ASTM G178-16(2023)
(Practice)Standard Practice for Determining the Activation Spectrum of a Material (Wavelength Sensitivity to an Exposure Source) Using the Sharp Cut-On Filter or Spectrographic Technique
Standard Practice for Determining the Activation Spectrum of a Material (Wavelength Sensitivity to an Exposure Source) Using the Sharp Cut-On Filter or Spectrographic Technique
SIGNIFICANCE AND USE
4.1 The activation spectrum identifies the spectral region(s) of the specific exposure source used that may be primarily responsible for changes in appearance and/or physical properties of the material.
4.2 The spectrographic technique uses a prism or grating spectrograph to determine the effect on the material of isolated narrow spectral bands of the light source, each in the absence of other wavelengths.
4.3 The sharp cut-on filter technique uses a specially designed set of sharp cut-on UV/visible transmitting glass filters to determine the relative actinic effects of individual spectral bands of the light source during simultaneous exposure to wavelengths longer than the spectral band of interest.
4.4 Both the spectrographic and filter techniques provide activation spectra, but they differ in several respects:
4.4.1 The spectrographic technique generally provides better resolution since it determines the effects of narrower spectral portions of the light source than the filter technique.
4.4.2 The filter technique is more representative of the polychromatic radiation to which samples are normally exposed with different, and sometimes antagonistic, photochemical processes often occurring simultaneously. However, since the filters only transmit wavelengths longer than the cut-on wavelength of each filter, antagonistic processes by wavelengths shorter than the cut-on are eliminated.
4.4.3 In the filter technique, separate specimens are used to determine the effect of the spectral bands and the specimens are sufficiently large for measurement of both mechanical and optical changes. In the spectrographic technique, except in the case of spectrographs as large as the Okazaki type (1),4 a single small specimen is used to determine the relative effects of all the spectral bands. Thus, property changes are limited to those that can be measured on very small sections of the specimen.
4.5 The information provided by activation spectra on the spectral r...
SCOPE
1.1 This practice describes the determination of the relative actinic effects of individual spectral bands of an exposure source on a material. The activation spectrum is specific to the light source to which the material is exposed to obtain the activation spectrum. A light source with a different spectral power distribution will produce a different activation spectrum.
1.2 This practice describes two procedures for determining an activation spectrum. One uses sharp cut-on UV/visible transmitting filters and the other uses a spectrograph to determine the relative degradation caused by individual spectral regions.
Note 1: Other techniques can be used to isolate the effects of individual spectral bands of a light source, for example, interference filters.
1.3 The techniques are applicable to determination of the spectral effects of solar radiation and laboratory accelerated test devices on a material. They are described for the UV region, but can be extended into the visible region using different cut-on filters and appropriate spectrographs.
1.4 The techniques are applicable to a variety of materials, both transparent and opaque, including plastics, paints, inks, textiles and others.
1.5 The optical and/or physical property changes in a material can be determined by various appropriate methods. The methods of evaluation are beyond the scope of this practice.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
Note 2: There is no ISO standard that is equivalent to this standard.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Develop...
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G178 − 16 (Reapproved 2023)
Standard Practice for
Determining the Activation Spectrum of a Material
(Wavelength Sensitivity to an Exposure Source) Using the
Sharp Cut-On Filter or Spectrographic Technique
This standard is issued under the fixed designation G178; 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.
1. Scope 1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This practice describes the determination of the relative
ization established in the Decision on Principles for the
actinic effects of individual spectral bands of an exposure
Development of International Standards, Guides and Recom-
source on a material. The activation spectrum is specific to the
mendations issued by the World Trade Organization Technical
light source to which the material is exposed to obtain the
Barriers to Trade (TBT) Committee.
activation spectrum. A light source with a different spectral
power distribution will produce a different activation spectrum.
2. Referenced Documents
1.2 This practice describes two procedures for determining
2.1 ASTM Standards:
an activation spectrum. One uses sharp cut-on UV/visible
D256 Test Methods for Determining the Izod Pendulum
transmitting filters and the other uses a spectrograph to
Impact Resistance of Plastics
determine the relative degradation caused by individual spec-
D638 Test Method for Tensile Properties of Plastics
tral regions.
D822 Practice for Filtered Open-Flame Carbon-Arc Expo-
NOTE 1—Other techniques can be used to isolate the effects of
sures of Paint and Related Coatings
individual spectral bands of a light source, for example, interference
filters.
D1435 Practice for Outdoor Weathering of Plastics
D1499 Practice for Filtered Open-Flame Carbon-Arc Expo-
1.3 The techniques are applicable to determination of the
sures of Plastics
spectral effects of solar radiation and laboratory accelerated
D2244 Practice for Calculation of Color Tolerances and
test devices on a material. They are described for the UV
Color Differences from Instrumentally Measured Color
region, but can be extended into the visible region using
Coordinates
different cut-on filters and appropriate spectrographs.
D2565 Practice for Xenon-Arc Exposure of Plastics In-
1.4 The techniques are applicable to a variety of materials,
tended for Outdoor Applications
both transparent and opaque, including plastics, paints, inks,
D4141 Practice for Conducting Black Box and Solar Con-
textiles and others.
centrating Exposures of Coatings
1.5 The optical and/or physical property changes in a
D4329 Practice for Fluorescent Ultraviolet (UV) Lamp Ap-
material can be determined by various appropriate methods.
paratus Exposure of Plastics
The methods of evaluation are beyond the scope of this
D4364 Practice for Performing Outdoor Accelerated Weath-
practice.
ering Tests of Plastics Using Concentrated Sunlight
D4459 Practice for Xenon-Arc Exposure of Plastics In-
1.6 This standard does not purport to address all of the
tended for Indoor Applications
safety concerns, if any, associated with its use. It is the
D4508 Test Method for Chip Impact Strength of Plastics
responsibility of the user of this standard to establish appro-
(Withdrawn 2016)
priate safety, health, and environmental practices and deter-
D4587 Practice for Fluorescent UV-Condensation Expo-
mine the applicability of regulatory limitations prior to use.
sures of Paint and Related Coatings
NOTE 2—There is no ISO standard that is equivalent to this standard.
1 2
This practice is under the jurisdiction of ASTM Committee G03 on Weathering For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Durability and is the direct responsibility of Subcommittee G03.01 on Joint contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Weathering Projects. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Feb. 1, 2023. Published February 2023. Originally the ASTM website.
approved in 2003. Last previous edition approved in 2016 as G178 – 16. DOI: The last approved version of this historical standard is referenced on www.ast-
10.1520/G0178-16R23. m.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G178 − 16 (2023)
D5031 Practice for Enclosed Carbon-Arc Exposure Tests of 3.2.4 sharp cut-on UV/VIS transmitting glass filters,
Paint and Related Coatings n—filters that screen out the short wavelengths and transmit
D6360 Practice for Enclosed Carbon-Arc Exposures of Plas- radiation longer than the cut-on wavelength. The transmittance
tics increases sharply from 5 %, the cut-on wavelength, to 72 %
D6695 Practice for Xenon-Arc Exposures of Paint and within a spectral range of about 20 nm. They are also referred
Related Coatings to as longpass filters.
E275 Practice for Describing and Measuring Performance of
3.2.5 spectral band, n—the spectral region defined by the
Ultraviolet and Visible Spectrophotometers
difference in transmittance of a pair of the sharp cut-on
E313 Practice for Calculating Yellowness and Whiteness
UV/VIS transmitting glass filters. It is also referred to as the
Indices from Instrumentally Measured Color Coordinates
incremental ultraviolet.
E925 Practice for Monitoring the Calibration of Ultraviolet-
3.2.6 spectral band pass, n—the spectral range of the
Visible Spectrophotometers whose Spectral Bandwidth
spectral band at the delta 20 % transmittance level. It is the
does not Exceed 2 nm
spectral range of the incremental ultraviolet mainly responsible
G7 Practice for Natural Weathering of Materials
for the incremental degradation.
G24 Practice for Conducting Exposures to Daylight Filtered
3.2.6.1 Discussion—The definition of this term differs from
Through Glass
that commonly applied to the spectral bandpass, also referred
G90 Practice for Performing Accelerated Outdoor Weather-
to as the spectral bandwidth, of a narrow band filter or the
ing of Materials Using Concentrated Natural Sunlight
radiant energy leaving the exit slit of a monochromator. These
G113 Terminology Relating to Natural and Artificial Weath-
terms are defined as the full width at half-maximum, FWHM,
ering Tests of Nonmetallic Materials
that is, the wavelength range at one half the peak height of the
G147 Practice for Conditioning and Handling of Nonmetal-
spectral band.
lic Materials for Natural and Artificial Weathering Tests
3.2.7 cumulative spectral sensitivity curve, n—a plot of the
G152 Practice for Operating Open Flame Carbon Arc Light
cumulative effect on the optical or physical properties of a
Apparatus for Exposure of Nonmetallic Materials
material of addition of progressively shorter wavelengths of the
G153 Practice for Operating Enclosed Carbon Arc Light
source to the longer wavelength exposure with progressive
Apparatus for Exposure of Nonmetallic Materials
decrease in wavelength of the sharp cut-on UV/visible trans-
G154 Practice for Operating Fluorescent Ultraviolet (UV)
mitting filter.
Lamp Apparatus for Exposure of Materials
G155 Practice for Operating Xenon Arc Lamp Apparatus for
4. Significance and Use
Exposure of Materials
4.1 The activation spectrum identifies the spectral region(s)
3. Terminology
of the specific exposure source used that may be primarily
responsible for changes in appearance and/or physical proper-
3.1 Definitions given in Terminology G113 are applicable to
ties of the material.
this practice.
4.2 The spectrographic technique uses a prism or grating
3.2 Definitions of Terms Specific to This Standard:
spectrograph to determine the effect on the material of isolated
3.2.1 activation spectrum, n—the spectral sensitivity of a
narrow spectral bands of the light source, each in the absence
material specific to the spectral power distribution of the source
of other wavelengths.
to which the material is exposed as a function of a specified
property measurement.
4.3 The sharp cut-on filter technique uses a specially de-
3.2.1.1 Discussion—The activation spectrum of a material
signed set of sharp cut-on UV/visible transmitting glass filters
exhibits peak sensitivity to the spectral region in which the
to determine the relative actinic effects of individual spectral
combination of the radiation intensity, absorption of the radia-
bands of the light source during simultaneous exposure to
tion by the material and quantum efficiency of degradation
wavelengths longer than the spectral band of interest.
produce the maximum damage. Thus, activation spectra show
4.4 Both the spectrographic and filter techniques provide
that many materials exhibit greater damage by wavelengths
activation spectra, but they differ in several respects:
longer than the shortest emitted by the radiation source (see
4.4.1 The spectrographic technique generally provides bet-
Fig. X1.4 and Fig. X1.8). Since activation spectra relate to the
ter resolution since it determines the effects of narrower
spectral emission properties of the radiation source, the acti-
spectral portions of the light source than the filter technique.
vation spectrum varies with the type of radiation source to
4.4.2 The filter technique is more representative of the
which the material is exposed.
polychromatic radiation to which samples are normally ex-
3.2.2 incremental degradation, n—the increase in degrada-
posed with different, and sometimes antagonistic, photochemi-
tion in the specimen exposed behind the shorter wavelength
cal processes often occurring simultaneously. However, since
cut-on filter of the pair due to the addition of short UV
the filters only transmit wavelengths longer than the cut-on
wavelengths transmitted by the filter.
wavelength of each filter, antagonistic processes by wave-
3.2.3 incremental ultraviolet, n—the additional short wave- lengths shorter than the cut-on are eliminated.
length ultraviolet transmitted by the shorter wavelength cut-on 4.4.3 In the filter technique, separate specimens are used to
filter of the pair of sharp cut-on UV/VIS transmitting glass determine the effect of the spectral bands and the specimens are
filters. It is represented by the spectral band (see 3.2.5). sufficiently large for measurement of both mechanical and
G178 − 16 (2023)
optical changes. In the spectrographic technique, except in the 4.6 Over a long test period, the activation spectrum will
case of spectrographs as large as the Okazaki type (1), a single register the effect of the different spectral power distributions
small specimen is used to determine the relative effects of all caused by lamp or filter aging or daily or seasonal variation in
the spectral bands. Thus, property changes are limited to those solar radiation.
that can be measured on very small sections of the specimen.
4.7 In theory, activation spectra may vary with differences
4.5 The information provided by activation spectra on the in sample temperature. However, similar activation spectra
spectral region of the light source responsible for the degrada- have been obtained at ambient temperature (by the spectro-
tion in theory has application to stabilization as well as to graphic technique) and at about 65 °C (by the filter technique)
stability testing of polymeric materials (2). using the same type of radiation source.
4.5.1 Activation spectra based on exposure of the unstabi-
5. Activation Spectrum Procedure Using Sharp Cut-On
lized material to solar radiation identify the light screening
Filter Technique
requirements and thus the type of ultraviolet absorber to use for
optimum screening protection. The closer the match of the
5.1 Spectral Bands of Irradiation:
absorption spectrum of a UV absorber to the activation
5.1.1 Select glass types for the sharp cut-on UV/visible
spectrum of the material, the more effective the screening.
transmitting glass filters which provide a spectral shift of
However, a good match of the UV absorption spectrum of the
approximately 10 nm at 40 % transmittance between filter pairs
UV absorber to the activation spectrum does not necessarily
when ground to appropriate thicknesses. It may be necessary to
assure adequate protection since it is not the only criteria for
use filters from more than one source. The exact thickness to
selecting an effective UV absorber. Factors such as dispersion,
which each filter is ground is governed by the incremental
compatibility, migration and others can have a significant
ultraviolet transmitted by the shorter wavelength filter of the
influence on the effectiveness of a UV absorber (see Note 3).
pair. Adjust the thicknesses so that the incremental ultraviolet
The activation spectrum must be determined using a light
is within 10 % of the average of the incremental ultraviolet of
source that simulates the spectral power distribution of the one
all filter pairs. The method for determining the incremental
to which the material will be exposed under use conditions.
ultraviolet is described in 5.1.3.
NOTE 3—In a study by ASTM G03.01, the activation spectrum of a
NOTE 4—Typically, 12 or 13 filters with cut-on wavelengths ranging
copolyester based on exposure to borosilicate glass-filtered xenon arc
from 265 nm to 375 nm are used to determine the effects of 10 spectral
radiation predicted that UV absorber A would be superior to UV absorber
bands, each approximately 20 nm wide, in the solar UV region. A larger
B in outdoor use because of stronger absorption of the harmful wave-
set of filters can be used to reduce the width of each spectral band, but it
lengths of solar simulated radiation. However, both additives protected the
would extend the time required to produce degradation by each of the
copolyester to the same extent when exposed either to xenon arc radiation
spectral regions. The filter size is normally 2 in. by 2 in., but other sizes
or outdoors.
up to 6 in. by 6 in. can be used.
4.5.2 Comparison of the activation spectrum of the stabi- NOTE 5—The spectral transmittance curves of a typical set of filters are
shown in Figs. X1.1 and X1.2 in the Appendix.
lized with that of the unstabilized material provides informa-
NOTE 6—Due to variations in the melt of each glass type, the filter types
tion on the completeness of screening and identifies any
and thicknesses used for one filter set may not be applicable to o
...
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