ASTM G178-16(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

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

• Status: Published
• Publication Date: 31-Jan-2023
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: G03 - Weathering and Durability
• Drafting Committee: G03.01 - Joint Weathering Projects

Relations

• Refers: ASTM D822-23 - Standard Practice for Filtered Open-Flame Carbon-Arc Exposures of Paint and Related Coatings
• Effective Date: 01-Dec-2023
• Refers: ASTM D5031-23 - Standard Practice for Enclosed Carbon-Arc Exposure Tests of Paint and Related Coatings
• Effective Date: 01-Dec-2023
• Refers: ASTM D2565-23 - Standard Practice for Xenon-Arc Exposure of Plastics Intended for Outdoor Applications
• Effective Date: 01-Oct-2023
• Refers: ASTM G147-17 - Standard Practice for Conditioning and Handling of Nonmetallic Materials for Natural and Artificial Weathering Tests
• Effective Date: 01-Jun-2017
• Refers: ASTM D2244-15a - Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• Effective Date: 01-Aug-2015
• Refers: ASTM D2244-15 - Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• Effective Date: 01-Jan-2015
• Refers: ASTM E313-15 - Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates
• Effective Date: 01-Jan-2015
• Refers: ASTM D2244-15e1 - Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• Effective Date: 01-Jan-2015
• Refers: ASTM D2244-14 - Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• Effective Date: 01-May-2014
• Refers: ASTM G113-14 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 01-Mar-2014
• Refers: ASTM G154-12 - Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials
• Effective Date: 01-Dec-2012
• Refers: ASTM D4587-11 - Standard Practice for Fluorescent UV-Condensation Exposures of Paint and Related Coatings
• Effective Date: 01-Jun-2011
• Refers: ASTM D2244-11 - Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
• Effective Date: 01-Jun-2011
• Refers: ASTM G153-04(2010) - Standard Practice for Operating Enclosed Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials
• Effective Date: 01-Dec-2010
• Refers: ASTM E313-10 - Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates
• Effective Date: 01-Jul-2010

Overview

ASTM G178-16(2023) establishes a standard practice for determining the activation spectrum of a material-specifically, how sensitive a material is to different wavelengths from an exposure source. This is achieved using either sharp cut-on UV/visible transmitting glass filters or a spectrographic technique. By following this procedure, users can identify which portions of the spectrum from artificial or natural light sources most affect the appearance and physical properties of materials such as plastics, paints, inks, and textiles.

This standard is widely referenced in the fields of material durability, accelerated weathering tests, and lightfastness testing of nonmetallic materials. Accurate identification of damaging wavelengths supports improved material stabilization, product development, and performance prediction under environmental stress.

Key Topics

• Activation Spectrum Analysis: Defines the wavelength-dependent sensitivity of a material to a specific exposure source.
• Sharp Cut-On Filter Technique: Utilizes glass filters that transmit only wavelengths longer than their cut-on point, allowing simultaneous exposure to longer wavelengths while isolating the effect of specific spectral bands.
• Spectrographic Technique: Employs a prism or grating spectrograph to expose materials to narrow, isolated spectral bands. This offers higher resolution for analyzing the effects of very specific wavelengths.
• Material Types: Applicable to a diverse range of materials-transparent and opaque-including plastics, coatings, inks, and textiles.
• Test Sources: Techniques are suitable for solar radiation exposures and laboratory accelerated weathering tests, and are applicable in both the UV and visible light regions.
• Comparison of Techniques: The spectrographic method enables finer wavelength discrimination, while the filter method more closely simulates the effects of real-world, polychromatic exposures.
• Data Reporting: The standard outlines detailed requirements for documenting exposure conditions, measurement techniques, and results for both test procedures.

Applications

• Material Durability Testing: Identifies the spectral regions causing the most degradation, guiding the selection of stabilizers or protective additives (e.g., UV absorbers).
• Weathering and Lightfastness Prediction: Essential for industries producing outdoor or light-exposed goods that require long-term color and property retention, such as automotive, construction, textile, and packaging sectors.
• Product Development and Quality Assurance: Helps compare the effectiveness of different stabilizing formulations or coatings under simulated sunlight or artificial UV sources.
• Stability Testing of Polymers and Coatings: Provides data for regulatory and compliance testing, as well as R&D for new materials and formulations.
• Optimization of Accelerated Test Methods: Selects artificial light sources that best mimic the damaging wavelengths found in natural sunlight, leading to more accurate predictions of service life.

Related Standards

• ASTM D256: Test Methods for Determining Impact Resistance of Plastics
• ASTM D638: Test Method for Tensile Properties of Plastics
• ASTM D2244: Practice for Calculation of Color Tolerances from Instrumentally Measured Data
• ASTM D822, D1435, D1499, D2565, D4329, D4364, D4459, D4587: Various practices for accelerated and outdoor exposure of plastics, coatings, and related materials
• ASTM G7, G24, G90, G113, G147, G152, G153, G154, G155: Practices and terminology related to the natural and artificial weathering of nonmetallic materials

Note: There is currently no ISO standard equivalent to ASTM G178-16(2023).

By adhering to ASTM G178-16(2023), laboratories and manufacturers gain a repeatable, internationally recognized method for evaluating material sensitivity to light exposure. This enhances data quality, supports product longevity, and informs the development of more durable and UV-stable products.

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 [e-mail]. 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 other sets.
spectral regions that are not adequately screened.
5.1.2 Spectral Transmittance Data:
4.5.3 Comparison of the activation spectrum of a material
5.1.2.1 Use a UV/visible spectrophotometer that produces
based on solar radiation with those based on exposure to other
either digital data or an analog curve to measure the spectral
types of light sources provides information useful in selection
transmittance of each filter from the spectral region of com-
of the appropriate artificial test source. An adequate match of
plete blocking at the short wavelength end to maximum
the harmful wavelengths of solar radiation by the latter is
transmittance at the long wavelength end.
required to simulate the effects of outdoor exposure. Differ-
ences between the natural and artificial source in the wave- 5.1.2.2 Determine the wavelength calibration and linearity
lengths that cause degradation can result in different mecha- of the spectrophotometer as described in either Practices E275
nisms and type of degradation. or E925. Check the 0 % and 100 % baselines and adjust, if
necessary, according to manufacturer’s recommendations. If
4.5.4 Published data have shown that better correlations can
the 100 % baseline is not flat in the spectral region in which the
be obtained between natural weathering tests under different
filters are measured, correct the data. In the case of analog
seasonal conditions when exposures are timed in terms of solar
curves, use sufficient chart expansion to allow accurate trans-
UV radiant exposure only rather than total solar radiant
mittance values to be read from the chart at 2 nm intervals.
exposure. Timing exposures based on only the portion of the
UV identified by the activation spectrum to be harmful to the 5.1.3 Incremental Ultraviolet:
material can further improve correlations. However, while it is
5.1.3.1 From Digitized Data:
an improvement over the way exposures are currently timed, it
(1) The delta % transmittance for each filter pair and
does not take into consideration the effect of moisture and
resultant spectral bands can often be obtained instrumentally
temperature.
when using a computerized spectrophotometer for the digitized
data.
5.1.3.2 From Analog Data:
(1) Tabulate the % transmittance of each filter at 2 nm
The boldface numbers in parentheses refer to the list of references at the end of
this standard. intervals and calculate the delta % transmittance for each pair
G178 − 16 (2023)
at each wavelength tabulated by subtracting the % transmit- that simulate solar UV spectral irradiance and after a maximum
tance of the longer wavelength cut-on filter from that of the of 2000 h when used for light sources that emit shorter UV
shorter wavelength cut-on filter. wavelengths than solar radiation.
(2) For each filter pair, plot the delta % transmittance
NOTE 12—After more than two years of nearly constant exposure of a
versus wavelength on linear graph paper to produce a spectral
filter set to radiation in a borosilicate glass-filtered (B/B) 6500 watt
curve referred to as the incremental UV. It represents the added
water-cooled xenon arc type exposure device plus several months expo-
portion of the ultraviolet transmitted by the shorter wavelength
sure in a single enclosed carbon arc type exposure device, there was no
detectable change in transmission.
filter of the pair.
5.2.2 Use of the filters with sources of radiation such as the
NOTE 7—Fig. X1.3 is a plot of delta % transmittance from analog data
of the transmittance of filters 5 and 6 shown in Fig. X1.1. quartz-filtered xenon or mercury arcs or the unfiltered open
flame carbon arc is not recommended without prior investiga-
5.1.3.3 Effective Incremental Ultraviolet:
tion of their rates of solarization by these sources.
(1) Determine the areas of the spectral bands above the
5.2.3 It is not necessary to check the full spectral transmis-
delta 10 % transmittance line by any suitable technique,
sion curves of the filters if the transmittance at two wave-
including computerized calculations based on digitized data or
lengths in the region between 10 % and 20 % transmittance has
by use of a planimeter or other technique for curves based on
not changed from the original by more than 1.5 %. If the
analog data. Take the average of at least two measurements by
change is greater than 1.5 %, obtain full spectral curves with
any of the techniques. The areas are used to obtain the
determination of the ultraviolet incremental data of the filter
normalization factors described in 5.1.4.
pairs and normalization factors. If any of the normalization
NOTE 8—Using the area of the spectral band above delta 10 %
factors exceed 15 %, discontinue use of the filter set. Complete
transmittance instead of the full spectral band for the effective incremental
recharacterization of the entire filter set is required following
ultraviolet gives the most meaningful comparison of the incremental
attempts to reverse solarization by heat treatment or other
ultraviolet for all filter pairs. Since some of the spectral bands for the long
wavelength pairs of filters are very broad below the delta 10 % level, means.
inclusion of these areas in the normalization step would require greater
5.2.4 If possible, use the same spectrophotometer for trans-
adjustment of the degradation caused by the shorter wavelengths. It would
mission measurements before and after use since differences in
result in an apparent greater sensitivity of the material to shorter
the band passes of spectrophotometers can alter transmittance
wavelengths.
values in the sharp cut-on spectral region.
5.1.4 Normalization Factors:
5.2.5 Document the exposure history of each filter set,
5.1.4.1 Calculate the normalization factors by dividing the
recording the type of exposure source, its filters, irradiance
average of all the measured areas by the area measured for each
level, exposure time and, if measured, radiant exposure and
filter pair.
spectral region in which it is measured. Document the filter
NOTE 9—Normalization factors are used to adjust the measured
transmission data versus exposure history to determine the
incremental degradation so that it represents the effects of equal spectral
monitoring frequency required. Any attempt at reversing so-
portions of the radiation. Although the filters are designed to provide
larization by heat treatment and its success or failure shall also
nearly equal areas above the delta 10 % transmittance level for all filter
be documented.
pairs, the areas are not identical. This step can be omitted if refinement of
the measured data is not important for the application.
5.2.6 If one or more filters in the set requires replacement
NOTE 10—The normalization factors for the filter set shown in Figs.
because of solarization or damage, replace with a filter that has
X1.1 and X1.2 are given in Fig. X1.7. The areas above 10 % transmittance
the same transmission properties as the original.
were obtained by counting squares of the curves plotted on linear graph
paper.
5.3 Specimens:
5.1.5 Spectral Band Pass:
5.3.1 Number of Spe
...