ASTM G207-11(2019)e1

Standard Test Method for Indoor Transfer of Calibration from Reference to Field Pyranometers

SIGNIFICANCE AND USE
5.1 The methods described represent a means for calibration of field radiometers employing standard reference radiometers indoors. Other methods involve the natural sunlight outdoors under clear skies, and various combinations of reference radiometers. Outdoors, these methods are useful for cosine and azimuth correction analyses but may suffer from a lack of available clear skies, foreground view factor and directionality problems. Outdoor transfer of calibrations is covered by standards G167, E816, and E824.  
5.2 Several configurations of artificial sources are possible, including:  
5.2.1 Point sources (lamps) at a distance, to which the sensors are exposed.  
5.2.2 Extended sources (banks of lamps, or lamp(s) behind diffusing or “homogenizing” screens) to which the sensors are exposed.  
5.2.3 Various configurations of enclosures (usually spherical or hemispherical) with the interior walls illuminated indirectly with lamps. The sensors are exposed to the radiation emanating from the enclosure walls.  
5.3 Traceability of calibration for pyranometers is accomplished when employing the method using a reference global pyranometer that has been calibrated and is traceable to the World Radiometric Reference (WRR).4 For the purposes of this test method, traceability shall have been established if a parent instrument in the calibration chain can be traced to a reference pyrheliometer which has participated in an International Pyrheliometric Comparison (IPC) conducted at the World Radiation Center, (WRC), Davos, Switzerland.  
5.3.1 The reference global pyranometer (for example, one measuring hemispherical solar radiation at all wavelengths) shall have been calibrated by the shading-disk, component summation, or outdoor comparison method against one of the following instruments:
5.3.1.1 An absolute cavity pyrheliometer that participated in a World Meteorological Organization (WMO) sanctioned IPC's (and therefore possesses a WRR reduction factor).
5.3.1.2 An a...
SCOPE
1.1 The method described in this standard applies to the indoor transfer of calibration from reference to field radiometers to be used for measuring and monitoring outdoor radiant exposure levels.  
1.2 This test method is applicable to field radiometers regardless of the radiation receptor employed but is limited to radiometers having approximately 180° (2π Steradian), field angles.  
1.3 The calibration covered by this test method employs the use of artificial light sources (lamps).  
1.4 Calibrations of field radiometers are performed with sensors horizontal (at 0° tilt from the horizontal to the earth). The essential requirement is that the reference radiometer shall have been calibrated at horizontal tilt as employed in the transfer of calibration.  
1.5 The primary reference instrument shall not be used as a field instrument and its exposure to sunlight shall be limited to outdoor calibration or intercomparisons.
Note 1: At a laboratory where calibrations are performed regularly it is advisable to maintain a group of two or three reference radiometers that are included in every calibration. These serve as controls to detect any instability or irregularity in the standard reference instrument.  
1.6 Reference standard instruments shall be stored in a manner as to not degrade their calibration.  
1.7 The method of calibration specified for total solar pyranometers shall be traceable to the World Radiometric Reference (WRR) through the calibration methods of the reference standard instruments (Method G167 and Test Method E816), and the method of calibration specified for narrow- and broad-band ultraviolet radiometers shall be traceable to the National Institute of Standards and Technology (NIST), or other internationally recognized national standards laboratories (Standard G138).  
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibili...

General Information

• Status: Published
• Publication Date: 31-May-2019
• ICS: 17.240 - Radiation measurements
• Technical Committee: G03 - Weathering and Durability
• Drafting Committee: G03.09 - Radiometry

Relations

• Replaces: ASTM G207-11 - Standard Test Method for Indoor Transfer of Calibration from Reference to Field Pyranometers
• Effective Date: 01-Jun-2019
• Refers: ASTM G138-12(2020)e1 - Standard Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
• Effective Date: 01-Jun-2020
• Refers: ASTM E824-10(2018)e1 - Standard Test Method for Transfer of Calibration From Reference to Field Radiometers
• Effective Date: 15-Apr-2018
• Refers: ASTM G113-14 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 01-Mar-2014
• Refers: ASTM E772-13 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2013
• Refers: ASTM G138-12 - Standard Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
• Effective Date: 01-Jun-2012
• Refers: ASTM E772-11 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2011
• Refers: ASTM E824-10 - Standard Test Method for Transfer of Calibration From Reference to Field Radiometers
• Effective Date: 01-Dec-2010
• Refers: ASTM G167-05(2010) - Standard Test Method for Calibration of a Pyranometer Using a Pyrheliometer
• Effective Date: 01-Dec-2010
• Refers: ASTM E816-05(2010) - Standard Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
• Effective Date: 01-Dec-2010
• Refers: ASTM G113-09 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 15-Jun-2009
• Refers: ASTM G113-08 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 01-Aug-2008
• Refers: ASTM G113-06 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 01-Dec-2006
• Refers: ASTM G113-06e1 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 01-Dec-2006
• Refers: ASTM G138-06 - Standard Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
• Effective Date: 01-Jun-2006

Overview

ASTM G207-11(2019)e1 is the internationally recognized Standard Test Method for Indoor Transfer of Calibration from Reference to Field Pyranometers. Developed by ASTM International, this document outlines procedures for calibrating pyranometers and field radiometers using artificial light sources within laboratory settings. Pyranometers are essential instruments for measuring hemispherical solar radiation, which is critical in solar energy, meteorology, weathering exposure, and climate monitoring. Indoor calibration enables reliable transfer of reference calibration under controlled conditions, ensuring measurement accuracy when field radiometers are deployed for outdoor solar irradiance and radiant exposure assessments.

Key Topics

• Calibration Methodology: Describes standardized approaches for calibrating field radiometers and pyranometers using reference instruments that have traceability to high-level standards such as the World Radiometric Reference (WRR) and National Institute of Standards and Technology (NIST).
• Artificial Light Source Configurations: Specifies the use of point and extended sources (such as banks of lamps), and enclosures with illuminated walls for radiometer exposure during calibration.
• Traceability Requirements: Emphasizes the necessity for calibration chains traceable to internationally recognized references-such as the World Radiation Center (WRC) or NIST-or participation in international pyrheliometric comparisons.
• Measurement Geometry: Ensures that both reference and field instruments maintain a consistent, horizontal orientation during calibration, corresponding with their intended deployment.
• Uncertainty and Precision: Advises on quantifying and reporting the measurement uncertainty and repeatability within laboratory calibration sessions, and details recommendations for data collection and analysis to minimize systematic errors.

Applications

The procedures set forth in ASTM G207 are indispensable in several practical applications:

• Solar Energy Measurement: Ensures the reliability of pyranometer data used for estimating energy incident on photovoltaic panels, solar collectors, and other solar harvesting devices.
• Weathering and Materials Testing: Supports accurate radiant exposure measurements for materials undergoing accelerated testing or quality assurance based on simulated sunlight exposure.
• Meteorological and Climate Studies: Facilitates the traceable calibration of sensors used in networked stations monitoring global solar irradiance, supporting climate modeling and environmental analysis.
• UV Exposure Monitoring: Applies to the calibration of instruments measuring ultraviolet radiation, essential for research in atmospheric sciences and public health.

Institutions and laboratories performing regular calibrations are encouraged to maintain multiple reference radiometers to serve as controls, ensuring long-term stability and reliability of calibration transfers.

Related Standards

ASTM G207 references and aligns with several other international and ASTM standards to ensure comprehensive coverage for pyranometer and radiometer calibration. Relevant and related standards include:

• ASTM G167 – Test Method for Calibration of a Pyranometer Using a Pyrheliometer
• ASTM E816 – Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
• ASTM E824 – Test Method for Transfer of Calibration from Reference to Field Radiometers
• ASTM G138 – Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
• ISO 9847 – Solar Energy Calibration of Field Pyranometers by Comparison to a Reference Pyranometer

These standards, along with ASTM G207, contribute to a robust framework for the accurate and traceable calibration of solar radiometers, supporting diverse fields reliant on high-quality solar irradiance data.

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Keywords: ASTM G207, pyranometer calibration, indoor calibration, radiometer traceability, field radiometers, reference pyranometer, solar irradiance measurement, artificial light source calibration, World Radiometric Reference, NIST traceability, solar energy standards.

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.
´1
Designation: G207 − 11 (Reapproved 2019)
Standard Test Method for
Indoor Transfer of Calibration from Reference to Field
Pyranometers
This standard is issued under the fixed designation G207; 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.
ε NOTE—Editorial changes were made throughout in July 2019.
INTRODUCTION
Accurate and precise measurements of total solar and solar ultraviolet irradiance are required in: (1)
the determination of the energy incident on surfaces and specimens during exposure outdoors to
various climatic factors that characterize a test site, (2) the determination of solar irradiance and
radiant exposure to ascertain the energy available to solar collection devices such as flat-plate
collectors, and (3) the assessment of the irradiance and radiant exposure in various wavelength bands
for meteorological, climatic and earth energy-budget purposes. The solar components of principal
interest include total solar radiant exposure (all wavelengths) and various ultraviolet components of
natural sunlight that may be of interest, including both total and narrow-band ultraviolet radiant
exposure.
This test method for indoor transfer of calibration from reference to field instruments is only
applicable to pyranometers and radiometers whose field angles closely approach 180° . instruments
which therefore may be said to measure hemispherical radiation, or all radiation incident on a flat
surface. Hemispherical radiation includes both the direct and sky (diffuse) geometrical components of
sunlight, while global solar irradiance refers only to hemispherical irradiance on a horizontal surface
such that the field of view includes the entire hemispherical sky dome.
For the purposes of this test method, the terms pyranometer and radiometer are used interchange-
ably.
1. Scope The essential requirement is that the reference radiometer shall
have been calibrated at horizontal tilt as employed in the
1.1 The method described in this standard applies to the
transfer of calibration.
indoor transfer of calibration from reference to field radiom-
1.5 The primary reference instrument shall not be used as a
eters to be used for measuring and monitoring outdoor radiant
field instrument and its exposure to sunlight shall be limited to
exposure levels.
outdoor calibration or intercomparisons.
1.2 This test method is applicable to field radiometers
NOTE 1—At a laboratory where calibrations are performed regularly it
regardless of the radiation receptor employed but is limited to
is advisable to maintain a group of two or three reference radiometers that
radiometers having approximately 180° (2π Steradian), field
are included in every calibration. These serve as controls to detect any
angles.
instability or irregularity in the standard reference instrument.
1.3 The calibration covered by this test method employs the
1.6 Reference standard instruments shall be stored in a
use of artificial light sources (lamps).
manner as to not degrade their calibration.
1.4 Calibrations of field radiometers are performed with
1.7 The method of calibration specified for total solar
sensors horizontal (at 0° tilt from the horizontal to the earth).
pyranometers shall be traceable to the World Radiometric
Reference (WRR) through the calibration methods of the
referencestandardinstruments(MethodG167andTestMethod
E816), and the method of calibration specified for narrow- and
This test method is under the jurisdiction of ASTM Committee G03 on
Weathering and Durability and is the direct responsibility of Subcommittee G03.09
broad-band ultraviolet radiometers shall be traceable to the
on Radiometry.
National Institute of Standards and Technology (NIST), or
CurrenteditionapprovedJune1,2019.PublishedJuly2019.Originallyapproved
other internationally recognized national standards laboratories
in 2011. Last previous edition approved in 2011 as G207 – 11. DOI: 10.1520/
G0207-11R19E01. (Standard G138).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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G207 − 11 (2019)
to fully respond to a step change in stimulus.
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.4 Energize the source to be used for the transfer of
responsibility of the user of this standard to establish appro-
calibration.
priate safety, health, and environmental practices and deter-
NOTE 3—It is mandatory that the spectral power distribution of the
mine the applicability of regulatory limitations prior to use.
source be known or well characterized. Indoor calibration transfers
1.9 This international standard was developed in accor-
between narrow band radiometers such as Ultraviolet and Photopic
dance with internationally recognized principles on standard-
detectors shall be accomplished using sources with spectral irradiance
distributions as similar as possible to the spectral distribution of the
ization established in the Decision on Principles for the
sources to be monitored.This will reduce spectral mismatch errors arising
Development of International Standards, Guides and Recom-
from differences in the spectral response of sensors and dissimilar
mendations issued by the World Trade Organization Technical
calibration and ‘test’ source spectral distributions. In the special case of
Barriers to Trade (TBT) Committee.
pyranometers for solar radiation measurements, as long as the reference
radiometer has a relatively flat and broad (greater than 700 nm passband)
2. Referenced Documents
spectral response (for example, black thermopile), or has been calibrated
2 outdoors, the difference between calibration and source spectral distribu-
2.1 ASTM Standards:
tions is less important, however should be taken into consideration.
E772 Terminology of Solar Energy Conversion
4.5 Monitor the output signal of the reference radiometer at
E816 Test Method for Calibration of Pyrheliometers by
the selected data collection interval.
Comparison to Reference Pyrheliometers
E824 Test Method for Transfer of Calibration From Refer-
4.6 Ensure the temporal stability of the source, as indicated
ence to Field Radiometers
by the reference radiometer output, has stabilized at reasonable
G113 Terminology Relating to Natural andArtificial Weath-
amplitude. Recommended source amplitude for broadband
-2 -2
ering Tests of Nonmetallic Materials
solar radiometers is in the range 500 Wm to 1000 Wm . For
G138 Test Method for Calibration of a Spectroradiometer
narrowband radiometers, a source amplitude (spectral irradi-
Using a Standard Source of Irradiance
ance distribution integrated over with respect to wavelength
G167 Test Method for Calibration of a Pyranometer Using a
over the pass band of the radiometers) of 50% to 125% of the
Pyrheliometer
peak amplitude to be expected in the source monitored by the
2.2 Other Standards: test instruments is recommended.
ISO 9847 Solar Energy Calibration of Field Pyranometers
4.7 The analog voltage signal from each radiometer is
by Comparison to a Reference Pyranometer
measured, digitized, and stored using a calibrated data-
acquisition instrument, or system. A minimum of 30 data
3. Terminology
readings is required.
3.1 Definitions:
4.8 The test data are divided by the reference radiometer
3.1.1 See Terminology E772 and G113 for terminology
data, employing the instrument constant of the reference
relating to this test method.
instrument to determine the instrument constant of the radiom-
eter being calibrated. The mean value, the standard deviation,
4. Summary of Test Method
and coefficient of variation are determined.
4.1 Mount the reference pyranometer, and the field (or test)
radiometers, or pyranometers, on a common calibration table
5. Significance and Use
for horizontal calibration. Adjust the height of the radiation
5.1 Themethodsdescribedrepresentameansforcalibration
receptor of all instruments to a common elevation.
of field radiometers employing standard reference radiometers
4.2 Connect the signal cables from the reference and test
indoors. Other methods involve the natural sunlight outdoors
sensors to a data acquisition system.
under clear skies, and various combinations of reference
4.3 Adjust the data acquisition system to record data at the
radiometers. Outdoors, these methods are useful for cosine and
selected data collection interval.
azimuth correction analyses but may suffer from a lack of
available clear skies, foreground view factor and directionality
NOTE 2—Data collection interval should be function of the time
problems. Outdoor transfer of calibrations is covered by
constant of the sensor. Sensor time constant is the period required for a
sensor to reach 1 – 1/e = 63% of the maximum minus the minimum
standards G167, E816, and E824.
amplitude of a step change in input stimulus. (e is base of natural
5.2 Several configurations of artificial sources are possible,
logarithms, 2.718282.). Often, “one over e” (1/e) time constants are
reported for radiation sensors, for example “1/e response time = 3 including:
seconds”. This represents the time for the sensor signal to reach 37% of
5.2.1 Point sources (lamps) at a distance, to which the
the full range step change representing the step change in the stimulus.
sensors are exposed.
Four times the 1/e time constant can be considered the time for the sensor
5.2.2 Extended sources (banks of lamps, or lamp(s) behind
diffusing or “homogenizing” screens) to which the sensors are
exposed.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.2.3 Various configurations of enclosures (usually spheri-
Standards volume information, refer to the standard’s Document Summary page on
cal or hemispherical) with the interior walls illuminated
the ASTM website.
indirectly with lamps. The sensors are exposed to the radiation
Available from Available from International Standards Organization (ISO), 1
Rue De Varembre, Geneva, Switzerland CH-1211 20. emanating from the enclosure walls.
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G207 − 11 (2019)
5.3 Traceability of calibration for pyranometers is accom- band of a spectroradiometer that has itself been calibrated
plished when employing the method using a reference global against such a standard source of spectral irradiance.
pyranometer that has been calibrated and is traceable to the 5.4.1.3 By comparison to a spectroradiometer that has
World Radiometric Reference (WRR). For the purposes of participated in a regional or national Intercomparison of
this test method, traceability shall have been established if a Spectroradiometers, the results of which are of reference
parent instrument in the calibration chain can be traced to a quality.
reference pyrheliometer which has participated in an Interna-
NOTE 5—The calibration of reference ultraviolet radiometers using a
tional Pyrheliometric Comparison (IPC) conducted at the
spectroradiometer, or by direct calibration against standard sources of
World Radiation Center, (WRC), Davos, Switzerland.
spectral irradiance (for example, deuterium or 1000 W tungsten-halogen
lamps) is the subject of Standard G138.
5.3.1 The reference global pyranometer (for example, one
measuring hemispherical solar radiation at all wavelengths)
5.5 The calibration method employed assumes that the
shall have been calibrated by the shading-disk, component
accuracy of the values obtained with respect to the calibration
summation, or outdoor comparison method against one of the
source used are applicable to the deployed environment, with
following instruments:
additional sources of uncertainty due to logging equipment and
5.3.1.1 Anabsolutecavitypyrheliometerthatparticipatedin
environmental effects above and beyond the calibration uncer-
a World Meteorological Organization (WMO) sanctioned
tainty.
IPC’s (and therefore possesses a WRR reduction factor).
5.6 The principal advantages of indoor calibration of radi-
5.3.1.2 An absolute cavity radiometer that has been inter-
ometers are user convenience, lack of dependence on weather,
compared (in a local or regional comparison) with an absolute
and user control of test conditions.
cavity pyrheliometer meeting 5.3.1.1.
5.7 The principal disadvantages of the indoor calibrations
5.3.1.3 Alternatively, the reference pyranometer may have
are the possible differences between natural environmental
been calibrated by direct transfer from a World Meteorological
influences and the laboratory calibration conditions with re-
Organization (WMO) First Class pyranometer that was cali-
spect to the spectral and spatial distribution of the source
brated by the shading-disk method against an absolute cavity
radiation (sun and sky versus lamps or enclosure walls).
pyrheliometer possessing a WRR reduction factor, or by direct
transfer from a WMO Standard Pyranometer (see WMO’s
5.8 It is recommended that the reference radiometer be of
Guide WMO—No. 8 for a discussion of the classification of
the same type as the test radiometer, since any difference in
solar radiometers). See Zerlaut for a discussion of the WRR,
spectral sensitivity between instruments will result in errone-
the IPC’s and their results.
ouscalibrations.However,thecalibrationofsufficientlybroad-
band detectors (approximately 700 nm or more), such as a
NOTE 4—Any of the absolute radiometers participating in the above
silicon photodiode detector with respect to extremely broad-
intercomparisons and being within 60.5 % of the mean of all similar
instruments compared in any of those intercomparisons, shall be consid-
band (more than 2000 nm) thermopile radiometers is
ered suitable as the primary reference instrument.
acceptable, as long as the additional increased uncertainty in
5.4 Traceability of calibration of narrow band (for example, the field measurements, due to spectral response and spectral
Ultraviolet) radiometers is accomplished when employing the
mismatch limitations, is acceptable. The reader is referred to
7 8
methodusingareferencenarrowbandradiometerthathasbeen ISO TR 9673 and ISO TR 9901 for discussions of the types
calibratedandistraceabletotheNationalInstituteofStandards
of instruments available and their use.
and Technology (NIST), or other national standards organiza-
tions. 6. Interferences
5.4.1 The reference narrow band radiometer, regardless of
6.1 In order to minimize systematic errors the reference and
whether it measures total ultraviolet solar radiation, or narrow-
test radiometers must be as nearly alike in all respects as
band UV-A or UV-B radiation, or a defined narrow band
possible.
segment of ultraviolet radiation, shall have been calibrated by
6.1.1 The spectral response of both the reference and test
one of the following:
radiometers should be as nearly identical as possible.
5.4.1.1 By comparison to a standard source of spectral
6.1.2 The spectral content (spectral power distribution) of
irradiance that is traceable to NIST or to the appropriate
the calibration source and the source to be monitored in the
national standards organizations of other countries using ap-
field experiment should be matched to greatest extent possible.
propriate filters and filter correction factors [for example,
If not, the relative spectral differences should be characterized,
Drummond ].
reported, and the spectral mismatch characterized.
5.4.1.2 By comparison of the radiometer output to the
6.2 Source stability. The measurements selected in deter-
integrated spectral irradiance in the appropriate wavelength
mining the instrument constant shall be made during periods of
essentially uniform levels or slow (less than 0.5% of full scale
WMO—No. 8, “Guide to Meteorological Instruments and Methods of
Observation,” Fifth Ed., World Meteorological Organization, Geneva, Switzerland,
1983.
Zerlaut, G. A., “Solar Radiation Instrumentation,” Chapter 5 in Solar ISO Technical Report TR 9673, “Solar Radiation and Its Measurement for
Resources, The MIT Press, Cambridge, MA, 1989, pp. 173–308. Determining Outdoor Weathering Exposure Levels,” International Standards
Drummond, A.J, and A.K. Ǻngström, “Derivation of the Photometric Flux of Organization, Geneva, Switzerland.
Daylight from Filtered Measurements of Global (Sun and Sky) Radiant Energy”, ISO/TR 9901:1990, “Solar Energy—Field Pyranometers—Recommended
Applied Optics Vol 10 # 9, September 1971. Practice for Use.”
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G207 − 11 (2019)
per minute) rates of change of radiation (as measured by the 7.3.2.1 Spatial uniformity in the “test plane” of the sensors
reference radiometer). Measurements selected under varying may be evaluated by recording the maximum difference
source amplitudes may result in erroneous calibrations if the between an initial (first placement) reference radiometer signal
reference and test radiometers possess significantly different and subsequent placements of the reference radiometer in each
response times. test instrument position (until a sample size of at least 20 is
reached). The maximum difference between the signal at the
6.3 Spatial non-uniformity in the test plane with respect to
starting placement and any other placement should not exceed
the location of reference and test detectors will lead to
1% of the expected (full scale) amplitude.
erroneous results, on the order of magnitude of the non-
7.3.2.2 If the test instrument and the reference instrument
uniformity.
are replaced in the same location, record the maximum
difference between an initial (first placement) of the reference
7. Apparatus
radiometer signal and subsequent removal and re-placements
7.1 Data Acquisition Instrument—A digital voltmeter or
of the reference radiometer in the calibration position. A
data logger capable of repeatability to 0.1 % of average
sample size of at least 20 (removal and replacements) of the
reading,andanuncertaintyof 60.2%withinputimpedanceof
reference radiometer are needed. The maximum difference
at least 1 MΩ may be employed. Data loggers having printout
between the signal at the starting placement and any other
mustbecapableofameasurementfrequencyofatleasttwoper
placement should not exceed 1% of the expected (full scale)
minute. A data logger having three-channel capacity may be
amplitude.
useful.
7.3.3 The spectral distribution of incandescent, xenon arc,
metal halide, light emitting diodes, and other lamp technolo-
7.2 Fixed-Angle
...