome diameter Φ1 is 150 mm is shown in the table in Figure 5. In the conventional example, a large change rate of 7.0% occurs when the half-value angle is 37 degrees.

[0034] As described above, by emitting light at the main irradiation angle A1 from each light source 12 toward the vertex P of the dome-shaped housing 11, uniform illuminance and an angular illumination distribution close to Lambert's cosine law can be obtained at the opening 15, but the direction of the main irradiation angle A1 of the light source 12 may not be strictly toward the vertex P, but may be toward the peripheral area of ​​the vertex P. However, in this embodiment, it is not limited to each light source 12 emitting light at the main irradiation angle A1 toward the vertex P of the dome-shaped housing 11 or its peripheral area, and it is sufficient that the main irradiation angle A1 of the light source 12 is oriented toward the vertex P of the dome-shaped housing 11 with respect to the normal direction A2 of the opening 15.

[0035] Because the main illumination angle A1 is directed toward the vertex P of the dome-shaped housing 11 rather than the normal direction A2 of the opening 15, the distance between the light source 12 and the diffuse reflection surface 13 is longer than when the main illumination angle A1 is directed toward the normal direction A2 of the opening 15, and therefore the opening 15 is closer to Lambert's cosine law.

[0036] Using a dome-shaped housing 11 with a dome diameter Φ1 of 150 mm and an aperture diameter Φ2 of 110 mm, a simulation was performed in which the direction of the main illumination angle A1 of each light source 12 was changed from the normal direction A2 of the aperture 15 to various angles θ (see FIG. 1C): 0 degrees, 10 degrees, 25 degrees, and vertex direction. The angular illumination distribution of the aperture 15 is shown in FIG. 6(A). Also, FIG. 6(B) shows the amount of change from the ideal (Lambert's cosine law) for θ: 0 degrees, 5 degrees, 10 degrees, 25 degrees, and vertex direction. Note that θ: 0 means that the main illumination angle A1 is oriented in the normal direction A2 of the aperture 15, as in the conventional case.

[0037] From the results of Figures 6(A) and (B), it is clear that the effect is observed when the main irradiation angle A1 of the light source 12 is oriented toward the apex P of the dome-shaped housing 11 at an angle θ of 5 degrees or more from the normal direction A2 of the opening 15, and more preferably, the main irradiation angle A1 of the light source 12 is oriented toward the apex P of the dome-shaped housing 11 at an angle θ of 25 degrees or more from the normal direction A2 of the opening 15.

[0038] 1 illustrates the dome-shaped housing 11 having a hemispherical shell shape that is circular in plan view and semicircular in front view, but the height dimension of the dome-shaped housing 11 is not limited to that shown in the figure. The height dimension may be equal to or less than half the dome diameter Φ1, or may be equal to or more than half.

[0039] Furthermore, the shape of the dome-shaped housing 11 in a plan view may not be circular but may be elliptical or other shapes, and the shape in a front view may not be semicircular but may be semielliptical or other shapes.

[0040] However, when the hemispherical dome-shaped housing 11 of this embodiment is used, the illumination system has the same effect as a conventional integrating sphere type illumination system, but is about half the size, so miniaturization can be expected.

[0041] 7A and 7B are schematic diagrams comparing the hemispherical dome-shaped housing 11 of the present embodiment with a conventional integrating sphere 20. In the same figure, (A) shows the dome-shaped housing 11, and (B) shows the integrating sphere 20. Comparing (A) and (B) reveals that the dome-shaped housing 11 can be made significantly smaller than the integrating sphere 20.

[0042] Furthermore, as shown in the comparison diagrams at the top of Figures (A) and (B), while the illumination device has the same effect as a conventional integrating sphere type illumination device, the aperture diameter Φ2 of aperture 15 can be made larger, which increases the range (shown by the dashed line in Figure 7) over which the reflection characteristics of measurement object 30 can be obtained, and a wider measurement range can be expected. The larger the aperture diameter Φ2, the lower the error sensitivity due to fluctuations in the height of measurement object 30, making the measurement device more resistant to height fluctuations.

[0043] The angular illuminance distribution is determined by the aperture diameter Φ2 and the solid angle at the center of the object to be measured 30; the larger the aperture diameter Φ2, the larger the solid angle; and the larger the aperture diameter Φ2, the smaller the fluctuation in solid angle when the height changes, so there is little change in the light intensity and angular illuminance distribution.

[0044] For the same reason, as shown in the comparison diagram at the bottom of Figures 7(A) and (B), if non-contact measurement is performed by increasing the distance between each opening 15, 21 and the object to be measured 30, this can also contribute to extending the distance of non-contact measurement.

[0045] 8(A) and (B) show the results of investigating the illumination angle distribution of opening 15 for a conventional dome-shaped illumination device in which the main illumination angle A1 of light source 12 is directed toward the normal direction A2 of opening 15, and for dome-shaped illumination device 1 according to this embodiment in which the main illumination angle A1 of light source 12 is directed toward the vertex P of dome-shaped housing 11, while the distance between opening 15 and measurement object 30 is changed to 0 mm, 5 mm, 10 mm, 15 mm, and 20 mm. Fig. 8(A) shows the conventional dome-shaped illumination device, and Fig. 8(B) shows the dome-shaped illumination device 1 according to this embodiment.

[0046] 7(A) and 7(B), it can be seen that the dome-shaped illumination device 1 according to this embodiment has smaller waveform disturbances at each distance and smaller errors when the working distance fluctuates.

[0047] Figure 9 shows a schematic diagram of a spectrophotometer (corresponding to a measuring device) 40 using the dome-shaped lighting device shown in Figure 1, where (A) is a perspective view with a portion cut away, and (B) is a longitudinal cross-sectional view.

[0048] This spectrophotometer 40 is equipped with a camera (corresponding to a light receiving means) 41 mounted on a partial wall surface of the dome-shaped housing 11 facing the internal space of the dome-shaped housing 11. Then, color measurement is performed by placing a measurement object 30 in the opening 15 of the dome-shaped lighting device 1. Light emitted from the light source 12 of the dome-shaped lighting device 1 at a main irradiation angle A1 toward the vertex P of the dome-shaped housing 11 relative to the normal direction A2 of the opening 15 is diffused by the diffuse reflection surface 13 on the inner surface of the dome-shaped housing 11 and illuminates the measurement object 30. The reflected light of this illumination light from the measurement object 30 is received by the camera 41 and calculated by a calculation unit (not shown) to obtain a measurement value.

[0049] As mentioned above, the opening 15 of the dome-shaped lighting device 1 has uniform illuminance and an angular illumination distribution close to Lambert's cosine law. Therefore, the reflected light from the measurement object 30 placed at this opening 15 is received by the camera 41, and the reflection characteristics of the measurement object 30 can be measured with high accuracy. [Industrial Applicability]

[0050] The present invention can be used as an illumination device for a color measurement device or the like. [Explanation of symbols]

[0051] 1 Dome-shaped lighting device 11 Dome-shaped housing 12 light source 13 Diffuse Reflection Surface 14 Light source mounting part 15 Opening 30 Measurement object 40 Spectrophotometer (measuring device) 41 Camera (light receiving means)

Claims

1. a dome-shaped housing having a diffuse reflection surface on its inner surface and an opening through which illumination light diffused by the diffuse reflection surface exits; one or more light sources arranged along an inner periphery of the dome-shaped housing, emitting light with a main irradiation angle directed toward an apex of the dome-shaped housing rather than a normal direction of the opening; A dome-shaped lighting device comprising:

2. 2. The dome-shaped lighting device according to claim 1, wherein the plurality of light sources are discretely arranged along the entire or part of the inner periphery of the dome-shaped housing.

3. 2. The dome lighting device according to claim 1, wherein the light source is a Lambertian light source.

4. 2. The dome-shaped lighting device according to claim 1, wherein the angular intensity distribution of the illumination light at the opening varies from Lambert's cosine law by −4% to +4%.

5. 2. The dome lighting device according to claim 1, wherein the light source has a half-power angle of 37 degrees to 83 degrees.

6. 6. The dome-shaped lighting device according to claim 1, wherein the main irradiation angle of the light source is oriented toward the apex of the dome-shaped housing by 5 degrees or more from the normal direction of the opening.

7. 6. The dome-shaped lighting device according to claim 1, wherein the main illumination angle of the light source is 25 degrees or more from the normal direction of the opening toward the apex of the dome-shaped housing.

8. A dome-shaped lighting device according to any one of claims 1 to 5; a light receiving means for receiving reflected light of light emitted from the dome-shaped lighting device onto a measurement object placed in an opening of the dome-shaped lighting device; A measuring device comprising:

9. 9. The measuring device according to claim 8, wherein the plurality of light sources in the dome-shaped lighting device are discretely arranged along the entire or part of the inner periphery of the dome-shaped housing.

10. 9. The measuring device according to claim 8, wherein the light source in the dome-shaped lighting device is a Lambertian light distribution light source.

11. 9. The measuring device according to claim 8, wherein the amount of change in the angular intensity distribution of the illumination light at the opening in the dome-shaped illumination device is −4% to +4%.

12. 9. The measuring device according to claim 8, wherein the light source in the dome-shaped lighting device has a half-power angle of 37 degrees to 83 degrees.

13. 13. The measuring device according to claim 8, wherein a main irradiation angle of the light source of the dome-shaped lighting device is directed toward the apex of the dome-shaped housing by 5 degrees or more from the normal direction of the opening.

14. 13. The measuring device according to claim 8, wherein a main irradiation angle of the light source of the dome-shaped lighting device is directed toward the apex of the dome-shaped housing by 25 degrees or more from the normal direction of the opening.

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