GB/T 3978-2008 PDF English
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GB/T 3978-2008: PDF in English (GBT 3978-2008) GB/T 3978-2008
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 17.180.20
K 70
Replacing GB/T 3978-1994
Standard illuminants and geometric conditions
ISSUED ON: JUNE 26, 2008
IMPLEMENTED ON: MARCH 01, 2009
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 CIE standard illuminant ... 7
5 CIE light source ... 10
6 Geometric conditions of color measuring instruments ... 10
Standard illuminants and geometric conditions
1 Scope
This standard specifies the geometric conditions of CIE standard illuminants in
colorimetry, artificial light sources representing illuminants, color measuring
instruments.
This standard is applicable to the application and expression of illuminant and
geometric conditions in color measurement, calculation and evaluation.
2 Normative references
The provisions in following documents become the provisions of this Standard
through reference in this Standard. For the dated references, the subsequent
amendments (excluding corrections) or revisions do not apply to this Standard;
however, parties who reach an agreement based on this Standard are
encouraged to study if the latest versions of these documents are applicable.
For undated references, the latest edition of the referenced document applies.
GB/T 5698 Glossary of color terms
3 Terms and definitions
The terms and definitions as established in GB/T 5698 as well as the following
terms and definitions apply to this standard.
3.1
Illuminant
Radiation with a certain relative spectral power distribution in the wavelength
range that affects the color perception of an object.
3.2
CIE standard illuminants
CIE defined illuminant A and illuminant D65 based on the relative spectral
power distribution.
3.3
CIE sources
The relative spectral power distribution of artificial light sources specified by
CIE which is similar to the relative spectral power distribution of CIE standard
illuminants.
3.4
Geometric conditions
The geometric relationship between the illumination source of the color
measuring instrument and the detector and the color sample of the object,
which is different from the illumination observation conditions in the visual
evaluation.
3.5
Reference plane
The plane on which the measured sample or reference standard is placed
during the measurement.
3.6
Sampling aperture
The illumination area on the reference plane or the area where the receiver
detects the flux, whichever is smaller, shall prevail. When the area of the
illumination area is larger than the area of the detection area, it is called
"overfilled"; when the area of the illumination area is smaller than the area
of the detection area, it is called "underfilled".
3.7
Forty-five degree directional geometry
The incident light illuminates the reflective sample in a direction at 45° from
the normal, the symbol is 45°x.
3.8
Forty-five degree annular geometry
The light source illuminates the reflective sample at an angle of 45° to the
normal from all directions at the same time, the symbol is 45°α.
3.9
Zero degree directional geometry
calculated according to formula (1).
4.1.3 The second column of Table 2 shows the tristimulus values and
chromaticity coordinates of standard illuminant A (380 nm ~ 780 nm, 5 nm
interval) under the CIE 1931 standard chromaticity observer; the second
column of Table 3 gives the tristimulus value and chromaticity coordinates of
the standard illuminant A (380 nm ~ 780 nm, 5 nm interval) under CIE 1964
standard chromaticity observer.
4.2 CIE standard illuminant D65
4.2.1 The relative spectral power distribution SD65 (λ) of the CIE standard
illuminant D65 is determined by the value given in the third column of Table 1.
4.2.2 The relative spectral power distribution of CIE standard illuminant D65 is
extrapolated on the basis of the measured data of daylight. It represents
daylight which has a correlated color temperature of approximately 6500 K (also
known as the nominal correlated color temperature of daylight illuminants).
4.2.3 The third column of Table 1 shows the relative spectral power distribution
of the standard illuminant D65 between 300 nm ~ 780 nm, at 5 nm interval; this
set of values can meet most of the actual calculation needs. Other intermediate
values can be calculated from published values using linear interpolation.
4.2.4 The third column of Table 2 gives the tristimulus values and chromaticity
coordinates of the standard illuminant D65 (380 nm ~ 780 nm, 5 nm interval)
under the CIE 1931 standard chromaticity observer. The third column of Table
3 gives the tristimulus value and chromaticity coordinates of standard illuminant
D65 (380 nm ~ 780 nm, 5 nm interval) under CIE 1964 standard chromaticity
observer.
4.3 Other illuminant D
4.3.1 When D65 cannot be used, it is recommended to use one of the daylight
illuminants D50, D55, or D75. Their spectral power distributions are as shown
in the fourth, fifth, sixth columns of Table 1, respectively. Their tristimulus values
and chromaticity coordinates under CIE 1931 standard chromaticity observer
and CIE 1964 standard chromaticity observer are as shown in the fourth, fifth,
sixth columns of Table 2 and Table 3, respectively.
4.3.2 When none of these daylight illuminants can be used, formulas (2) ~ (7)
can be used to calculate the daylight illuminant under a certain nominal
correlated color temperature (Tcp). The correlated color temperature of the
illuminant given by these formulas is approximately equal to the nominal value.
4.3.3 Chromaticity coordinates of illuminant D
recommended method in this standard is based on the experimental
observation data of wavelength from 330 nm to 700 nm, which is extrapolated
in the wavelength range of 300 nm ~ 330 nm and 700 nm ~ 830 nm. The
extrapolated data is accurate for colorimetric applications, but it is not
recommended for other purposes.
5 CIE light source
5.1 CIE light source A
5.1.1 The gas filled tungsten lamp with correlated color temperature of 2856 K
(c2 = 1.4388 x 10-2 m•K) simulates the artificial light source of standard
illuminant A.
5.1.2 When light source A is used in the ultraviolet region, a lamp with a fused
silica glass bulb or window shall be used.
5.1.3 When the spectral power distribution of the light source is required to be
more accurate, the actual light source used shall be calibrated for spectral
radiance.
5.2 Artificial light source representing standard illuminant D65
5.2.1 It is not recommended to use artificial light sources to realize CIE standard
illuminant D65 or other illuminant D.
5.2.2 By calculating and changing the special metamerism index of the
illuminant, the quality of the daylight simulator used for chromaticity can be
described and evaluated. When the spectral power distribution of the light
source needs to be more accurate, the actual light source used shall be
calibrated for spectral radiance.
6 Geometric conditions of color measuring
instruments
6.1 Geometric conditions of reflection measurement
6.1.1 Diffusion: 8°, including specular components (symbol is di:8°)
The sampling aperture is uniformly illuminated from all directions by the inner
surface of the hemisphere bounded by its plane; the measurement area is
overfilled. The response of the detector to the sampling aperture area is uniform.
The reflected beam axis and the sample center normal are at an angle of 8°.
The radiation reflected by the sampling aperture is uniform in all directions
6.1.6 Alternative geometric conditions of diffusion (symbol is d:0°)
An alternative geometric condition for diffusion is that the exit direction is along
the sample normal, which is a strict geometric condition that does not include
specular reflection.
6.1.7 45° annular/vertical (the symbol is 45°α:0°)
The light whose apex is located at the center of the sampling aperture, central
axis is located on the normal line of the sampling aperture, from all directions
between the two normal cones with half angles of 40° and 50°, respectively,
illuminates the sampling aperture uniformly. The detector whose apex is located
at the center of sampling aperture, central axis is along the normal direction of
the sample, in a normal cone with a half angle of 5°, receives the reflected
radiation uniformly. This geometric condition can minimize the effect of selective
reflection on sample texture and direction. If this lighting geometric condition is
approximated by multiple light sources arranged in a shape close to a circle, or
approximated by a fiber bundle with multiple light exits arranged in a circle and
illuminated by a single light source, the resulting geometric condition is called a
annular/vertical geometry condition (symbol is 45°c:0°).
6.1.8 Vertical/45° annular (symbol is 0°:45°α)
The angle and space conditions satisfy the condition of 45°α:0°, but the light
path is opposite. Therefore, the sampling aperture is illuminated vertically; the
reflected radiation is received by the annular with the center at an angle of 45°
to the normal.
6.1.9 45° single direction/vertical (symbol is 45°x:0°)
The angle and space conditions satisfy the condition of 45°α:0°, but the
radiation is only emitted from one azimuth. Eliminate mirror reflection, highlight
the influence of sample texture and directionality. The symbol x indicates that
the incident beam illuminates the reference plane from an arbitrary direction.
Figure 2 is a schematic diagram of 45° unidirectional/vertical geometric
conditions.
ρw(λ) - The spectral reflectance of the spherical wall under diffusion/diffusion
conditions;
fi - The ratio of the area of the ith opening on the integrating sphere to the
area of the total inner surface of the sphere;
fs - The ratio of the area of the sample hole to the area of the total inner
surface of the sphere;
ρr(λ) -The reflectance of the reference standard.
Formula (8) is based on the characteristics of an ideal integrating sphere; the
effective reflectance of other openings except the sample is 0.
6.2.2 When the geometric conditions meet the requirements of 6.1.1, 6.1.2,
6.1.6, 6.1.7, 6.1.8, 6.1.9, 6.1.10, the measured result is the reflection factor.
When the measurement angle is small enough, the magnitude of the reflection
factor is the same as the magnitude of the radiance factor; when it conforms to
6.1.3 and the integrating sphere is an ideal integrating sphere, the
measurement result is the reflectance.
Note: The measurement result under the condition of 45°x:0° is the radiance
factor β45:0; the measurement result under the condition of 0°:45°x is the
radiance factor β0:45; the measurement result under the condition of di: 8° is the
radiance factor βdi:8, which is close to the radiance factor βd:0; the measurement
result under the 8°:di condition is the reflectance ρ.
6.2.3 Measuring certain types of samples (such as retroreflective materials)
requires different geometric conditions or tolerances. If special lighting and
measurement conditions are used, special instructions are required.
6.2.4 When using the integrating sphere, in order to block the direct light
between the sample and the entrance hole or measuring hole on the spherical
wall, a white-painted screen is required. The total area of the opening of the
integrating sphere shall not exceed 10% of the reflective area inside the sphere.
6.2.5 The diffuse sample can scatter radiation to a direction close to parallel to
its surface; this part of the radiation shall be included in the diffuse reflectance
measurement.
6.2.6 When the integrating sphere is used for the measurement of fluorescent
samples, the relative spectral power distribution of the illumination system will
be replaced by the reflected power and emission power of the sample.
Therefore, the conditions of 45°α:0°, 45°x:0°, 0°:45°α, 0°:45°x are more suitable
for this application.
6.3 Geometric conditions of transmission measurement
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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