This paper describes the results of an interlaboratory comparison of working standards made on behalf of Committee E-1.3.1. (Colorimetry) of the Commission Internationale de l’Eclairage. Thirty laboratories from 15 different countries participated and spectral reflectance (βλ), luminous reflectance (β), and chromaticity coordinates (x,y) were reported for four glossy ceramic tiles—near-white, light grey, dark grey, and near-black. The results have been analyzed in two groups depending on whether the illumination and light collection were directional or diffuse. A very considerable spread was found in each group of results, as well as a significant difference between the mean values of β in each group; the causes have been discussed. With a selected group of laboratories, however, the spread was very much smaller; use of calibrated white, grey, and near-black standards is recommended as a means of extending this agreement to laboratories which are not in a position to adopt all the refinements available to standardizing laboratories.
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
The column headed “Geometry” gives the mean angle of incidence of the beam illuminating the sample, followed by the angle to the normal at which the light is collected. Where an integrating sphere is used, this is shown by the letter D.
Table II
List of colorimeters used in survey.
Code
Type of instrument
Geometry
Total angular spread
Illuminated area
Working standard
Illumination
Collection
B
Colormaster
45/0
Small
14°
⋯
⋯
C1
Donaldson
0/45
2°
12°
1.0×1.5 cm
MgO
C2
Colormaster
45/0
Small
14°
3.0×2.0 cm
Vitrolite
D1
Colormaster
45/0
Small
14°
1.0×2.5 cm
Vitrolite
D2
Gardner Color-Difference Meter
45/0
Small
60°
0.5×1.5 cm
Vitrolite
E1
Colormaster
45/0
Small
14°
3.0×2.0 cm
Vitrolite
E2
Hilger & Watts J.40
0/45
Small
15°
0.8-cm diam
Vitrolite
G
Hilger & Watts J.20
0/45
Small
15°
0.8-cm diam
MgO
H1
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H2
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H3
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H4
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
O
Djomkina
⋯
⋯
⋯
⋯
⋯
R
Colormaster
45/0
Small
14°
3.1×4.4 cm
Vitrolite
T
Zeiss Elko
45/0
18°
28°
2.8-cm diam
U
Color Eye
D/45
D
⋯
⋯
MgO
W2
Zeiss Elrepho
D/0
D
7°
2.5-cm diam
AB
Hilger & Watts J.40
0/45
Small
15°
0.8-cm diam
MgO
AC1
Zeiss Elko
45/0
18°
28°
1.0×1.6 cm
Pressed MgO
AC2
Zeiss Elrepho
D/0
D
7°
3.0-cm diam
Pressed MgO
AD
Color Eye
D/45
D
⋯
⋯
Vitrolite
AE
Donaldson
0/45
2°
12°
1.0×1.5 cm
AI1
Color Eye
D/45
D
⋯
⋯
Pressed MgO
AI2
Colormaster
45/0
Small
14°
⋯
Pressed MgO
AI3
Color Eye
D/45
D
⋯
⋯
BaSO4
Table III
Differences of reflectance between circulated tiles and reference tiles. (Average of four measurements on a Color-master and four on a Hilger & Watts J40 Colourmeter).
Δβ (βMgO = 100 units)
Set
11 572
9862
9855
11 616
A
+0.8
+0.05
+0.30
+0.20
B
−0.1
+0.10
+0.10
+0.20
C
+0.4
−0.10
+0.70
+0.05
D
−0.1
−0.25
+0.50
+0.10
E
0
0
0
0
F
0
+0.20
+0.05
+0.25
G
−0.1
−0.05
+0.20
0
H
−0.1
+0.05
+0.70
+0.20
I
−0.2
+0.05
+0.10
+0.15
J
+0.3
−0.10
−0.10
+0.05
K
−0.2
−0.10
+0.80
+0.25
M
0
−0.20
+0.15
+0.20
N
+0.7
+0.15
+0.35
+0.10
O
0
−0.10
+0.50
+0.15
P
−0.1
−0.05
+0.55
+0.15
Q
−0.3
−0.10
+0.45
+0.10
R
−0.4
−0.45
+0.60
−0.05
T
−0.7
−0.10
+0.60
+0.20
U
−0.4
−0.20
+0.25
+0.10
V
+0.3
−0.05
+0.55
+0.20
W
+0.2
−0.15
+0.10
+0.20
Y
−0.5
+0.05
+0.50
+0.15
AB
−0.5
−0.30
+0.55
+0.20
AC
−0.3
−0.40
+0.15
−0.05
AD
−0.4
0
+0.65
+0.10
AE
+0.2
−0.10
+0.50
+0.05
AI
−0.2
+0.05
+0.50
+0.20
Table IV
Distribution of measurements of reflectance.
(Illuminant SC)
Range of β
Spectrophotometers
Colorimeters
45°/0° or 0°/45°
Integrating spheres
45°/0° or 0°/45°
Integrating spheres
Tile No. 11 572
Above 88.9
x
x
88.5–88.9
x
x
88.0–88.4
x
x
xx
87.5–87.9
x
xx
87.0–87.4
x
x
86.5–86.9
xx
xx
x
86.0–86.4
xxx
x
xxxxx
85.5–85.9
x
xx
xx
85.0–85.4
xx
xxxxxxx
xx
xx
84.5–84.9
xxxxxxx
x
xxxx
84.0–84.4
xx
Tile No. 9862
Above 63.4
x
63.0–63.4
x
62.5–62.9
x
x
62.0–62.4
x
x
x
61.5–61.9
xx
x
x
61.0–61.4
xxxx
x
xxxx
60.5–60.9
xx
xxx
xxxx
x
60.0–60.4
xx
xxxxxxx
x
xxxx
59.5–59.9
xxxxxx
xxxx
59.0–59.4
xx
x
x
Tile No. 9855
Above 31.4
x
x
31.0–31.4
x
30.5–30.9
x
30.0–30.4
x
29.5–29.9
xx
x
xx
x
29.0–29.4
xxxxxx
xxxxx
xxxxxxx
xxx
28.5–28.9
xx
xxxxxxxxx
xxx
x
28.0–28.4
xxxxx
xx
x
27.5–27.9
xxx
Tile No. 11 616
Above 6.4
xxx
6.3–6.4
6.1–6.2
5.9–6.0
x
xx
x
5.7–5.8
5.5–5.6
xx
x
xx
5.3–5.4
x
xx
xx
5.1–5.2
xxxxxxxxx
xxxxxxx
xxxxxxxxxx
xxxx
4.9–5.0
x
xxx
xx
4.7–4.8
xxx
x
4.5–4.6
x
Table V
Distribution of measurements of relative reflectance (β= β′/β11 572).
(Illuminant SC)
Range of β′
Spectrophotometers
Colorimeters
45°/0° or 0°/45°
Integrating spheres
45°/0° or 0°/45°
Integrating spheres
Tile No. 9862
Above 71.9
x
71.7–71.9
x
71.4–71.6
x
71.1–71.3
x
xx
70.8–71.0
xxxxxx
xxxxxxxxx
xx
x
70.5–70.7
xxx
xxxxx
xxxx
x
70.2–70.4
xxx
xxxx
x
69.9–70.1
xx
xxxx
69.6–69.8
x
xxx
x
69.3–69.5
xxx
Tile No. 9855
Above 35.4
xx
35.2–35.4
x
34.9–35.1
x
34.6–34.8
x
x
34.3–34.5
x
xx
xx
34.0–34.2
xxx
x
xxxx
x
33.7–33.9
xxxx
xxxxxxx
xx
x
33.4–33.6
xxx
xxxxxx
xx
33.1–33.3
x
xx
xx
x
32.8–33.0
x
xxx
32.5–32.7
xx
32.2–32.4
xx
Tile No. 11 616
Above 7.2
xxx
7.1–7.2
6.9–7.0
xx
6.7–6.8
x
6.5–6.6
x
xx
6.3–6.4
x
xxxx
6.1–6.2
xx
xxxxxx
xxxx
xxxx
5.9–6.0
xxxxxxx
xx
xxxxxxx
5.7–5.8
xx
xxx
xxx
5.5–5.6
x
xx
x
5.3–5.4
x
Table VI
Averages and spreads of results. Each set of results is given as M±s, where M is the mean result, and s is the rms deviation from this mean. The figure in brackets gives the number of results included in each case.
(Illuminant SC)
45°/0° and 0°/45° instruments
Integrating sphere instruments
Spectrophotometers
Colorimeters
Spectrophotometers
Colorimeters
(a) Reflectance, β
11 572
86.6 ±1.1 (11)
86.3 ±1.1 (14)
85.3 ±0.8 (21)
84.8 ±0.3 (6)
9862
61.1 ±0.7 (11)
60.7 ±1.0 (17)
60.4 ±1.0 (20)
60.1 ±0.5 (6)
9855
29.2 ±0.5 (11)
28.8 ±0.6 (17)
28.9 ±0.5 (19)
29.0 ±0.4 (6)
11 616
5.10±0.10 (11)
5.15±0.25 (17)
5.15±0.30 (17)
5.35±0.15 (5)
(b) Reflectance relative to tile No. 11 572 (β′)
9862
70.5 ±0.4 (12)
70.1 ±0.5 (14)
70.7 ±0.3 (18)
70.8 ±0.5 (6)
9855
33.8 ±0.3 (12)
33.3 ±0.6 (14)
33.9 ±0.5 (18)
34.2 ±0.5 (6)
11 616
5.90±0.15 (12)
6.00±0.30 (14)
6.05±0.35 (17)
6.30±0.20 (5)
(c) Chromaticity coordinates
11 572
x
0.3118±0.0010 (12)
0.3120±0.0007 (14)
0.3121±0.0004 (21)
0.3122±0.0008 (6)
y
0.3191±0.0018
0.3191 ±0.0008
0.3198±0.0005
0.3195±0.0006
9862
x
0.3145±0.0014 (12)
0.3148±0.0013 (17)
0.3149±0.0004 (20)
0.3146±0.0012 (6)
y
0.3251±0.0013
0.3247±0.0014
0.3257±0.0005
0.3142±0.0015
9855
x
0.3146±0.0011 (12)
0.3144±0.0015 (17)
0.3144±0.0006 (19)
0.3135±0.0019 (6)
y
0.3258±0.0014
0.3248±0.0020
0.3259±0.0007
0.3250±0.0011
11 616
x
0.2973±0.0017 (12)
0.2978±0.0023 (18)
0.2978±0.0014 (17)
0.2997±0.0012 (5)
y
0.3020±0.0017
0.3010±0.0031
0.3028±0.0013
0.3024±0.0010
Table VII
Analysis of results from General Electric spectrophotometers. Each set of results is given as M±s, where M is the mean result and s is the rms deviation from this mean. The figure in brackets gives the number of results included in each case.
(Illuminant SC)
All instruments
Using NBS white standard
Using other white standards
Reflectance (β)
11 572
85.0 ±0.6 (14)
84.7 ±0.3 (6)
85.3 ±0.6 (8)
9862
60.0 ±0.6 (14)
59.7 ±0.4 (6)
60.2 ±0.6 (8)
9855
28.7 ±0.4 (14)
28.6 ±0.3 (6)
28.7 ±0.4 (8)
11 616
5.10±0.25 (14)
5.10±0.30 (6)
5.10±0.20 (8)
Reflectance relative to tile No. 11 572 (β′)
9862
70.6 ±0.3 (14)
70.5 ±0.3 (6)
70.6 ±0.4 (8)
9855
33.7 ±0.4 (14)
33.8 ±0.4 (6)
33.6 ±0.3 (8)
11616
6.00±0.30 (14)
6.00±0.35 (6)
5.95±0.25 (8)
Chromaticity coordinates
11 572
x
0.3121±0.0004 (14)
0.3125±0.0003 (6)
0.3119±0.0003 (8)
y
0.3198±0.0005
0.3203 ±0.0004
0.3195±0.0003
9862
x
0.3149±0.0005 (14)
0.3153 ±0.0004 (6)
0.3147±0.0003 (8)
y
0.3257±0.0005
0.3261 ±0.0002
0.3254±0.0005
9855
x
0.3144±0.0007 (14)
0.3150±0.0002 (6)
0.3140±0.0004 (8)
y
0.3259±0.0007
0.3266±0.0004
O.3256±0.0006
11 616
x
0.2974±0.0012 (14)
0.2979±0.0015 (6)
0.2970±0.0005 (8)
y
0.3025±0.0011
0.3032±0.0011
0.3020±0.0009
Table VIII
Variation of reflectance across a tile.
Tile
Range of reflectance in the less uniform of two tiles measured at NPL
Range of reflectance in the least uniform of three tiles measured at I.C.
The column headed “Geometry” gives the mean angle of incidence of the beam illuminating the sample, followed by the angle to the normal at which the light is collected. Where an integrating sphere is used, this is shown by the letter D.
Table II
List of colorimeters used in survey.
Code
Type of instrument
Geometry
Total angular spread
Illuminated area
Working standard
Illumination
Collection
B
Colormaster
45/0
Small
14°
⋯
⋯
C1
Donaldson
0/45
2°
12°
1.0×1.5 cm
MgO
C2
Colormaster
45/0
Small
14°
3.0×2.0 cm
Vitrolite
D1
Colormaster
45/0
Small
14°
1.0×2.5 cm
Vitrolite
D2
Gardner Color-Difference Meter
45/0
Small
60°
0.5×1.5 cm
Vitrolite
E1
Colormaster
45/0
Small
14°
3.0×2.0 cm
Vitrolite
E2
Hilger & Watts J.40
0/45
Small
15°
0.8-cm diam
Vitrolite
G
Hilger & Watts J.20
0/45
Small
15°
0.8-cm diam
MgO
H1
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H2
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H3
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
H4
Colormaster
45/0
Small
14°
3.0×2.0 cm
MgO
O
Djomkina
⋯
⋯
⋯
⋯
⋯
R
Colormaster
45/0
Small
14°
3.1×4.4 cm
Vitrolite
T
Zeiss Elko
45/0
18°
28°
2.8-cm diam
U
Color Eye
D/45
D
⋯
⋯
MgO
W2
Zeiss Elrepho
D/0
D
7°
2.5-cm diam
AB
Hilger & Watts J.40
0/45
Small
15°
0.8-cm diam
MgO
AC1
Zeiss Elko
45/0
18°
28°
1.0×1.6 cm
Pressed MgO
AC2
Zeiss Elrepho
D/0
D
7°
3.0-cm diam
Pressed MgO
AD
Color Eye
D/45
D
⋯
⋯
Vitrolite
AE
Donaldson
0/45
2°
12°
1.0×1.5 cm
AI1
Color Eye
D/45
D
⋯
⋯
Pressed MgO
AI2
Colormaster
45/0
Small
14°
⋯
Pressed MgO
AI3
Color Eye
D/45
D
⋯
⋯
BaSO4
Table III
Differences of reflectance between circulated tiles and reference tiles. (Average of four measurements on a Color-master and four on a Hilger & Watts J40 Colourmeter).
Δβ (βMgO = 100 units)
Set
11 572
9862
9855
11 616
A
+0.8
+0.05
+0.30
+0.20
B
−0.1
+0.10
+0.10
+0.20
C
+0.4
−0.10
+0.70
+0.05
D
−0.1
−0.25
+0.50
+0.10
E
0
0
0
0
F
0
+0.20
+0.05
+0.25
G
−0.1
−0.05
+0.20
0
H
−0.1
+0.05
+0.70
+0.20
I
−0.2
+0.05
+0.10
+0.15
J
+0.3
−0.10
−0.10
+0.05
K
−0.2
−0.10
+0.80
+0.25
M
0
−0.20
+0.15
+0.20
N
+0.7
+0.15
+0.35
+0.10
O
0
−0.10
+0.50
+0.15
P
−0.1
−0.05
+0.55
+0.15
Q
−0.3
−0.10
+0.45
+0.10
R
−0.4
−0.45
+0.60
−0.05
T
−0.7
−0.10
+0.60
+0.20
U
−0.4
−0.20
+0.25
+0.10
V
+0.3
−0.05
+0.55
+0.20
W
+0.2
−0.15
+0.10
+0.20
Y
−0.5
+0.05
+0.50
+0.15
AB
−0.5
−0.30
+0.55
+0.20
AC
−0.3
−0.40
+0.15
−0.05
AD
−0.4
0
+0.65
+0.10
AE
+0.2
−0.10
+0.50
+0.05
AI
−0.2
+0.05
+0.50
+0.20
Table IV
Distribution of measurements of reflectance.
(Illuminant SC)
Range of β
Spectrophotometers
Colorimeters
45°/0° or 0°/45°
Integrating spheres
45°/0° or 0°/45°
Integrating spheres
Tile No. 11 572
Above 88.9
x
x
88.5–88.9
x
x
88.0–88.4
x
x
xx
87.5–87.9
x
xx
87.0–87.4
x
x
86.5–86.9
xx
xx
x
86.0–86.4
xxx
x
xxxxx
85.5–85.9
x
xx
xx
85.0–85.4
xx
xxxxxxx
xx
xx
84.5–84.9
xxxxxxx
x
xxxx
84.0–84.4
xx
Tile No. 9862
Above 63.4
x
63.0–63.4
x
62.5–62.9
x
x
62.0–62.4
x
x
x
61.5–61.9
xx
x
x
61.0–61.4
xxxx
x
xxxx
60.5–60.9
xx
xxx
xxxx
x
60.0–60.4
xx
xxxxxxx
x
xxxx
59.5–59.9
xxxxxx
xxxx
59.0–59.4
xx
x
x
Tile No. 9855
Above 31.4
x
x
31.0–31.4
x
30.5–30.9
x
30.0–30.4
x
29.5–29.9
xx
x
xx
x
29.0–29.4
xxxxxx
xxxxx
xxxxxxx
xxx
28.5–28.9
xx
xxxxxxxxx
xxx
x
28.0–28.4
xxxxx
xx
x
27.5–27.9
xxx
Tile No. 11 616
Above 6.4
xxx
6.3–6.4
6.1–6.2
5.9–6.0
x
xx
x
5.7–5.8
5.5–5.6
xx
x
xx
5.3–5.4
x
xx
xx
5.1–5.2
xxxxxxxxx
xxxxxxx
xxxxxxxxxx
xxxx
4.9–5.0
x
xxx
xx
4.7–4.8
xxx
x
4.5–4.6
x
Table V
Distribution of measurements of relative reflectance (β= β′/β11 572).
(Illuminant SC)
Range of β′
Spectrophotometers
Colorimeters
45°/0° or 0°/45°
Integrating spheres
45°/0° or 0°/45°
Integrating spheres
Tile No. 9862
Above 71.9
x
71.7–71.9
x
71.4–71.6
x
71.1–71.3
x
xx
70.8–71.0
xxxxxx
xxxxxxxxx
xx
x
70.5–70.7
xxx
xxxxx
xxxx
x
70.2–70.4
xxx
xxxx
x
69.9–70.1
xx
xxxx
69.6–69.8
x
xxx
x
69.3–69.5
xxx
Tile No. 9855
Above 35.4
xx
35.2–35.4
x
34.9–35.1
x
34.6–34.8
x
x
34.3–34.5
x
xx
xx
34.0–34.2
xxx
x
xxxx
x
33.7–33.9
xxxx
xxxxxxx
xx
x
33.4–33.6
xxx
xxxxxx
xx
33.1–33.3
x
xx
xx
x
32.8–33.0
x
xxx
32.5–32.7
xx
32.2–32.4
xx
Tile No. 11 616
Above 7.2
xxx
7.1–7.2
6.9–7.0
xx
6.7–6.8
x
6.5–6.6
x
xx
6.3–6.4
x
xxxx
6.1–6.2
xx
xxxxxx
xxxx
xxxx
5.9–6.0
xxxxxxx
xx
xxxxxxx
5.7–5.8
xx
xxx
xxx
5.5–5.6
x
xx
x
5.3–5.4
x
Table VI
Averages and spreads of results. Each set of results is given as M±s, where M is the mean result, and s is the rms deviation from this mean. The figure in brackets gives the number of results included in each case.
(Illuminant SC)
45°/0° and 0°/45° instruments
Integrating sphere instruments
Spectrophotometers
Colorimeters
Spectrophotometers
Colorimeters
(a) Reflectance, β
11 572
86.6 ±1.1 (11)
86.3 ±1.1 (14)
85.3 ±0.8 (21)
84.8 ±0.3 (6)
9862
61.1 ±0.7 (11)
60.7 ±1.0 (17)
60.4 ±1.0 (20)
60.1 ±0.5 (6)
9855
29.2 ±0.5 (11)
28.8 ±0.6 (17)
28.9 ±0.5 (19)
29.0 ±0.4 (6)
11 616
5.10±0.10 (11)
5.15±0.25 (17)
5.15±0.30 (17)
5.35±0.15 (5)
(b) Reflectance relative to tile No. 11 572 (β′)
9862
70.5 ±0.4 (12)
70.1 ±0.5 (14)
70.7 ±0.3 (18)
70.8 ±0.5 (6)
9855
33.8 ±0.3 (12)
33.3 ±0.6 (14)
33.9 ±0.5 (18)
34.2 ±0.5 (6)
11 616
5.90±0.15 (12)
6.00±0.30 (14)
6.05±0.35 (17)
6.30±0.20 (5)
(c) Chromaticity coordinates
11 572
x
0.3118±0.0010 (12)
0.3120±0.0007 (14)
0.3121±0.0004 (21)
0.3122±0.0008 (6)
y
0.3191±0.0018
0.3191 ±0.0008
0.3198±0.0005
0.3195±0.0006
9862
x
0.3145±0.0014 (12)
0.3148±0.0013 (17)
0.3149±0.0004 (20)
0.3146±0.0012 (6)
y
0.3251±0.0013
0.3247±0.0014
0.3257±0.0005
0.3142±0.0015
9855
x
0.3146±0.0011 (12)
0.3144±0.0015 (17)
0.3144±0.0006 (19)
0.3135±0.0019 (6)
y
0.3258±0.0014
0.3248±0.0020
0.3259±0.0007
0.3250±0.0011
11 616
x
0.2973±0.0017 (12)
0.2978±0.0023 (18)
0.2978±0.0014 (17)
0.2997±0.0012 (5)
y
0.3020±0.0017
0.3010±0.0031
0.3028±0.0013
0.3024±0.0010
Table VII
Analysis of results from General Electric spectrophotometers. Each set of results is given as M±s, where M is the mean result and s is the rms deviation from this mean. The figure in brackets gives the number of results included in each case.
(Illuminant SC)
All instruments
Using NBS white standard
Using other white standards
Reflectance (β)
11 572
85.0 ±0.6 (14)
84.7 ±0.3 (6)
85.3 ±0.6 (8)
9862
60.0 ±0.6 (14)
59.7 ±0.4 (6)
60.2 ±0.6 (8)
9855
28.7 ±0.4 (14)
28.6 ±0.3 (6)
28.7 ±0.4 (8)
11 616
5.10±0.25 (14)
5.10±0.30 (6)
5.10±0.20 (8)
Reflectance relative to tile No. 11 572 (β′)
9862
70.6 ±0.3 (14)
70.5 ±0.3 (6)
70.6 ±0.4 (8)
9855
33.7 ±0.4 (14)
33.8 ±0.4 (6)
33.6 ±0.3 (8)
11616
6.00±0.30 (14)
6.00±0.35 (6)
5.95±0.25 (8)
Chromaticity coordinates
11 572
x
0.3121±0.0004 (14)
0.3125±0.0003 (6)
0.3119±0.0003 (8)
y
0.3198±0.0005
0.3203 ±0.0004
0.3195±0.0003
9862
x
0.3149±0.0005 (14)
0.3153 ±0.0004 (6)
0.3147±0.0003 (8)
y
0.3257±0.0005
0.3261 ±0.0002
0.3254±0.0005
9855
x
0.3144±0.0007 (14)
0.3150±0.0002 (6)
0.3140±0.0004 (8)
y
0.3259±0.0007
0.3266±0.0004
O.3256±0.0006
11 616
x
0.2974±0.0012 (14)
0.2979±0.0015 (6)
0.2970±0.0005 (8)
y
0.3025±0.0011
0.3032±0.0011
0.3020±0.0009
Table VIII
Variation of reflectance across a tile.
Tile
Range of reflectance in the less uniform of two tiles measured at NPL
Range of reflectance in the least uniform of three tiles measured at I.C.