A diffuse illumination and diffuse reception measurement method for reflectance spectrum of structural color materials

Abstract

The present invention provides a diffuse illumination diffuse reception measurement method for the reflection spectrum of a structural color material, which adopts diffuse reflection illumination diffuse reflection reception (d:d) measurement geometric conditions, and mainly includes an illumination light source, a collimator, an integrating sphere, a spectrometer and a computer. There are three openings in the integrating sphere, and the positions of the three openings are designed to ensure that a light shield is added to prevent light from being directly transmitted between the openings. Among them, the sample light hole (3b) is respectively clamped with a standard white board, a black board and a sample to be measured, and their spectral signal data V are respectively measured. w (λ), V d (λ), V s (λ), and then calculate the object spectral reflectance ρ(λ) according to formula (1), and calculate the CIELab value according to (2) and (3). The reflectance spectrum of the structural color material can be accurately and stably measured with a single measurement.

Description

Technical Field

[0001] The invention relates to the technical field of structural color materials, and in particular to a diffuse illumination and diffuse reception measurement method for a reflection spectrum of a structural color material. Background Art

[0002] Structural colors are various colors produced by the reflection, refraction, scattering, diffraction or interference of light and the microstructure of materials, which have the characteristics of changing color with angle. Structural color materials have the advantages of high brightness, high saturation, never fading, iridescent effect, etc., and are widely used in the fields of security information expression and material surface treatment. Currently, commonly used structural color materials include holographic anti-counterfeiting materials with diffraction color change characteristics, pearlescent paint with interference color change characteristics, and glitter paint with high metallic luster.

[0003] The angular discoloration characteristics of structural color materials make it difficult to accurately measure the reflectance spectrum and color of their surface coatings. In the printing industry, the human eye cannot directly visually evaluate the color difference of the ink on the surface of holographic laser paper, and can only cover the surface with translucent materials and then visually detect the color change. However, while this method reduces the impact of the diffraction color change effect on visual evaluation, it also covers up other quality problems of the sample. Similarly, in the automobile manufacturing industry, due to the angular discoloration characteristics of metallic pearlescent paint and glitter paint, it is difficult for the human eye to judge the defects of the car body coating.

[0004] Laser paper commonly used in the printing industry is a kind of structural color material. Its structure is as follows Figure 1 As shown in the figure, layer A is the ink layer, layer B is the protective layer, layer C is the grating layer, layer D is the aluminum-plated layer, and layer E is the base paper. The grating layer of laser paper will diffract the incident light, thus producing an effect of changing color with angle, making it difficult to measure and control the spectrum and color of the ink layer.

[0005] In response to the above issues:

[0006] Reference [1] (CN200710066196.4) proposes a film and detection method for detecting laser paper. First, snowflake ink is printed on a blank film to make a laser paper detection film, which is then covered on the surface of the laser paper and its surface spectrum and color data are detected using a spectrophotometer.

[0007] References [2] (CN 211696677 U), [3] (CN 105841818 A) and [4] are to install a d / 8° geometry colorimetric instrument on a platform that can move and rotate along the XY axis, and to represent the ink layer spectrum or color by measuring multiple angles at a fixed point or measuring multiple points along different axes and taking the average value.

[0008] References [5] (CN 113324654A) and [6] (CN 113324653 A) developed color measurement devices that use dual light sources or rod-shaped light sources to identify the position information of the straight line where the dark light column of the cylindrical laser paper is located, and then use a d / 8° geometric condition colorimeter to measure the color data on the dark light column.

[0009] Reference [7](CN201010578507.7) discloses a spectrophotometer based on a dual integrating sphere structure for measuring the color of laser paper. The integrating sphere is used to illuminate the sample with diffuse light, and the integrating sphere is used to collect the reflected light of the sample to measure the color.

[0010] Pearlescent paint is a commonly used topcoat material for automobiles, furniture, plastics and other products. Its common structure is as follows: Figure 2 As shown in the figure, layer A is the varnish layer, layer B is the pearlescent paint layer, and layer C is the base paint layer (natural paint). The pearlescent layer contains pearl mica pigments, which have a pearl-like luster. Since pearls are translucent or transparent, light can reach the base paint layer, so the color of the three-coat pearlescent paint is a mixture of the colors reflected by the pearl mica and the base paint layer, which is deeply loved by people.

[0011] Affected by the interference or specular reflection of the pearlescent paint layer, the color and effect of the paint surface change with the change of the illumination angle and the observation angle. The existing spectrophotometers with d / 8° geometry and 45 / 0 geometry cannot accurately measure the automotive topcoat. The method disclosed in document [8] (CN 210427337 U) is to measure the sample at multiple angles through the illumination light path and the observation light path, obtain 12 sets of measurement data of the color and effect of the automotive topcoat under different illumination angles and observation angles, and form an evaluation report on the color and effect of the automotive topcoat.

[0012] Compared with directly measuring the laser paper, measuring the surface color of the laser paper after covering it with sulfuric acid transfer paper can improve the consistency of the measurement results. However, the covering sulfuric acid transfer paper will affect the measurement results, resulting in the measurement value being unable to accurately express the surface color of the laser material.

[0013] The methods used in references [2], [3], [4], and [8] are multi-angle or multi-position measurements. This method can improve the consistency and accuracy of reflectance spectrum and color measurement, and may basically accurately reflect the surface coating information of structural color materials. However, this method requires multiple measurements, and the selection of measurement angles and positions will affect the consistency of the measurement results. In addition, the measurement efficiency is low and is not suitable for continuous, rapid, and online detection requirements in modern production process control.

[0014] The method disclosed in references [5] and [6] is to use a dual light source or a rod-shaped light source to identify the location of the dark light column of the columnar laser paper, and then use a colorimeter to measure the color. This method improves the measurement accuracy by avoiding the diffraction of the laser paper grating layer, but this method can only be used to measure columnar laser paper, and is not suitable for other types of laser paper and structural color materials. In addition, the measurement process and steps are complicated and cannot meet actual production needs.

[0015] The double integrating sphere spectrophotometer method published in reference [7] can accurately express the surface color of diffraction color-changing materials, but it has the disadvantages of complex optical path structure and high cost.

[0016] The above measurement methods mostly use 8-degree directional geometric conditions (d:8° or 8°:d geometric conditions, such as Figure 3 There is also a case of using a double integrating sphere to achieve diffuse illumination and diffuse absorption as described in the literature [7], but its optical path structure is complex and the measurement accuracy is not high. The multi-angle measurement method cannot avoid the problem of high reflection of the sample surface at some angles because the measurement angle is fixed, and the measurement equipment is expensive. Summary of the invention

[0017] The purpose of the present invention is to provide a diffuse illumination diffuse reception measurement method for the reflection spectrum of a structural color material, so as to solve the technical problems that the reflection spectrum and color of the surface coating of the structural color material cannot be accurately measured, and the measurement cost and measurement efficiency of the prior art are high.

[0018] To achieve the above-mentioned purpose, the present invention provides a diffuse illumination diffuse reception measurement system for a reflection spectrum of a structural color material, the main component of which is an integrating sphere (3), the x-axis, y-axis and z-axis of a three-dimensional coordinate system are constructed with the center of the integrating sphere (3) as the origin, holes are opened at the intersections of the negative direction of the x-axis, the negative direction of the y-axis, the positive direction of the z-axis and the integrating sphere (3), which serve as an incident light hole (3a), a sample light hole (3b) and a detection light hole (3c), respectively; an illumination light source (1) is arranged outside the integrating sphere (3) in the negative direction of the x-axis, the detection light hole (3c) is connected to a spectrometer (4) via an optical fiber, and the spectrometer collects spectrum signals and communicates with a computer (5).

[0019] Preferably, the source of the structural color material includes but is not limited to: laser paper, car paint.

[0020] Preferably, a collimator (2) is arranged between the illumination light source (1) and the integrating sphere (3), and the incident light hole (3a) is coupled to the collimator and connected to the illumination light source to ensure that the light from the light source is collimated to illuminate the incident light hole (3a).

[0021] Preferably, the sample light hole (3b) is coupled to a reflective sample holder, and is used to clamp a standard white board, or a standard black board / light trap, or a sample to be tested.

[0022] Preferably, the detection light hole (3c) is coupled to an optical fiber connector for connecting to a spectrometer.

[0023] The present invention also provides a diffuse illumination diffuse reception measurement method for the reflectance spectrum of a structural color material based on the above system, wherein the measurement geometric condition d:d is that the illumination light source first emits incident light, which is collimated through an incident light hole (3a) to illuminate the wall of an integrating sphere, and then diffused by the integrating sphere to illuminate a sample placed in a sample light hole (3b). The reflected light of the sample is diffused by the integrating sphere and then received by an optical fiber at a detection light hole (3c) to enter a spectrometer (4). The spectrometer (4) then collects a spectral signal, and finally a computer (5) processes the spectral signal to obtain spectral signal data V w (λ), V d (λ), V s (λ) and color data.

[0024] Preferably, the spectral signal data is obtained by the following method:

[0025] (A) The spectral reflectance is ρ w A standard white plate with a wavelength of (λ) is placed at the sample light hole (3b), and a spectrometer is used to measure its spectral signal data V w (λ);

[0026] (B) The spectral reflectance is ρ d A standard blackboard or light trap with a wavelength of (λ) is placed at the sample light hole (3b), and a spectrometer is used to measure its spectral signal data V d (λ);

[0027] (C) Place the sample to be tested at the sample light hole (3b) and use a spectrometer to measure its spectral signal data V s (λ).

[0028] Preferably, the color data is obtained by the following method:

[0029] (a) Calculate the spectral reflectance ρ of the sample to be tested using formula (1) s (λ);

[0030]

[0031] (b) According to the basic principle of colorimetry, the tristimulus values ​​of the surface color of the object are calculated using formula (2);

[0032]

[0033] In formula (2), k is the normalization coefficient, ρ s (λ) is the spectral reflectance of the sample to be tested, S(λ) is the relative spectral power distribution of the standard illuminant specified by CIE, It is the standard chromaticity observer data specified by CIE, and XYZ is the tristimulus value of the surface color of the object;

[0034] (c) According to the basic principle of colorimetry, the Lab value of the surface color of the object is calculated using formula (3);

[0035]

[0036] In formula (3), X, Y, and Z are the three stimulus values ​​of the object being measured. n ,Y n ,Z n It is the tristimulus value of the standard illuminant.

[0037] The present invention has the following beneficial effects:

[0038] The present invention adopts diffuse reflection illumination diffuse reflection reception (d:d) measurement geometric conditions, mainly including an illumination light source, a collimator, an integrating sphere, a spectrometer and a computer. There are three openings in the integrating sphere, and the positions of the three openings are designed to ensure that a light shield is added to prevent light from directly transmitting between the openings. Among them, the sample light hole (3b) is respectively clamped with a standard whiteboard, a blackboard and a sample to be tested, and their spectral signal data V are respectively measured. w (λ), V d (λ), V s (λ), and then calculate the object spectral reflectance ρ(λ) according to formula (1), and calculate the CIELab value according to (2) and (3). The reflectance spectrum of the structural color material can be accurately and stably measured with a single measurement.

[0039] The present invention discloses a full diffuse reflection reflection spectrum and color measurement method, which realizes diffuse illumination and diffuse reception measurement of the reflection spectrum of the surface of a structural color material, ensures that the reflection spectrum and color of the sampling point do not change with the change of the measurement angle, and the repetitive accuracy of measuring the reflection spectrum and color of the surface coating of the structural color material is better than that of the existing measurement method, thereby meeting the color detection and control requirements of the surface coating of the structural color material.

[0040] The present invention adopts a single integrating sphere structure to realize diffuse illumination and diffuse reception of the surface of the structural color material, eliminates the influence of the light-changing effect of the surface of the structural color material on the reflection spectrum and color measurement, and realizes accurate and stable measurement of the reflection spectrum and color of the surface of the structural color material. The measurement accuracy and stability are better than the existing technology.

[0041] The present invention adopts a single integrating sphere, a fiber optic light source and a fiber optic spectrometer to form a measuring system, does not need a special moving mechanism to switch the measuring angle, has a simple structure, stable measurement and low cost.

[0042] The measuring method of the present invention is simple and convenient, only requires a single measurement, and does not need to measure multiple times at the same position to obtain an average value. The measuring method has a fast measuring speed and high working efficiency, and can meet the requirements of both off-line and on-line measurements.

[0043] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0045] Figure 1 This is a multi-layer structure diagram of laser paper;

[0046] Figure 2 This is a multi-layer structure diagram of pearlescent paint;

[0047] Figure 3 It is the 8-degree directional reflection measurement geometric condition, where A is the d:8° geometric condition and B is the 8°:d geometric condition;

[0048] Figure 4 The measurement geometry is for diffuse illumination diffuse reception (d:d);

[0049] Figure 5 A diffuse receiving measurement system for the surface spectrum diffuse illumination of structural color materials;

[0050] Figure 6 Schematic diagram of measurement at different angles. DETAILED DESCRIPTION

[0051] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0052] The present invention mainly realizes the diffuse illumination and diffuse reception measurement geometry (d:d geometry) in the reflection measurement geometry recommended by CIE 15:2004, such as Figure 4 shown.

[0053] like Figure 5As shown, a diffuse illumination diffuse reception measurement system for the reflection spectrum of a structural color material is provided, wherein the main component is an integrating sphere 3, and the x-axis, y-axis and z-axis of a three-dimensional coordinate system are constructed with the center of the integrating sphere 3 as the origin, and holes are opened at the intersections of the negative direction of the x-axis, the negative direction of the y-axis, and the positive direction of the z-axis with the integrating sphere 3, which serve as an incident light hole 3a, a sample light hole 3b, and a detection light hole 3c, respectively; an illumination light source 1 is arranged outside the integrating sphere 3 in the negative direction of the x-axis, and the detection light hole 3c is connected to a spectrometer 4 through an optical fiber, and the spectrometer collects spectral signals and communicates with a computer 5.

[0054] A collimator 2 is arranged between the illumination light source 1 and the integrating sphere 3, and the incident light hole 3a is coupled to the collimator and connected to the illumination light source to ensure that the light from the light source is collimated to illuminate the incident light hole 3a.

[0055] The sample light hole 3b is coupled to a reflective sample holder and is used to clamp a standard white board, or a standard black board / light trap, or a sample to be tested.

[0056] The detection light hole 3c is coupled to an optical fiber connector for connecting to a spectrometer.

[0057] A diffuse illumination and diffuse reception measurement method for the reflectance spectrum of a structural color material based on the above system is as follows: first, the illumination light source emits incident light, which is collimated through the incident light hole 3a to illuminate the wall of the integrating sphere, and then diffused by the integrating sphere to illuminate the sample placed in the sample light hole 3b. The sample reflected light is diffused by the integrating sphere and then received by the optical fiber at the detection light hole 3c to enter the spectrometer 4, and then the spectrometer 4 collects the spectral signal. Finally, the computer 5 processes the spectral signal to obtain the spectral signal data V w (λ), V d (λ), V s (λ) and color data.

[0058] The specific method for obtaining spectral signal data and color data is as follows:

[0059] Step 1: Transform the spectral reflectance into ρ w The standard white plate with a wavelength of (λ) is placed at the sample light hole 3b, and the spectral signal data V is measured by a spectrometer. w (λ);

[0060] Step 2: Transform the spectral reflectance into ρ d A standard blackboard or light trap with a wavelength of (λ) is placed at the sample light hole 3b, and a spectrometer is used to measure its spectral signal data V d (λ);

[0061] Step 3: Place the sample to be tested at the sample aperture 3b and use a spectrometer to measure its spectral signal data V s (λ);

[0062] Step 4: Calculate the spectral reflectance ρ of the sample to be tested using formula (1) s (λ);

[0063]

[0064] Step 5: According to the basic principle of colorimetry, use formula (2) to calculate the tristimulus values ​​of the object surface color;

[0065]

[0066] In formula (2), k is the normalization coefficient. ρ s (λ) is the spectral reflectance of the sample to be tested, S(λ) is the relative spectral power distribution of the standard illuminant specified by CIE, It is the standard chromaticity observer data specified by CIE, and XYZ is the tristimulus value of the surface color of the object;

[0067] Step 6: According to the basic principle of colorimetry, use formula (3) to calculate the Lab value of the surface color of the object;

[0068]

[0069] In formula (3), X, Y, and Z are the three stimulus values ​​of the object being measured. n ,Y n ,Z n It is the tristimulus value of the standard illuminant.

[0070] In order to compare with the measurement methods in related literature, the method of the present invention is used for data verification. The implementation steps are as follows:

[0071] Build as Figure 5 The spectral and color measurement platform shown.

[0072] Place the standard white plate at the sample light hole 3b and use the spectrometer with an integration time t ref Measure its spectral signal data V r (λ).

[0073] The standard blackboard is placed at the sample light hole 3b, and the spectrometer is used with an integration time t ref Measure its spectral signal data V d (λ).

[0074] Place the laser beam paper at the sample aperture 3b and use a spectrometer with an integration time t ref Get the same position 0 degree position (such as Figure 6 The spectral signal data V 0° (λ).

[0075] In order to compare with the methods described in references [2] and [4] and to express the measurement accuracy and stability of this method at different measurement angles, further measurements were performed by rotating the sample angle to compare with the relevant literature data.

[0076] Keep the measurement position unchanged, rotate the sample angle, and use the spectrometer with integration time t ref Get the spectral signal data V at other angles at the same position 45° (λ), V 90° (λ), V 135° (λ), V 180° (λ), V 225° (λ), V 270° (λ), V 315° (λ).

[0077] According to the spectral signal data, the spectral reflectance ρ of the same position measured at different angles is calculated using formula (1) 0° (λ),ρ 45° (λ),ρ 90° (λ),ρ 135° (λ),ρ 180° (λ),ρ 225° (λ),ρ 270° (λ),ρ 315° (λ).

[0078] According to the spectral reflectance at different angles at the same position, the tristimulus values ​​XYZ at different angles at the same position are calculated using formula (2).

[0079] According to the tristimulus values ​​at different angles at the same position, the Lab values ​​at different angles at the same position are calculated using formula (3).

[0080] Table 1 shows the Lab values ​​of beam laser base paper, plain laser base paper, starry sky laser base paper, floral laser base paper, and beam laser prints at the same position and different angles measured by the above method.

[0081] The maximum color difference calculation method in Table 1 is the same as the method used in the patent, that is, randomly select the Lab value of any angle from 0 to 360 as the standard value, and calculate the CIELAB color difference with the chromaticity values ​​of other angles from 0 to 360 at the same measurement position, as shown in formula (4), and record the maximum color difference ΔE * ab .

[0082]

[0083] In the formula and is the CIELAB value of a certain angle set as a standard value, and are the CIELAB values ​​for other angles.

[0084] The mean square color difference MCDM in Table 1 is the same as the method used in the literature and is calculated using formula (5).

[0085]

[0086] In the formula and is the CIELAB value measured at the ith angle, and It is the average value of CIELAB values ​​at 8 measurement angles. The mean square color difference is the color difference between each measurement value and the average measurement value. The average value of .

[0087] Table 1 Data of laser paper samples measured by the method of the present invention

[0088]

[0089] By comparing the measurement data in Table 1 and the reference [2], it can be seen that the maximum color difference (0.98) of the laser beam paper measured by the present invention is smaller than the maximum color difference (1.11) of the method three used in the reference [2], and the maximum color difference (0.62) of the laser beam print measured by the present invention is smaller than the maximum color difference (1.12) of the method three used in the reference [2].

[0090] Comparing Table 1 with the data in the reference, it can be seen that the MCDM (0.1) of the starry sky pattern laser paper measured by the present invention is smaller than the MCDM (0.36) of the method used in the reference [4]. The MCDM (0.08) of the floral pattern laser paper measured by the present invention is smaller than the MCDM (0.49) of the method used in the reference [4]. According to Table 1, the MCDM (0.24) of the beam laser paper measured by the present invention is smaller than the MCDM (0.93) of the method used in the reference [4]. The MCDM (0.21) of the beam laser print measured by the present invention is smaller than the MCDM (0.54) of the method used in the reference [4].

[0091] The present invention can be used not only for measuring laser paper, but also for other structural color materials with special structures such as automobile topcoat.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0093]

References

[0094] [1] Zhou Daoming. A film and detection method for detecting laser paper:, CN101131536A[P]. 2008.

[0095] [2] Huang Min, Li Zeyang, Shi Chunjie, et al. A color measurement device for laser beam paper and printed products, CN206056780U[P], 2017.

[0096] [3] Huang Min, et al. A device for accurate color measurement and color difference evaluation of laser paper and printed matter, CN211696677U[P], 2020.

[0097] [4]Xinguo Huang, XiaoxiaWan, Zhen Liu. Optimization of the method for color measurement of printing onholographic paper [J]. ColorResearch&Application, 2013, 38(2): 130–138.

[0098] [5] Li Junfeng, Wei Chunao. Laser paper color detection device based on automatic dark light column positioning of rod-shaped light source, CN113324654A[P], 2021.

[0099] [6] Li Junfeng, Wei Chunao. Double-light source columnar laser paper color detection device based on diamond diffraction pattern, CN113324653A[P], 2021.

[0100] [7] Sun Peng, Xiao Chao, Wan Xiaoxia, et al. Spectrophotometer for colorimetric detection of laser paper, CN102538970B[P]. 2014.

[0101] [8] Su Chaoyang, Fei Weigang, Wang Xin. A measuring device for automotive topcoat, CN210427337U[P].2020.

Claims

1. A diffuse illumination diffuse reception measurement method for the reflection spectrum of structural color materials, It is characterized in that The main component of the diffuse illumination diffuse reception measurement system for implementing the method is an integrating sphere (3). The x-axis, y-axis and z-axis of a three-dimensional coordinate system are constructed with the center of the integrating sphere (3) as the origin. Holes are opened at the intersection of the negative direction of the x-axis, the negative direction of the y-axis and the positive direction of the z-axis with the integrating sphere (3), which serve as an incident light hole (3a), a sample light hole (3b) and a detection light hole (3c), respectively. An illumination light source (1) is arranged outside the integrating sphere (3) in the negative direction of the x-axis. The detection light hole (3c) is connected to a spectrometer (4) via an optical fiber. The spectrometer collects spectral signals and communicates with a computer (5). Structural color materials include: laser paper or car paint; The sample light hole (3b) is coupled to a reflective sample holder and is used to clamp a standard white board, a standard black board, a light trap, or a sample to be tested; The detection light hole (3c) is coupled to an optical fiber connector for connecting to a spectrometer; The specific method is as follows: The measurement geometric condition is d:d. First, the illumination light source emits incident light, which is collimated through the incident light hole (3a) to illuminate the wall of the integrating sphere. After being diffused by the integrating sphere, the incident light illuminates the sample placed in the sample light hole (3b). The reflected light of the sample is diffused by the integrating sphere and then received by the detection light hole (3c) through the optical fiber into the spectrometer (4). The spectrometer (4) then collects the spectral signal. Finally, the computer (5) processes the spectral signal to obtain the spectral signal data. , , and color data; The spectral signal data is obtained by the following method: (A) The spectral reflectance is A standard white plate is placed at the sample light hole (3b), and its spectral signal data is measured using a spectrometer. ; (B) The spectral reflectance is A standard blackboard or light trap is placed at the sample light hole (3b), and its spectral signal data is measured using a spectrometer. ; (C) Place the sample to be tested at the sample light hole (3b) and use a spectrometer to measure its spectral signal data. ; Color data is obtained by: (a) Calculate the spectral reflectance of the sample to be tested using formula (1): ; (1) (b) According to the basic principle of colorimetry, the tristimulus values ​​of the surface color of the object are calculated using formula (2); (2) In formula (2), k is the normalization coefficient, , is the spectral reflectance of the sample to be tested, The relative spectral power distribution of the standard illuminant specified by CIE. , , It is the standard chromaticity observer data specified by CIE, and XYZ is the tristimulus value of the surface color of the object; (c) According to the basic principle of colorimetry, the Lab value of the surface color of the object is calculated using formula (3); (3) In formula (3), is the tristimulus value of the object being measured, It is the tristimulus value of the standard illuminant.

2. The method according to claim 1, It is characterized in that A collimator (2) is arranged between the illumination light source (1) and the integrating sphere (3), and the incident light hole (3a) is coupled to the collimator and connected to the illumination light source, thereby ensuring that light from the light source is collimated to illuminate the incident light hole (3a).

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