ASTM E2175-01(2013)
(Practice)Standard Practice for Specifying the Geometry of Multiangle Spectrophotometers
Standard Practice for Specifying the Geometry of Multiangle Spectrophotometers
SIGNIFICANCE AND USE
4.1 This practice is for the use of manufacturers and users of instruments to measure the appearance of gonioapparent materials, those writing standard specifications for such instruments, and others who wish to specify precisely the geometric conditions of multiangle spectrophotometry. A prominent example of industrial usage is the routine application of such measurements by material suppliers and automobile manufacturers to measure the colors of metallic paints and plastics.
SCOPE
1.1 This practice provides a way of specifying the angular and spatial conditions of measurement and angular selectivity of a method of measuring the spectral reflectance factors of opaque gonioapparent materials, for a small number of sets of geometric conditions.
1.2 Measurements to characterize the appearance of retroreflective materials are of such a special nature that they are treated in other ASTM documents and are not included in the scope of this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Standards Content (Sample)
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Designation:E2175 −01 (Reapproved 2013)
Standard Practice for
Specifying the Geometry of Multiangle Spectrophotometers
This standard is issued under the fixed designation E2175; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The appearance of metallic coatings and plastics usually depends on the directions of illumination
and viewing, a phenomenon called “gonioappearance.” This phenomenon is also observed with other
materials, such as lustrous textiles and materials containing pearlescent or interference pigments. The
characteristic appearance of most such materials is accentuated by directional illumination, such as
that provided by the sun on a clear day or a small lamp at night. The variation in color, as a function
of geometry, is usually measured by spectrophotometry with several specified sets of geometric
conditions. Measurement of this kind, at a few selected angles, is called “multiangle
spectrophotometry,” as distinguished from measurement over a broad range of angles, which is called
“goniospectrophotometry.” Spectrophotometric aspects of these measurements, including spectral
resolution and linearity of photometric scales, are treated in other standards, including Practice E308
and Practice E1164. Practice E1767 provides practice for specifying the geometry of measurements.
Retroreflectors exhibit a special kind of gonioappearance, which is treated in otherASTM documents.
The present document provides standard practice for specifying influx and efflux angles, angular
selectivity, spatial distributions of illuminators and receivers, and angular aspects of standardizing the
photometric scale, that are peculiar to multiangle spectrophotometry. Directional illumination
emphasizes the gonioappearance of most materials, but when interference pigments are used, such as
those used in ink to mark paper currency, the effect is observed with diffuse illumination and varying
angles of viewing, so these materials are also measured with diffuse illumination.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice provides a way of specifying the angular
E284 Terminology of Appearance
and spatial conditions of measurement and angular selectivity
E308 PracticeforComputingtheColorsofObjectsbyUsing
of a method of measuring the spectral reflectance factors of
the CIE System
opaque gonioapparent materials, for a small number of sets of
E1164 PracticeforObtainingSpectrometricDataforObject-
geometric conditions.
Color Evaluation
1.2 Measurements to characterize the appearance of retrore-
E1767 Practice for Specifying the Geometries of Observa-
flective materials are of such a special nature that they are
tion and Measurement to Characterize the Appearance of
treated in other ASTM documents and are not included in the
Materials
scope of this standard.
3. Terminology
1.3 This standard does not purport to address all of the
3.1 Fordefinitionsofappearancetermsusedinthispractice,
safety concerns, if any, associated with its use. It is the
refer to Terminology E284.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Significance and Use
bility of regulatory limitations prior to use.
4.1 Thispracticeisfortheuseofmanufacturersandusersof
instruments to measure the appearance of gonioapparent
This practice is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.03 on Geometry. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2013. Published October 2013. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2001. Last previous edition approved in 2008 as E2175 – 01 (2008). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E2175-01R13. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2175−01 (2013)
materials, those writing standard specifications for such specular reflection by an ideal plane mirror at the sampling
instruments, and others who wish to specify precisely the aperture.Anglessubtendedattheoriginandmeasuredfromthe
geometric conditions of multiangle spectrophotometry. A specular direction are called“ aspecular angles” and are posi-
prominent example of industrial usage is the routine applica- tive in sign when measured in the direction toward the normal.
tion of such measurements by material suppliers and automo- The normal and the axis of a directional illuminator define a
bile manufacturers to measure the colors of metallic paints and plane, known as the “plane of incidence.” The specular
plastics. direction necessarily lies in that plane.
6.1.1 To facilitate simple and precise geometric specifica-
5. Components of Apparatus
tion of the sampling aperture, it shall be either circular or
rectangular.
5.1 The apparatus shall consist of one or more illuminators
and one or more spectrometric receivers at fixed or adjustable 6.1.2 To facilitate simple and precise geometric specifica-
angles with respect to a reference plane, a means of positioning tion of directional influx or efflux distributions, they shall be
specimens in a reference plane, a means of indicating the area either conical or pyramidal. For purposes of describing geom-
on the specimen to be measured, shielding to avoid stray light, etry by functional notation, a diffuse distribution may be
considered a conical distribution centered on the normal and
and a means of displaying spectral or colorimetric data and/or
communicating such data to a data-recorder or computer. (The having a half angle of 90 degrees.
terms “light,” “illuminator,” “illumination,” and “illuminance” 6.1.3 In a uniplanar configuration, a directional illuminator
are used here for simplicity, though the corresponding terms
is used, the axes of the receivers lie in the plane of incidence,
“radiant power,” “irradiator,” “irradiation,” and “irradiance” and their positions are specified by aspecular angles. A
would be more accurate when the incident flux includes
uniplanar configuration is illustrated in Fig. 1. To simplify the
ultraviolet flux, as is necessary if the appearance of a fluores- figure, only one receiver is shown.
cent material is measured.)
6.1.3.1 For a conical influx distribution, the flux incident on
the origin comes from an area of a directional illuminator
6. Geometric Types of Apparatus
uniformly filling a circle on a plane normal to the beam. For a
conical efflux distribution, flux from the origin is uniformly
6.1 The geometric configuration of the instrument may be
collected and evaluated over an area of the receiver that is a
uniplanar, annular, circumferential, or diffuse. In all cases, the
specimen is taken to be a flat surface lying in a plane called the circle on a plane normal to the beam.Auniplanar configuration
with conical influx and efflux distributions is illustrated in Fig.
“reference plane,” which is designated the x, y plane. When
there is a single directional illuminator, the x direction is the 2. To simplify the figure, only one receiver is shown.
direction of the projection of the axis of the incident beam on 6.1.3.2 For a pyramidal influx distribution, flux incident on
the reference plane. If there are several directional illuminators the origin comes from an area of a directional illuminator
or a single diffuse illuminator, the direction of the x-axis must uniformlyfillingarectangleonaplanenormaltothebeam.For
be selected and specified. The area of the reference plane on a pyramidal efflux distribution, flux from the origin is uni-
which measurements are made is called the “sampling aper- formly collected and evaluated over an area of the receiver that
ture” and the center of that area is designated the origin, o, of is a rectangle on a plane normal to the beam. A pyramidal
the geometric space used to specify the configuration. The configuration can be used to subtend a small angle in the plane
normal to the sampling aperture, at the origin, is the -z-axis. of incidence, to enhance angular selectivity, but have a large
Angles subtended at the origin and measured from that normal enough solid angle to provide adequate flux for reliable
are called “anormal angles.” The specular direction is the measurements.Auniplanarconfigurationwithpyramidalinflux
direction of the beam from a directional illuminator after and efflux distributions is illustrated in Fig. 3. To simplify the
FIG. 1Uniplanar Configuration
E2175−01 (2013)
FIG. 2Uniplanar Configuration with Conical Influx and Efflux Distributions
FIG. 3Uniplanar Configuration with Pyramidal Influx and Efflux Distributions
figure, only one receiver is shown and the angles δ and ε are 4. To simplify the figure, the angles κ, θ, and η are shown for
i i i
shown for the receiver, but not for the illuminator. the first illuminator only.
6.1.4 In an annular configuration, the incident beam uni- 6.1.5.1 The discrete illuminators shall all have the same
formly fills the space between two right-circular cones, with
nominal angle of incidence, for a given measurement.
their axes on the normal and apices at the origin. An annular
6.1.6 In a diffuse configuration, the incident flux is diffuse.
configuration can be used to provide a flux distribution with a
Ideally, the illuminator illuminates the sampling aperture at all
small range of anormal angles, to enhance anormal angular
angles within the hemisphere on the -z side of the reference
selectivity, but of large enough solid angle to provide adequate
plane, except those directions occupied by receivers. The use
flux for reliable measurements. The nominal angle of an
of an integrating sphere to produce uniform diffuse illumina-
annular distribution is the average of the half-angles of the two
tion requires non-selective diffusing b
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