JPH03233338A - Integrating sphere inner wall reflectance measuring method - Google Patents

Abstract

PURPOSE:To measure the reflectance of the inner wall of an integrating sphere with high accuracy by recognizing the area of the inner wall of the integrating sphere, that of a photoabsorbing sheet, and their reflectances, and performing relative measurement between the cases where the photoabsorbing sheet is inserted or not inserted to the integrating sphere. CONSTITUTION:The integrating sphere 1 is provided with a receiver 2 at part of an inner wall plane, and a light shielding plate 4 which shields radiation light in the specific direction of a light source. Assuming output from the receiver 2 when the light source 3 having a constant beam of light is lit in the integrating sphere as I0, and the output of the receiver when the photoabsorbing sheet 5 with area of (s) and reflectance of rho1 is placed on the wall plane of the integrating sphere with which the radiation light of the light source is shielded as I1, the reflectance (rho) of the wall plane of the integrating sphere can be found by equation (where, a=I1/I0, c=a/A, A: area of in-sphere wall of integrating sphere). In such a way, since the reflectance of the inner wall plane can be obtained by an inverse operation by measuring the change of the efficiency of the integrating sphere, the measuring of the reflectance under the same optical condition can be performed, which improves the accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to the measurement of characteristics of integrating spheres widely used in the field of optical radiation measurements.

Conventional technology integrating sphere (i.e., as a spherical photometer to measure the total luminous flux of a light source, as an input optical system in a spectroradiometer, or as an optical system for measuring the diffuse reflectance of a material in a spectrophotometer, etc.) Although it is widely used in the field of radiometry, in these applications, the efficiency of the integrating sphere (the ratio of the luminous flux emitted from the melon receiving window to the incident light) is an important characteristic that determines the sensitivity limit and spectral response of the instrument. , this mainly depends on the reflectance of the white paint applied to the inner wall of the integrating sphere.Assuming that the inner wall of the integrating sphere is a completely diffusing surface, the reflectance is expressed as ρ.
(λ), the efficiency of the integrating sphere T(λHL(λ)=k
・ρ(λ)/(1-ρ(λ))・・・0(11)(k
is a constant), that is, a plate. To find the efficiency of the integrating sphere, (
The conventional method for measuring ρ(λ) is to apply the same white paint as that applied to the interior wall surface to a small sample and measure it with a spectrophotometer. There is a known method for measuring T(λ) for a large integrating sphere (for example, for a large integrating sphere). The method of bundling is to turn on a light source whose spectral distribution has been measured outside the integrating sphere, or to guide the light into the integrating sphere and measure the spectral distribution of the light emitted from the receiving window of the integrating sphere. Even if there is a known method to calculate this from the ratio of the spectral distribution outside the integrating sphere, the problem that the invention seeks to solve In the above conventional method, first, the spectral reflectance of a sample coated with the same white paint is calculated. It is not possible to measure the characteristics of the integrating sphere itself when the inner wall surface is dirty or the paint has changed over time. If a material with a very high reflectance (95% to 99%) is used and ρ(λ) approaches 1, as can be seen from equation (6), the error in T(λ) will be amplified. If we measure 98% as 99% with an error of 1%, then T(λ
), the error will be 100 times greater, resulting in a 100% error (the measured value will be doubled).

The measurement accuracy of commonly available reversible spectral reflectance meters is 1.
% or more, and T(λ) for the inner wall surface with high reflectance.
However, the error in the measurement of the inner wall surface of the integrating sphere is very large. ) In many cases, it is not possible to measure the spectral distribution of the light source outside and inside the integrating sphere. Also, this method requires a mechanism for attaching and detaching the spectrometer from the integrating sphere, and it is also necessary to measure while keeping the incident conditions the same, and the light level can vary widely. This invention is a method for solving the problem that there was no means to accurately and easily measure the reflectance of the inner wall surface of an integrating sphere using any of the conventional methods. Regarding the reflectance measurement method, it is characterized by placing a light-absorbing object inside an integrating sphere; it is characterized by interposing a light-shielding plate between the light-absorbing object and the light source; and it is also characterized by a reflective lamp as a light source. It is also characterized in that when multiple light-absorbing objects are used, their reflectances and shapes are made equal.The area A of the inner wall of the action integrating sphere and the area of the light-absorbing sheet are By knowing S and its reflectance ρ1, we can perform comparative measurements with and without a light absorption sheet inside the integrating sphere.
It is possible to find the inner wall reflectance ρ or ρ(λ) of the integrating sphere, and it is also necessary to know the area A of the inner wall of the integrating sphere and the area of the two light absorption sheets (if (3+=32) 2 The reflectance ρ or ρ(λ) of the inner wall of the integrating sphere can be determined by sequentially placing two light-absorbing sheets inside the integrating sphere and performing comparative measurements with the case without the light-absorbing sheet. Without knowing the area A of the inner wall of the sphere or the reflectance ρ1 and ρ of the two light-absorbing sheets (if ρ1 = ρ2), we can sequentially integrate the two light-absorbing sheets for which only the area ratio is known. The reflectance ρ or ρ(λ) of the inner wall surface of the integrating sphere can be determined by performing comparative measurements with the case where no light-absorbing sheet is inserted into the sphere. Figure 1 (above) illustrates the method for measuring the reflectance of the inner wall of an integrating sphere, which is the first embodiment of the present invention. Image 3 is a light beam 4 and 6 are light shielding [5 is a light absorption sheet a] In Fig. 1, the area of the inner wall surface of the integrating sphere 1 is A [m'], and the area of the light absorption sheet 5 is jjs [m"] , the reflectance of the light absorption sheet 5 is ρ1
The light source 3 is a point light source. Even if the light shielding plate 4 is placed in a position where the direct light from the light source 3 does not hit the light receiver 2, Even if it is placed in a position where it is not exposed to direct light.
It is assumed that the receiver 2 outputs a signal proportional to the illuminance on the inner wall surface of integrating sphere 1. In the following analysis, the reflection characteristics of the inner wall surface of integrating sphere 1 are completely diffuse, and the It is assumed that the influence of the light shielding plate 4 on the mutual reflection of light can be ignored.If a light-absorbing object is inserted into the integrating sphere, the apparent average reflectance of the inner wall of the integrating sphere will be lower than when it is not inserted. Although the efficiency T(λ) of the integrating sphere decreases greatly according to equation (11), on the inner wall surface of the integrating sphere whose inner wall surface area is A, there is a light absorption sheet whose area is S and whose reflectance is ρ1(λ). , the apparent average reflectance of the inner wall surface ρ′(
λ) is ρ°(λ〉−ρ(λ)0(i(s/A)(1−ρ1), where ρ(λ) is the true reflectance of the inner wall surface.
(λ)/ρ(λ)))...0(12) Mr. Tona also sets ρ1(λ), s to ρI(λ)<<ρ(λ
), S<<A is selected so that ρ′(λ)−ρ(λ)0(1(s/A)(1−
Although it can be approximated by ρI(λ〉))...0(13), the efficiency T(λ) of the integrating sphere is (1
2), ρ′(λ) in equation (13) is changed to ρ(λ) in equation (11)
First, when the light source 3 is turned on with the light absorption sheet 5 removed from the integrating sphere 1, the output light of the light receiver 2 ζdai (1
1) Using the relationship of formula, I@= to ρ/(1-ρ)
...Also expressed as 0 (14) Here F,
k is a constant and ρ is an unknown quantity, which is the reflectance of the inner wall surface of the integrating sphere.
Since no direct light hits the integrating sphere below the sphere placed on the inner wall of the sphere, the output 11 of the light receiver 2 is (11)
, (12) is expressed as (k is a constant)...0 (15) & In equations (14) & (15), S, A, and ρ1 are known, and the unknown is the simultaneous equation. It is possible to solve ρ and k, that is, board (14)
! (A 15-inch cam is calculated as follows: L a = I + / ■ a c = s / A A is the area of the inner wall of the integrating sphere.) Based on this relationship, using one light-absorbing sheet, The reflectance of the inner wall surface can be measured. Figure 2 G& shows the second embodiment of the present invention.
In Figure 2, 1 is the integral area, 2 is the received light image, and 3 is the light beam.
4 is a light shielding plate and 5 is a light absorbing sheet. In Fig. 2,
The area of the inner wall surface of the integrating sphere 1 is A[. The area of the light absorption sheet 5 is s [m"l. The reflectance of the light absorption sheet 5 is ρ1. The light source 3 is a point light source. The light shielding plate 4 is a light source. Even if the receiver 2 (upper) is placed in a position where the direct light from 3 does not hit the receiver 2, it will output a signal proportional to the illuminance on the inner wall surface of the integrating sphere I. Also, in the following analysis, (Yo
The reflection characteristic of the inner wall surface of the integrating sphere l is completely diffused, and the influence of the light shielding plate 4 on mutual reflection of light within the integrating sphere 1 can be ignored. In FIG. 2, the reflectance of the inner wall surface of the integrating sphere ρ( As in the first embodiment, -a-b ρ= . . . approximately from equations (11) and (13).
(2> (1-a) (1-b) where a = I I/I・b=(1-ρ1)s/Δ A is the area of the inner wall of the integrating sphere, and from this relationship, the first In the same manner as in the second embodiment of the present invention, it is possible to measure the reflectance of the inner wall surface of the integrating sphere l using one light-absorbing sheet.
Compared to the first embodiment, it can be implemented with fewer configurations, and the number of light shielding plates inside the integrating sphere can be reduced.
Moreover, the measurement accuracy can be improved.
In Fig. 3, 1 is an integral region, 2 is a light receiver 4 is a light shielding plate, 5 is a light absorption sheet, and 7 is a reflective lamp.
The structure of the figure (see Figure 1) is similar to that in which the light shielding plate 6 in Figure 1 is removed and the light source 3 is replaced with a reflective lamp 7. By using the reflective lamp 7, it is possible to obtain an effect equivalent to the effect of the combination of the light 11!3 and the light shielding plate 6 in FIG. Although the inner wall reflectance of the integrating sphere can be measured using equation (1) using the same procedure as in the example, the third embodiment of the present invention can be implemented with fewer configurations than the first embodiment. It is possible to reduce the number of light-shielding plates inside the integrating sphere, which can be easily carried out, and the measurement accuracy can be improved. In Figure 4, 1 is the integral, 2 is the received light image, 4 is the light shielding plate, 7 is the reflective lamp, and 8 and 9 are the light absorbing sheets. Assuming that the area of the inner wall surface of l is A[1, the area of light absorption sheet 8 is 431[10'1, the reflectance is ρ1, the area of light absorption sheet 9 is 82[1], the reflectance is ρt, and the light shielding plate 4 is Even if the light receiver 2 is placed in a position where the direct light from the reflective lamp 7 does not hit the light receiver 2, the light receiver 2 (1) outputs a signal proportional to the illuminance on the inner wall surface of the integrating sphere 1. The shaped lamp 7 does not emit light to the wall surface of the integrating sphere 1 on which the light absorption sheet 5 is placed.In addition, in the following analysis, the reflection characteristics of the inner wall surface of the integrating sphere 1 are completely diffused, and the inside of the integrating sphere 1 is It is assumed that the influence of the light shielding plate 4 on mutual reflection of light can be ignored.
When the reflective lamp 7 is turned on with the light-absorbing sheet removed from the integrating sphere l, the output of the light receiver 2 is 0 (y), which is the same as in the first embodiment. 8 is placed on the inner wall surface of the integrating sphere 1 (indicated by the dotted line in Figure 2), the output I+i of the receiver 2 is 1-ρ(1-(s+/A)) as in equation (15). −ρ1(s+/A)(k
is a constant)...0(16) Next, when the light absorption sheet 8 is removed and the light absorption sheet 9 is placed in the same position, the output crab 2 of the light receiver 2 (y (15)
) equation, Saka1-p(L-(st/A)) -9g(sa/A)(k
is a constant)...0(17) 4 By solving the simultaneous equations consisting of equations (14), (16), and (17) for ρ, we can calculate the inner wall reflectance ρ of the integrating sphere. L a+=I+/Is ag=Ia/I・tonam This relational expression can be used to measure the reflectance ρ of the inner wall surface of the integrating sphere 1 using the two light-absorbing sheets 8 and 9. In this example, there is no need to know the area A of the inner wall surface of the integrating sphere, and the reflectance of the inner wall surface of the integrating sphere can be measured by simply knowing the individual areas and reflectances of the two types of light absorption sheets. As a fifth embodiment of the present invention, the reflective lamp 7 in FIG. 4 may be replaced with a point light source. In this case, as in the fourth embodiment, (11), (13) Equation or plate (1-a+
H1-at) (1) I-1) 2) Just j,, a +
= I + / I * a 2 = I s / I · b + = s1 (1 - ρ1) be = se (1 - ρ2) (b + ≠ bi) The following formula was derived and the same procedure as in the fourth example was used. ,(4)
The reflectance of the inner wall surface of the integrating sphere can be measured from the formula.As a sixth embodiment of the present invention, the fourth embodiment (Fig. 4)
By setting the areas of the two light absorption sheets 8 and 9 to be equal, and setting 31 = 32 from equation (3), a I - a 2 is derived, and from equation (5), the light absorption of the two sheets is Since it is possible to determine the reflectance ρ of the inner wall surface of the integrating sphere without knowing the area of the sheet, it is possible to perform even more accurate measurement. Replace 7 with a point light source and use two light absorption sheets 8 and 9
Consider the case where the two light absorbing sheets 8 and 9 are made of the same material.The reflectance of the two light absorbing sheets 8 and 9 can be considered to be equal. Therefore, according to equation (4), ρ
By setting 1=ρ2, L d=sa/s+ is simply derived, and from Equation (6), there is no need to calculate the reflectance of the two types of light-absorbing sheets, and the inner wall reflectance ρ of the integrating sphere can be calculated. However, as an eighth embodiment of the present invention, unit sheets having the same material and area are created, and the light-absorbing sheet 8 in the seventh embodiment is replaced by a unit sheet, and the primary light-absorbing sheet 9 is replaced by two unit sheets. This configuration is convenient because it is not necessary to know the area when creating the light-absorbing sheets, and the ratio of the number of unit sheets used for the light-absorbing sheets 8 and 9 becomes the area ratio of the light-absorbing sheets 8 and 9. In general, there is no wavelength selectivity in the reflectance of the inner wall surface of the integrating sphere.The reflectance ρ described in the first to eighth embodiments above
, ρ1, ρ2 (Y) Means the value obtained by integrating the spectral reflectance of the inner wall surface with the product of the spectral distribution function of the light source and the spectral response function of the receiver. For example, spectral response of the receiver. If the degree is equal to the V(λ) function (standard luminous efficiency)
ρ, ρ1, and ρ2 are expressed as the luminous reflectance for the light source.If the receiver selectively responds to only one wavelength, then let that wavelength be λ, then measure the spectral reflectance ρ(λ). Ninnan Kojo Nen ρ1, ρ! L each ρ
1(λ) and ρ2(λ), replace the light receiver with a spectrometer and perform the measurements in Examples 1 to 8 for each wavelength. It is possible to measure the spectral reflectance ρ(λ) of the wall surface. ,
l is an integral freezer; 4 is a light-shielding K; 7 is a reflective lamp; 8 and 9 are light absorption sheets; 10 is a spectrometer; It does not emit light.Light absorption sheet 8
Assuming that the areas of and 9 are equal, in the following analysis, the reflection characteristics of the inner wall surface of integrating sphere 1 are completely diffuse, and the influence of light shielding plate 4 on the mutual reflection of light within integrating sphere 1 can be ignored. 6o As in the sixth embodiment, with the light absorption sheets 8 and 9 taken out from the integrating sphere 1, first measure the output II (λ) of the spectrometer lO for each wavelength, and then measure the light Measure the output I1 (λ) of the spectrometer 10 when the absorption sheet 8 is placed inside the integrating sphere l.Next, the light absorption sheet 8 is removed and the light absorption sheet 9 is placed inside the integrating sphere l.
When the output Is(λ) of the spectrometer 10 is measured when placed within, aI, a 2 + ρ in equation (5)
'+ρ2, aI(λ), a2(λ), ρ1(
λ) and ρ2(λ), the spectral reflectance ρ(λ) of the inner wall surface of the integrating sphere is calculated by the relational expression: ...0(9)
However, as a tenth embodiment of the present invention, there is a case where the reflective lamp 7 in the ninth embodiment (Fig. 5) is replaced with a point light source and the light absorption sheets 8 and 9 are made of the same material. unthinkable
In the seventh or eighth embodiment, a in equation (6)
l, a 2. ρ1. ρ2, aI(λ), as(λ
), ρI(λ), ρ2(λ),...
(10) Just L d = sa/s + a1 (λ) = I
1(λ)/Is(λ) a之(λ)=I*(λ)/I0(λ) By using this relational expression,
By following the same procedure as in the ninth embodiment, it is not necessary to know the spectral reflectances ρ1 (λ) and ρ2 (λ) of the light absorption sheets 8 and 9, and only the ratio d of their areas can be determined. The spectral reflectance ρ(λ) of the inner wall surface of an integrating sphere can be determined by comparative measurement. This is a method of back-calculating the reflectance of the inner wall surface.It is a method that can measure the reflectance under the same optical conditions (diffuse incidence/diffuse reflection) under which the integrating sphere is functioning.In principle, it is extremely accurate. It is also possible to easily measure the reflectance of the inner wall surface of the integrating sphere.
By using two light-absorbing sheets (with the same reflectance) with known areas (different), it is possible to calculate the inner wall surface of the integrating sphere without having to know the reflectance of the light-absorbing sheets or the area of the inner wall of the integrating sphere. It is now possible to easily measure reflectancea and
By connecting a spectrometer to the integrating sphere, it is possible to more easily measure the spectral reflectance of the inner wall surface of the integrating sphere.In other words, the present invention can easily and accurately measure the reflectance of the inner wall surface of the integrating sphere. This technology realizes a method for measuring the (spectral) efficiency of an integrating sphere, and provides a technology that can be widely applied to the evaluation of the characteristics of an integrating sphere, such as calibrating the (spectral) efficiency of an integrating sphere. , and its practicality is extremely high (t

[Brief explanation of drawings]

FIGS. 1 to 5 are explanatory diagrams of methods for measuring the reflectance of the inner wall of an integrating sphere in different embodiments of the present invention.
... Light reception a 3 ... Light [4, 6 ... Light shielding plate, 5, 8,
9. Light absorption sheet, 7. Reflective lamp, lO.
・Name of spectrometer agent Patent attorney small Nlx;'4 wfi and 2 others Figure whistle

Claims (12)

[Claims] (1) In an integrating sphere characterized by having a light receiver on a part of the inner wall surface and a light shielding plate that blocks emitted light from the light source in a specific direction, a light source with a constant luminous flux is placed inside the integrating sphere. When the light is turned on, the output from the light receiver is I_0, and a light absorption sheet having an area of s and a reflectance of ρ_1 is placed on the wall surface of the integrating sphere where the light emitted from the light source is blocked by the light shielding plate, and the light source is The output of the photoreceiver when the light is turned on is I_1.
When, ρ={1-a(1-c・ρ_1)}/{1-a(1-c
)}...(1) However, a=I_1/I_0 c=s/A A is characterized by determining the reflectance ρ of the wall surface of the integrating sphere based on the relationship of the area of the inner wall of the integrating sphere. A method for measuring the reflectance of the inner wall of an integrating sphere. (2) In an integrating sphere that has a light receiver on a part of its inner wall,
When a light source with a constant luminous flux is lit inside the integrating sphere, the output from the receiver is I_0, the area is s, and the reflectance is ρ_
When the light absorbing sheet 1 is placed on the wall of the integrating sphere and the light source is turned on, the output of the light receiver is I_1, then ρ={1-a-b}/{(1-a)(1 -b)}...
(2) However, a=I_1/I_0 b=(1-ρ_1)s/A A is characterized by determining the reflectance ρ of the wall surface of the integrating sphere based on the relationship of the area of the inner wall of the integrating sphere. A method for measuring the reflectance of the inner wall of an integrating sphere. (3) In the integrating sphere inner wall reflectance measuring method according to claim 1, the light source and the integrating sphere inner wall reflectance are characterized in that a reflective lamp that does not emit light in a specific direction is used instead of using a light shielding plate. rate measurement method. (4) In the integrating sphere inner wall reflectance measurement method according to claim 1 or 3, light reception when a light absorption sheet A having an area s_1 and a reflectance ρ_1 and a light absorption sheet B having an area s_2 and a reflectance ρ_2 are placed. The device outputs are I_1 and I, respectively.
When _2, ρ={s_1(1-ρ_1・a_2)-s_2(1-ρ
_2・a_1)}/{s_1(1-a_2)-s_2(
1-a_1)}...(3) However, a_1=I_1/I_0 a_2=I_2/I_0 A method for measuring the reflectance of the inner wall surface of an integrating sphere, characterized by determining the reflectance ρ of the inner wall surface of the integrating sphere. . (5) In the integrating sphere inner wall reflectance measurement method according to claim 2, light absorption sheet A has an area of s_1 and a reflectance of ρ_1, and light absorption sheet B has an area of s_2 and a reflectance of ρ_2.
When the receiver outputs are I_1 and I_2, respectively, ρ={b_1(a_2-1)-b_2(a_1-1)}
/{(1-a_1) (1-a_2) (b_1-b_2)
}...(4) However, a_1=I_1/I_0 a_2=I_2/I_0 b_1=s_1(1-ρ_1) b_2=s_2(1-ρ_2) (b_1≠b_2) According to the relationship, the integral sphere wall reflectance ρ A method for measuring the reflectance of an inner wall of an integrating sphere, which is characterized by determining . (6) In the integrating sphere inner wall reflectance measurement method according to claim 4, by selecting the areas of the light absorption sheet A and the light absorption sheet B as s_1=s_2, ρ={ρ_
2・a_1−ρ_1・a_2}/{a_1−a_2)}
(5) A method for measuring the reflectance of an inner wall of an integrating sphere, characterized by determining the reflectance ρ of the wall of the integrating sphere from the following relationship. (7) In the integrating sphere inner wall reflectance measuring method according to claim 5, by selecting the reflectance of the light absorption sheet A and the light absorption sheet B as ρ_1=ρ_2, ρ={a
_2-1-d(a_1-1)}/{(1-a_1)(1
-a_2)(1-d)}...(6) However, d=s_
2/s_1 A method for measuring inner wall reflectance of an integrating sphere, characterized in that the wall reflectance ρ of an integrating sphere is determined by the relationship: 2/s_1. (8) In the integrating sphere inner wall reflectance measuring method according to claim 4 or 5, the integrating sphere comprises one or more light absorbing sheets having the same area to constitute the light absorbing sheets A and B. Inner wall reflectance measurement method. (9) In the integrating sphere inner wall reflectance measuring method according to claim 1 or 3, the light receiver is replaced with a spectrometer, and I_
0, I_1 at each wavelength is measured as I_0(λ)
, I_1(λ), then ρ={1-a(λ)(1-c・ρ_1(λ))}/{1
-a(λ)(1-c)}...(7) However, a(λ)=I_1(λ)/I_0(λ)c=s
/A A is the area of the inner wall of the integrating sphere where the area ρ_1(λ) of the inner wall of the integrating sphere is the spectral reflectance of the light absorption sheet, and the spectral reflectance ρ(λ) of the inner wall surface of the integrating sphere is determined from the relationship. Wall reflectance measurement method. (10) In the integrating sphere inner wall reflectance measuring method according to claim 2, the light receiver is replaced with a spectrometer, and I_0, I
The value of _1 measured at each wavelength is I_0(λ), I_
1(λ), ρ={1-a(λ)-b(λ)}/{(1-a(λ))
(1-b(λ))}...(8) However, a(λ)=I
_1(λ)/I_0(λ)b(λ)=(1-ρ_1(λ
)) s/AA is the area ρ_1(λ) of the inner wall of the integrating sphere and the spectral reflectance of the light absorption sheet, so the spectral reflectance ρ(λ) of the wall of the integrating sphere is
) is a method for measuring the reflectance of an inner wall of an integrating sphere. (11) In the integrating sphere inner wall reflectance measuring method according to claim 6, the light receiver is replaced with a spectrometer, I_0, I_1
, I_2 at each wavelength is I_0(λ),
When I_1(λ) and I_2(λ), ρ={ρ_2(λ)・a_1(λ)−ρ_1(λ)・a
_2(λ)}/{a_1(λ)-a_2(λ)}...
(9) A method for measuring the reflectance of an inner wall of an integrating sphere, characterized in that the spectral reflectance ρ(λ) of the wall of the integrating sphere is determined by the following relationship. (12) In the integrating sphere inner wall reflectance measuring method according to claim 7 or 8, the light receiver is replaced with a spectrometer I_0,
I_0(
λ), I_1(λ), I_2(λ), then ρ={
a_2(λ)-1-d(a_1(λ)-1)}/{(1
-a_1(λ))(1-a_2(λ))(1-d)}・
...(10) However, d=s_2/S_1 a_1(λ)=I_1(λ)/I_0(λ)a_2(λ
)=I_2(λ)/I_0(λ) A method for measuring inner wall reflectance of an integrating sphere, characterized in that the spectral reflectance ρ(λ) of the wall surface of the integrating sphere is determined by the relationship: