ASTM G178-03
(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
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 and health practices and determine the applicability of regulatory limitations prior to use.
Note 2-There is no ISO standard that is equivalent to this standard.
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Designation:G178–03
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 G 178; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 256 Test Method for Determining the Izod Pendulum
Impact Resistance of Notched Specimens of Plastics
1.1 This practice describes the determination of the relative
D 638 Test Method for Tensile Properties of Plastics
actinic effects of individual spectral bands of an exposure
D 822 Practice for Filtered Open-Flame Carbon Arc Expo-
source on a material. The activation spectrum is specific to the
sures of Paint and Related Coatings
light source to which the material is exposed to obtain the
D 1435 Practice for Outdoor Weathering of Plastics
activation spectrum. A light source with a different spectral
D 1499 Practice for Operating Light- and Water-Exposure
powerdistributionwillproduceadifferentactivationspectrum.
Apparatus (Carbon Arc Type) for Exposure of Plastics
1.2 This practice describes two procedures for determining
D 2244 Test Method for Calculation of Color Differences
an activation spectrum. One uses sharp cut-on UV/visible
from Instrumentally Measured Color Coordinates
transmitting filters and the other uses a spectrograph to
D 2565 Practice for Operating Xenon Arc Type Light Ex-
determine the relative degradation caused by individual spec-
posureApparatus With and Without Water for Exposure of
tral regions.
Plastics
NOTE 1—Other techniques can be used to isolate the effects of
D 4141 Practice for ConductingAccelerated Outdoor Expo-
individual spectral bands of a light source, for example, interference
sure Tests of Coatings
filters.
D 4329 Practice for Operating Light- and Water-Exposure
1.3 The techniques are applicable to determination of the
Apparatus (Fluorescent UV Condensation Type) for Expo-
spectral effects of solar radiation and laboratory accelerated
sure of Plastics
test devices on a material. They are described for the UV
D 4364 Practice for Performing Accelerated Outdoor
region, but can be extended into the visible region using
Weathering of Plastics Using Concentrated Natural Sun-
different cut-on filters and appropriate spectrographs. 5
light
1.4 The techniques are applicable to a variety of materials,
D 4459 Practice for Operating anAccelerated Lightfastness
both transparent and opaque, including plastics, paints, inks,
Xenon Arc Type Light Exposure Apparatus for the Expo-
textiles and others.
sure of Plastics for Indoor Applications
1.5 The optical and/or physical property changes in a 5
D 4508 Test Method for Chip Impact Strength of Plastics
material can be determined by various appropriate methods.
D 4587 Practice for Fluorescent UV-Condensation Expo-
The methods of evaluation are beyond the scope of this 3
sures of Paint and Related Coatings
practice.
D 5031 Practice for Enclosed CarbonArc ExposureTests of
1.6 This standard does not purport to address all of the 3
Paint and Related Coatings
safety concerns, if any, associated with its use. It is the
D 6360 Practice for Enclosed Carbon-Arc Exposures of
responsibility of the user of this standard to establish appro- 4
Plastics
priate safety and health practices and determine the applica-
D 6695 Practice for Xenon-Arc Exposures of Paint and
bility of regulatory limitations prior to use.
Related Coatings
E 275 Practice for Describing and Measuring Performance
NOTE 2—There is no ISO standard that is equivalent to this standard.
of Ultraviolet, Visible and Near Infrared Spectrophotom-
2. Referenced Documents
eters
2.1 ASTM Standards:
Annual Book of ASTM Standards, Vol 08.01.
1 3
This practice is under the jurisdiction ofASTM Committee G03 onWeathering Annual Book of ASTM Standards, Vol 06.01.
and Durability and is the direct responsibility of Subcommittee G03.01 on Joint Annual Book of ASTM Standards, Vol 08.02.
Weathering Projects. Annual Book of ASTM Standards, Vol 08.03.
Current edition approved July 10, 2003. Published September 2003. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G178–03
E 313 Test Method for Indexes of Whiteness and Yellow- terms are defined as the full width at half-maximum, FWHM,
ness of Near-White Opaque Materials that is, the wavelength range at one half the peak height of the
spectral band.
E 925 Practice for Periodic Calibration for Narrow Band-
Pass Spectrophotometers 3.2.6 cumulative spectral sensitivity curve, n—a plot of the
cumulative effect on the optical or physical properties of a
G 7 Practice for Atmospheric Environmental Exposure
materialofadditionofprogressivelyshorterwavelengthsofthe
Testing of Nonmetallic Materials
source to the longer wavelength exposure with progressive
G 24 Practice for Conducting Exposures to Daylight Fil-
decrease in wavelength of the sharp cut-on UV/visible trans-
tered Through Glass
mitting filter.
G 90 Practice for Performing Accelerated Outdoor Weath-
ering of Nonmetallic Materials Using Concentrated Natu-
7 4. Significance and Use
ral Sunlight
4.1 The activation spectrum identifies the spectral region(s)
G 113 Terminology Relating to Natural and Artificial
of the specific exposure source used that may be primarily
Weathering Tests of Nonmetallic Materials
responsible for changes in appearance and/or physical proper-
G 147 Practice for Conditioning and Handling of Nonme-
ties of the material.
tallicMaterialsforNaturalandArtificialWeatheringTests
4.2 The spectrographic technique uses a prism or grating
G 152 PracticeforOperatingOpenFlameCarbonArcLight
spectrograph to determine the effect on the material of isolated
Apparatus for Exposure of Nonmetallic Materials
narrow spectral bands of the light source, each in the absence
G 153 Practice for Operating Enclosed Carbon Arc Light
7 of other wavelengths.
Apparatus for Exposure of Nonmetallic Materials
4.3 The sharp cut-on filter technique uses a specially de-
G 154 Practice for Operating Fluorescent Light Apparatus
signed set of sharp cut-on UV/visible transmitting glass filters
for UV Exposure of Nonmetallic Materials
to determine the relative actinic effects of individual spectral
G 155 Practice for Operating Xenon Arc Light Apparatus
bands of the light source during simultaneous exposure to
for Exposure of Nonmetallic Materials
wavelengths longer than the spectral band of interest.
4.4 Both the spectrographic and filter techniques provide
3. Terminology
activation spectra, but they differ in several respects:
3.1 Definitions given in Terminology G 113 are applicable
4.4.1 The spectrographic technique generally provides bet-
to this practice.
ter resolution since it determines the effects of narrower
3.2 Definitions of Terms Specific to This Standard:
spectral portions of the light source than the filter technique.
3.2.1 incremental degradation, n— the increase in degrada-
4.4.2 The filter technique is more representative of the
tion in the specimen exposed behind the shorter wavelength
polychromatic radiation to which samples are normally ex-
cut-on filter of the pair due to the addition of short UV
posed with different, and sometimes antagonistic, photochemi-
wavelengths transmitted by the filter.
cal processes often occurring simultaneously. However, since
3.2.2 incremental ultraviolet, n—the additional short wave-
the filters only transmit wavelengths longer than the cut-on
length ultraviolet transmitted by the shorter wavelength cut-on
wavelength of each filter, antagonistic processes by wave-
filter of the pair of sharp cut-on UV/VIS transmitting glass
lengths shorter than the cut-on are eliminated.
filters. It is represented by the spectral band (see 3.2.4).
4.4.3 In the filter technique, separate specimens are used to
3.2.3 sharp cut-on UV/VIS transmitting glass filters,
determinetheeffectofthespectralbandsandthespecimensare
n—filters that screen out the short wavelengths and transmit
sufficiently large for measurement of both mechanical and
radiation longer than the cut-on wavelength. The transmittance
optical changes. In the spectrographic technique, except in the
increases sharply from 5 %, the cut-on wavelength, to 72 %
caseofspectrographsaslargeastheOkazakitype(1), asingle
within a spectral range of about 20 nm. They are also referred
small specimen is used to determine the relative effects of all
to as longpass filters.
the spectral bands. Thus, property changes are limited to those
3.2.4 spectral band, n—the spectral region defined by the that can be measured on very small sections of the specimen.
difference in transmittance of a pair of the sharp cut-on
4.5 The information provided by activation spectra on the
UV/VIS transmitting glass filters. It is also referred to as the spectral region of the light source responsible for the degrada-
incremental ultraviolet.
tion in theory has application to stabilization as well as to
3.2.5 spectral band pass, n—the spectral range of the stability testing of polymeric materials (2).
spectral band at the delta 20 % transmittance level. It is the 4.5.1 Activation spectra based on exposure of the unstabi-
spectral range of the incremental ultraviolet mainly responsible lized material to solar radiation identify the light screening
for the incremental degradation. requirementsandthusthetypeofultravioletabsorbertousefor
optimum screening protection. The closer the match of the
3.2.5.1 Discussion—The definition of this term differs from
that commonly applied to the spectral bandpass, also referred absorption spectrum of a UV absorber to the activation
spectrum of the material, the more effective the screening .The
to as the spectral bandwidth, of a narrow band filter or the
radiant energy leaving the exit slit of a monochromator. These activation spectrum must be determined using a light source
The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 14.02. this standard.
G178–03
that simulates the spectral power distribution of the one to pair. Adjust the thicknesses so that the incremental ultraviolet
which the material will be exposed under use conditions. is within 10 % of the average of the incremental ultraviolet of
However, a good match of the UV absorption spectrum of the all filter pairs. The method for determining the incremental
UV absorber to the activation spectrum does not necessarily ultraviolet is described in 5.1.3.
assure adequate protection since it is not the only criteria for
NOTE 4—Typically, 12 or 13 filters with cut-on wavelengths ranging
selecting an effective UV absorber. Factors such as dispersion,
from 265 to 375 nm are used to determine the effects of 10 spectral bands,
compatibility, migration and others can have a significant
each approximately 20 nm wide, in the solar UV region. A larger set of
influence on the effectiveness of a UV absorber (see Note 3). filters can be used to reduce the width of each spectral band, but it would
extend the time required to produce degradation by each of the spectral
NOTE 3—In a study by ASTM G03.01, the activation spectrum of a
regions. The filter size is normally 2 by 2 in., but other sizes up to 6 by 6
copolyester based on exposure to borosilicate glass-filtered xenon arc
in. can be used.
radiation predicted that UV absorberAwould be superior to UV absorber
NOTE 5—The spectral transmittance curves of a typical set of filters are
B in outdoor use because of stronger absorption of the harmful wave-
shown in Figs. X1.1 and X1.2 in the Appendix.
lengthsofsolarsimulatedradiation.However,bothadditivesprotectedthe
NOTE 6—Duetovariationsinthemeltofeachglasstype,thefiltertypes
copolyester to the same extent when exposed either to xenon arc radiation
and thicknesses used for one filter set may not be applicable to other sets.
oroutdoors.Aresearchreportonthestudyandinterpretationoftestresults
is being written.
5.1.2 Spectral Transmittance Data:
4.5.2 Comparison of the activation spectrum of the stabi- 5.1.2.1 Use a UV/visible spectrophotometer that produces
lized with that of the unstabilized material provides informa- either digital data or an analog curve to measure the spectral
tion on the completeness of screening and identifies any transmittance of each filter from the spectral region of com-
spectral regions that are not adequately screened. plete blocking at the short wavelength end to maximum
4.5.3 Comparison of the activation spectrum of a material transmittance at the long wavelength end.
based on solar radiation with those based on exposure to other 5.1.2.2 Determine the wavelength calibration and linearity
of the spectrophotometer as described in either Practice E 275
types of light sources provides information useful in selection
of the appropriate artificial test source. An adequate match of or E 925. Check the 0 % and 100 % baselines and adjust, if
necessary, according to manufacturer’s recommendations. If
the harmful wavelengths of solar radiation by the latter is
required to simulate the effects of outdoor exposure. Differ- the100 %baselineisnotflatinthespectralregioninwhichthe
filters are measured, correct the data. In the case of analog
ences between the natural and artificial source in the wave-
lengths that cause degradation can result in different mecha- curves, use sufficient chart expansion to allow accurate trans-
mittance values to be read from the chart at 2 nm intervals.
nisms and type of degradation.
4.5.4 Published data have shown that better correlations can 5.1.3 Incremental Ultraviolet:
5.1.3.1 From Digitized Data:
be obtained between natural weathering tests under different
seasonal conditions when exposures are timed in terms of solar (1) The delta % transmittance for each filter pair and
resultant spectral bands can often be obtained instrumentally
UV radiant exposure only rather than total solar radiant
exposure. Timing exposures based on only the portion of the when using a computerized spectrophotometer for the digitized
UV identified by the activation spectrum to be harmful to the data.
material can further improve correlations. However, while it is 5.1.3.2 From Analog Data:
an improvement over the way exposures are currently timed, it (1) Tabulate the % transmittance of each filter at 2 nm
does not take into consideration the effect of moisture and intervals and calcu
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