ASTM D4674-19

Standard Practice for Accelerated Testing for Color Stability of Plastics Exposed to Indoor Office Environments

SIGNIFICANCE AND USE
5.1 Tests conducted in accordance with this practice are intended to induce property changes associated with use exposure to light and heat in typical office environments. These exposures are not intended to simulate the deterioration caused by localized phenomena such as handling, dirt contamination, etc.
Note 5: Caution: Refer to practice G151 for full cautionary guidance applicable to all laboratory weathering devices. Additional information on sources of variability and on strategies for addressing variability by design and data analysis of laboratory accelerated exposure tests is found in Guide G141.  
5.2 Variation in results may be expected are possible between the different methods described in this practice. For example, differences in spectral distribution of the lamps used and variations in the irradiance for a single type of lamp can cause significant differences in test results. Therefore, any no reference to the use of this practice should be made unless accompanied by a report prepared in accordance with Section 12 that describes needs to include a reference to the method used.  
5.3 Reproducibility of test results between laboratories has been shown to be good when the stability of materials is evaluated in terms of performance ranking compared to other materials or to a control. Therefore, exposure of a similar material of known performance (a control) at the same time as the test materials is strongly recommended. It is recommended that at least three replicates of each material be exposed to allow for statistical evaluation of results.
SCOPE
1.1 This practice covers the basic principles and operating procedures for using fluorescent light to determine color stability of plastics when materials are exposed in typical office environments where fluorescent overhead lighting and window-filtered daylight are used for illumination and where temperature and humidity conditions are in accordance with American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) recommendations for workers' comfort.  
1.2 This practice describes four methods where specimens are exposed to fluorescent light under controlled environmental conditions. Two of the methods use an exposure device that provides for mixing of fluorescent lamps and two of the methods use devices that comply with Practice G154.
Note 1: Method I uses cool white fluorescent lamps and window glass filtered fluorescent UVB lamps and is the same method described in previous versions of this standard.  
1.3 Specimen preparation and evaluation of the results are covered in ASTM methods or specifications for specific materials. General guidance is given in Practice G151. More specific information about methods for determining the change in properties after exposure and reporting these results is described in Practice D5870.  
1.4 The values stated in SI units are to be regarded as the standard.  
1.5 Unless otherwise specified, all dimensions are nominal.  
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. Specific precautionary statements are given in Section 7.
Note 2: There is no known ISO 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 Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Apr-2019
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.50 - Durability of Plastics

Relations

• Replaces: ASTM D4674-02a(2010) - Standard Practice for Accelerated Testing for Color Stability of Plastics Exposed to Indoor Office Environments (Withdrawn 2019)
• Effective Date: 15-Apr-2019
• 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 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 E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• 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 E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-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 D5870-11 - Standard Practice for Calculating Property Retention Index of Plastics
• Effective Date: 01-Feb-2011
• Refers: ASTM G151-10 - Standard Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light Sources
• Effective Date: 01-Apr-2010
• Refers: ASTM G141-09 - Standard Guide for Addressing Variability in Exposure Testing on Nonmetallic Materials
• Effective Date: 01-Dec-2009
• Refers: ASTM D1729-96(2009) - Standard Practice for Visual Appraisal of Colors and Color Differences of Diffusely-Illuminated Opaque Materials
• Effective Date: 01-Dec-2009

Overview

ASTM D4674-19 is the industry standard for accelerated testing of color stability in plastics exposed to indoor office environments. Developed by ASTM International, this practice specifies the use of fluorescent lighting to simulate typical indoor conditions, allowing manufacturers and researchers to assess the color durability of plastics over time. The standard is foundational in evaluating the resistance of plastic materials to light- and heat-induced changes under realistic office conditions featuring fluorescent overhead lighting and daylight filtered by windows, and under temperature and humidity levels consistent with ASHRAE recommendations.

This practice is particularly important for quality control, product development, and comparative evaluations where long-term color stability is critical, such as in office furnishings, equipment housings, and building materials.

Key Topics

• Accelerated Exposure Methods: Describes four primary exposure methods using combinations of cool white and filtered UV fluorescent lamps, simulating both office lighting and sunlight through windows.
• Test Chamber Requirements: Specifications for test chamber design, lighting, temperature, humidity control, and lamp types to ensure standardized testing conditions.
• Specimen Preparation and Evaluation: Outlines best practices for specimen preparation, mounting, and evaluation of color changes, including the recommendation for at least three replicates and the use of a known performance control material for comparative analysis.
• Data Reporting and Analysis: Emphasizes comprehensive documentation of test conditions, exposure methods, lamp details, exposure duration, and evaluation procedures in accordance with Section 12 of the standard.
• Reproducibility and Variability: Discusses factors affecting reproducibility between laboratories, such as spectral distribution, irradiance variation, and the importance of statistical evaluation.
• Safety and Best Practices: Stresses adherence to safety protocols, calibration requirements, and environmental recommendations for reliable results.

Applications

The practical value of ASTM D4674 lies in its ability to:

• Predict Long-Term Performance: Manufacturers use these accelerated methods to estimate how plastics will hold up to years of indoor office light exposure, helping guide material selection and product design.
• Quality Assurance: Regular use of this standard supports consistent product quality by verifying the color stability of production batches.
• Regulatory and Specification Compliance: Provides a recognized benchmark for clients or regulatory bodies that require evidence of colorfastness for plastics intended for office environments.
• Comparative Material Evaluation: Enables direct comparison of new formulations, additives, or suppliers by testing under standardized conditions.
• Product Development: Allows R&D teams to rapidly screen materials and optimize formulations for improved indoor light stability.

Industries benefitting from ASTM D4674 include office furniture, electronics, lighting fixtures, building construction, and any application where plastics are exposed to indoor light over prolonged periods. This testing practice ensures that end products maintain their intended aesthetic and performance throughout their lifecycle in office environments.

Related Standards

• ASTM G151: General guidance for exposing nonmetallic materials in accelerated test devices using laboratory light sources, including safety and variability considerations.
• ASTM G154: Specific procedures for operating fluorescent ultraviolet (UV) lamp apparatus for exposing nonmetallic materials.
• ASTM D1729: Practice for visual appraisal of colors and color differences.
• ASTM D2244: Calculation of color tolerances and color differences from instrumentally measured color coordinates.
• ASTM D5870: Methods for calculating the property retention index of plastics after exposure.
• ASTM G141 & G169: Strategies to address variability and statistical methods relevant to weathering and exposure tests.

Note: There is currently no ISO equivalent to ASTM D4674, making this the primary reference for testing color stability of plastics in indoor office environments.

---

Keywords: ASTM D4674, color stability, plastics, indoor office environments, accelerated testing, fluorescent light exposure, colorfastness, office furniture plastics, ASTM International, product performance, quality assurance, laboratory exposure testing.

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: D4674 − 19
Standard Practice for
Accelerated Testing for Color Stability of Plastics Exposed
to Indoor Office Environments
This standard is issued under the fixed designation D4674; 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 covers the basic principles and operating
ization established in the Decision on Principles for the
procedures for using fluorescent light to determine color
Development of International Standards, Guides and Recom-
stabilityofplasticswhenmaterialsareexposedintypicaloffice
mendations issued by the World Trade Organization Technical
environments where fluorescent overhead lighting and
Barriers to Trade (TBT) Committee.
window-filtered daylight are used for illumination and where
temperature and humidity conditions are in accordance with
2. Referenced Documents
American Society of Heating, Refrigerating, and Air-
2.1 ASTM Standards:
conditioning Engineers (ASHRAE) recommendations for
D1729 Practice for Visual Appraisal of Colors and Color
workers’ comfort.
Differences of Diffusely-Illuminated Opaque Materials
1.2 This practice describes four methods where specimens
D2244 Practice for Calculation of Color Tolerances and
areexposedtofluorescentlightundercontrolledenvironmental
Color Differences from Instrumentally Measured Color
conditions. Two of the methods use an exposure device that
Coordinates
provides for mixing of fluorescent lamps and two of the
D3980 Practice for Interlaboratory Testing of Paint and
methods use devices that comply with Practice G154.
Related Materials (Withdrawn 1998)
NOTE 1—Method I uses cool white fluorescent lamps and window glass D5870 Practice for Calculating Property Retention Index of
filtered fluorescent UVB lamps and is the same method described in
Plastics
previous versions of this standard.
E691 Practice for Conducting an Interlaboratory Study to
1.3 Specimen preparation and evaluation of the results are
Determine the Precision of a Test Method
covered in ASTM methods or specifications for specific
G113 Terminology Relating to Natural andArtificial Weath-
materials. General guidance is given in Practice G151. More
ering Tests of Nonmetallic Materials
specific information about methods for determining the change
G141 Guide for Addressing Variability in Exposure Testing
in properties after exposure and reporting these results is
of Nonmetallic Materials
described in Practice D5870.
G147 Practice for Conditioning and Handling of Nonmetal-
lic Materials for Natural and Artificial Weathering Tests
1.4 The values stated in SI units are to be regarded as the
G151 Practice for Exposing Nonmetallic Materials inAccel-
standard.
erated Test Devices that Use Laboratory Light Sources
1.5 Unless otherwise specified, all dimensions are nominal.
G154 Practice for Operating Fluorescent Ultraviolet (UV)
1.6 This standard does not purport to address all of the
Lamp Apparatus for Exposure of Nonmetallic Materials
safety concerns, if any, associated with its use. It is the
G169 Guide for Application of Basic Statistical Methods to
responsibility of the user of this standard to establish appro-
Weathering Tests
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
Specific precautionary statements are given in Section 7.
3.1 Definitions—ThedefinitionsgiveninTerminologyG113
are applicable to this practice.
NOTE 2—There is no known ISO equivalent to this standard.
1 2
ThispracticeisunderthejurisdictionofASTMCommitteeD20onPlasticsand For referenced ASTM standards, visit the ASTM website, www.astm.org, or
is the direct responsibility of Subcommittee D20.50 on Durability of Plastics. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved April 15, 2019. Published May 2019. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1987. Last previous edition approved in 2010 as D4674 - 02a(2010), the ASTM website.
which was withdrawn January 2019 and reinstated in April 2019. DOI: 10.1520/ The last approved version of this historical standard is referenced on
D4674-19. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4674 − 19
4. Summary of Practice that at least three replicates of each material be exposed to
allow for statistical evaluation of results.
4.1 This practice provides for the exposure of specimens to
fluorescent light under controlled environmental conditions.
6. Apparatus
Radiant energy is provided by one of the following fluorescent
light sources: (1) VHO cool-white fluorescent lamps and glass
6.1 Test Chamber—Unless otherwise specified, the test
filtered fluorescent UV lamps, (2) VHO cool-white fluorescent
chamber shall comply with the requirements of Practice G151.
lamps alone, (3) standard output cool white fluorescent lamps
6.1.1 The test chamber used for Methods I and II shall be
alone, or (4) UVA-351 fluorescent UVA lamps.
designed so that simultaneous operation of VHO cool white
4.1.1 Method I is intended to simulate the conditions in an
andglassfilteredUVfluorescentlampsispossible,andshallbe
office environment plus a portion of solar UV radiation
equipped with a radiometer complying with the requirements
transmitted by window glass. Methods II and III are intended
of Practice G151 and calibrated from 250 to 400 nm. Annex
to simulate only the indoor lighting component of a typical
Annex A1 contains more information about the design of the
office environment. Method IVis intended to simulate only the
apparatus used for Methods I and II.
effects of a portion of solar UV radiation transmitted through
6.1.2 The test chamber used for Methods III and IV shall
window glass.
conform to the requirements of Practice G154.
NOTE 3—A comparison of the four listed methods has not been
6.2 The spectral distribution of the UVB-313, UVA-340,
performed, and as such, results obtained from each method cannot be
and UVA-351 shall comply with the requirements of practice
considered as equivalent.
G154. The spectral power distribution of the cool white lamps
NOTE 4—For more information on the use of fluorescent UV lamps to
usedshallcomplywiththerequirementsgiveninAnnexAnnex
simulate solar UV radiation behind window glass, refer to Annex A1 of
Practice G154. A2.
4.1.2 Do not compare Comparison of results obtained from
6.3 Window glass—Unless otherwise specified the window
specimens exposed using the methods described should not be
glass shall be good grade clear, flat, drawn “single strength”
made unless correlation has been established between the sheet glass free of bubbles or other imperfections and between
methods being compared for the materials being tested.
2.0 and 2.5 mm in thickness. The glass shall be preaged in the
device for at least 24 hours prior to use.
4.2 Color change is determined periodically throughout the
course of the exposure by comparison of the exposed speci-
6.4 For Methods I and II, place the apparatus in an envi-
mens to unexposed specimens, using either visual or instru-
ronment that meets ASHRAE recommendations of 20 to
mental procedures.
25.5°C and 40 to 50 % relative humidity. For Methods III and
IV follow the requirements of Practice G154 for the area in
5. Significance and Use
which the instruments are used.
5.1 Tests conducted in accordance with this practice are
6.5 Instrument Calibration—To ensure standardization and
intended to induce property changes associated with use
accuracy, the instruments associated with the exposure appa-
exposuretolightandheatintypicalofficeenvironments.These
ratus (for example, timers, thermometers, UV sensors, and
exposures are not intended to simulate the deterioration caused
radiometers)requireperiodiccalibrationtoensurerepeatability
by localized phenomena such as handling, dirt contamination,
of test results. Whenever possible, calibration should needs to
etc.
be traceable to national or international standards. Unless
otherwise specified, calibration schedule and procedure shall
NOTE 5—Caution: Refer to practice G151 for full cautionary guidance
be in accordance with manufacturer’s instructions.
applicable to all laboratory weathering devices.Additional information on
sourcesofvariabilityandonstrategiesforaddressingvariabilitybydesign
and data analysis of laboratory accelerated exposure tests is found in
7. Hazards
Guide G141.
7.1 Never look directly at the operating lamps unless
5.2 Variation in results may be expected are possible be-
wearing UV protective eyewear. The apparatus specified in
tween the different methods described in this practice. For
Section 6 shall be constructed so that the operator will not be
example, differences in spectral distribution of the lamps used
exposed to hazardous levels of UV radiation.
and variations in the irradiance for a single type of lamp can
7.2 Discard or recycle lamps in accordance with any rel-
cause significant differences in test results. Therefore, any no
evant local ordinances when they are no longer suitable for the
reference to the use of this practice should be made unless
tests described.
accompanied by a report prepared in accordance with Section
12 that describes needs to include a reference to the method
8. Test Specimens
used.
5.3 Reproducibility of test results between laboratories has 8.1 The recommended specimen size is a rectangular flat
been shown to be good when the stability of materials is piece 50 by 80 by 4 mm (minimum thickness). This size is
evaluated in terms of performance ranking compared to other adequate for visual or instrumental evaluation. Other specimen
materials or to a control. Therefore, exposure of a similar dimensions may be used by mutual agreement among the
material of known performance (a control) at the same time as parties concerned but exposed surfaces need to be coplanar for
the test materials is strongly recommended. It is recommended most consistent results.
D4674 − 19
9. Test Conditions (1) Replace the cool white lamps if UV is greater than
OFF
or equal to one.
9.1 Conduct exposures in accordance with one of the
following exposure methods.
9.1.1.7 Program the device so that the cool white lamps
9.1.1 Method I:
operate continuously and the fluorescent UV lamps are turned
9.1.1.1 Use apparatus conforming to the requirements de- on once per hour for the fraction of time calculated in section
scribed in Annex Annex A1.
9.1.1.6. Continue the exposure for the total time calculated in
section 9.1.1.4.
NOTE 6—For Method I, the contribution of fluorescent UV lamp
9.1.1.8 Reposition the specimens at time intervals equal to
radiation to the total UV actinic exposure is adjusted by changing the
percentage of time the specimens are exposed to the various lamp types. 25 6 5 % of the total time calculated in section 9.1.1.4. Move
specimens just to the right of the center line of the exposure
9.1.1.2 This method provides for exposure of specimens to
areatothepositionfarthesttotherightintheexposureareaand
radiant energy from an array of very high output (VHO) cool
move remaining specimens one position to the left. Move
white fluorescent lamps plus intermittent radiant energy from
specimens just to the left of the center line of the exposure to
window glass filtered fluorescent UV lamps. The total UV
the position farthest to the left in the exposure area and move
radiant exposure from both sources is calculated by determin-
remaining specimens in this half one position to the right.
ing the total UV irradiance from each type of lamp separately
9.1.1.9 Maintain chamber air temperature between 30 and
and calculating the product of the total UV irradiance and
2 2
40°C during the exposure. If the air temperature exceeds 40°C,
exposure time in Watt-hours/m (W-h/m ).
the device must be shut off and the cause for the high
9.1.1.3 Place test specimens in the exposure area, leaving at
temperature corrected before exposures can continue.
least a 25 mm empty border around the exposure area.
9.1.1.10 Conduct exposures for a total time agreed upon by
9.1.1.4 Run the device with both the cool white and fluo-
all interested parties. Periodically remove test and control
rescent UV lamps on for at least 20 minutes, then turn off the
specimens for color measurement and relevant physical prop-
fluorescent UV lamps and record the UV irradiance with only
erty tests.
the cool white lamps operating (CWE in W/m , 250-400 nm).
9.1.2 Method II:
Calculate the exposure time required for the desired CW
E
radiant exposure as follows:
9.1.2.1 Use apparatus conforming to the requirements of
Annex A, but without the fluorescent UV lamps.
CW
H
CW 5 (1)
t
9.1.2.2 Place test specimens in the exposure area, leaving at
CW
E
least a 25 mm empty border around the exposure area.
where:
9.1.2.3 Operate the device for at least 20 minutes then
CW = exposure time for cool white lamps,
t
record the UV irradiance (CW ,in W/m , 250-400 nm).
UV
CW = desired UV radiant exposure for cool white lamps
H
Calculate the exposure time necessary for the desired cool
alone, and
white UV irradiance exposure in accordance with section
CW = UV irradiance measured with only with the cool
E
9.1.1.4.
white lamps operating.
9.1.2.4 Reposition the specimens during the exposure as
9.1.1.5 Run the device with only the fluorescent UV lamps
described in section 9.1.1.8.
on and record the UVirradiance (UVE inW/m , 250-400 nm).
9.1.2.5 Maintain chamber air temperature between 30 and
The UV actinic exposure from the filtered fluorescent UV
40°C during the exposure. If the air temperature exceeds 40°C,
lamps is set at 12 % of the UV actinic exposure for the cool
the device must be shut off and the cause for the high
white lamps. Calculate the total operating time for the fluores-
temperature corrected before exposures can continue.
cent UV lamps as follows:
9.1.2.6 Conduct exposures for a total time agreed upon by
0.12 3CW
H
all interested parties. Periodically remove test and control
UV 5 (2)
t
UV
E
specimens for color measurement and relevant physical prop-
erty tests.
where:
9.1.3 Method III:
UV = exposure time for fluorescent UV lamps,
t
CW = desired UV radiant exposure for cool white lamps 9.1.3.1 Use apparatus conforming to the requirements of
H
alone, and Practice G154 and equipped with F40T12 cool white lamps.
UV = UV irradiance measured with only with the fluores-
Place specimens in the devices, and fill all spaces not used by
E
cent UV lamps operating. test specimens with blank metal panels. Operate the device
NOTE 7—Although an office environment sees some UV exposure due with lamps on continuously and with the black panel tempera-
to sunlight through window glass, most photodegradation originates from
ture controlled at 50 6 3°C.
fluorescent lighting. The 12 % is an estimate of a representative office
9.1.3.2 Specimen Repositioning—Periodic repositioning of
environment.
the specimens during exposure is not necessary if the irradi-
9.1.1.6 Calculate the fraction of time per hour for which the
ance at the positions farthest from the center of the specimen
fluorescent UV lamps are turned off (UV ) as follows:
OFF
area is at least 90 % of that measured at the center of the
CW 2 UV
exposure area. Irradiance uniformity shall be determined in
t t
UV 5 (3)
OFF
UV accordance with Practice G151.
t
D4674 − 19
9.1.3.3 Conduct exposures for a total time agreed upon by coverforthepurposeofshowingtheeffectsofexposureonone
all interested parties. Periodically remove test and control panel. Misleading results may be obtained by using this
specimens for color measurement and relevant physical prop- method, since the masked portion of the specimen is still
erty tests. exposed to temperature and humidity that in many cases will
9.1.4 Method IV: affect results.
9.1.4.1 Use apparatus conforming to the requirements of
10.6 Exposure to Test Conditions—Unless otherwise
Practice G154 and equipped with UVA351 lamps that comply
specified, expose specimens in accordance with one of the
withtherequirementsofPracticeG154.Placespecimensinthe
methods described in Section 9. Maintain these conditions
devices, and fill all spaces not used by test specimens with
throughout the exposure. Interruptions to service the apparatus
blank metal panels. Operate the device with lamps on continu-
and to inspect specimens shall be minimized.
ously and with the black panel temperature controlled at
10.7 Inspection—Ifitisnecessarytoremoveatestspecimen
50 6 3°C.
for periodic inspection, take care not to handle or disturb the
9.1.4.2 Specimen Repositioning—Periodic repositioning of
test surface. After inspection, the test specimen shall be
the specimens during exposure is not necessary if the irradi-
returned to the test chamber with its test surface in the same
ance at the positions farthest from the center of the specimen
orientation as previously tested.
area is at least 90 % of that measured at the center of the
10.8 Apparatus Maintenance—The test apparatus requires
exposure area. Irradiance uniformity shall be determined in
accordance with Practice G151. periodicm
...