ASTM E1341-16(2020)

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: E1341 − 16 (Reapproved 2020)
Standard Practice for
Obtaining Spectroradiometric Data from Radiant Sources
for Colorimetry
This standard is issued under the fixed designation E1341; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The fundamental procedure for characterizing the color and absolute luminance of radiant sources
is to obtain the spectroradiometric data under specified measurement conditions, and from these data
to compute CIE chromaticity coordinates and luminance values based on the CIE 1931 Standard
Observer. The considerations involved and the procedures to be used to obtain precision spectrora-
diometricdataforthispurposearecontainedinthispractice.Thevaluesandproceduresforcomputing
CIE chromaticity coordinates are contained in Practice E308. This practice includes minor modifi-
cations to the procedures given in Practice E308 that are necessary for computing the absolute
luminance of radiant sources.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This practice prescribes the instrumental measurement
mendations issued by the World Trade Organization Technical
requirements, calibration procedures, and physical standards
Barriers to Trade (TBT) Committee.
needed for precise spectroradiometric data for characterizing
the color and luminance of radiant sources.
2. Referenced Documents
1.2 This practice lists the parameters that must be specified
2.1 ASTM Standards:
whenspectroradiometricmeasurementsarerequiredinspecific
E275PracticeforDescribingandMeasuringPerformanceof
methods, practices, or specifications.
Ultraviolet and Visible Spectrophotometers
1.3 This practice describes the unique calculation proce-
E284Terminology of Appearance
duresrequiredtodeterminebasiccolorimetricdataofluminous
E308PracticeforComputingtheColorsofObjectsbyUsing
sources.
the CIE System
1.4 This practice is general in scope rather than specific as E387TestMethodforEstimatingStrayRadiantPowerRatio
to instrument, object, or material. of Dispersive Spectrophotometers by the Opaque Filter
Method
1.5 The values stated in SI units are to be regarded as
E925Practice for Monitoring the Calibration of Ultraviolet-
standard. No other units of measurement are included in this
Visible Spectrophotometers whose Spectral Bandwidth
standard.
does not Exceed 2 nm
1.6 This standard does not purport to address all of the
E958Practice for Estimation of the Spectral Bandwidth of
safety concerns, if any, associated with its use. It is the
Ultraviolet-Visible Spectrophotometers
responsibility of the user of this standard to establish appro-
2.2 NIST Publications:
priate safety, health, and environmental practices and deter-
NIST Technical Note 594-1Fundamental Principles of Ab-
mine the applicability of regulatory limitations prior to use.
solute Radiometry and the Philosophy of the NBS Pro-
1.7 This international standard was developed in accor-
gram (1968–1971)
dance with internationally recognized principles on standard-
1 2
This practice is under the jurisdiction ofASTM Committee E12 on Color and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Appearance and is the direct responsibility of Subcommittee E12.06 on Display, contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Imaging and Imaging Colorimetry. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2020. Published October 2020. Originally the ASTM website.
approved in 1991. Last previous edition approved in 2016 as E1341–16. DOI: Available from National Institute of Standards and Technology (NIST), 100
10.1520/E1341-16R20. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1341 − 16 (2020)
NIST Technical Note 594-3Photometric Calibration Proce- 6. Requirements When Using Spectroradiometry
dures
6.1 Whendescribingthemeasurementofradiantsourcesby
2.3 CIE Publications:
spectroradiometry, the following must be specified.
CIE Publication 015:2004Colorimetry, 3rd ed.
6.1.1 The radiometric quantity determined, such as the
2 2
CIE Publication No. 38 Radiometric and Photometric Char-
irradiance (W/m ) or radiance (W/m -sr), or the photometric
acteristics of Materials and their Measurement, 1977
quantitydetermined,suchasilluminance(lm/m )orluminance
2 2
CIE Publication No. 63Spectroradiometric Measurement of
(lm/m -srorcd/m ).Theuseofolder,lessdescriptivenamesor
Light Sources, 1984
units such as phot, nit, stilb (seeANSI/IES RP-16-1980) is not
2.4 IES Standard: recommended.
IES Guide to Spectroradiometric Measurements, 1983
6.1.2 The geometry of the measurement conditions, includ-
ing whether a diffuser was used and its material of
2.5 ANSI Standard:
construction, the distances from the source of irradiation to the
ANSI/IES RP-16-1980Nomenclature and Definitions for
entrance to the spectroradiometer, and the presence of any
Illuminating Engineering
special intermediate optical devices such as integrating
3. Terminology spheres.
6.1.3 Thespectralparameters,includingthespectralregion,
3.1 Definitions:
wavelength measurement interval, and spectral bandwidth.
3.1.1 The definitions of appearance terms in Terminology
6.1.4 The type of standard used to calibrate the system, a
E284 are applicable to this practice.
standardlamp,acalibratedsource,oracalibrateddetector,and
the source of the calibration.
4. Summary of Practice
4.1 Procedures are given for selecting the types and oper-
7. Apparatus
ating parameters of spectroradiometers used to produce data
7.1 The basic instrument requirement is a spectroradiomet-
for the calculation of CIE tristimulus values and other color
ric system designed for the measurement of spectral radiance
coordinates to describe the colors of radiant sources. The
or irradiance of light sources. The basic elements of a spectro-
important steps of the calibration of such instruments, and the
radiometric system are calibration sources with their regulated
standards required for these steps, are described. Parameters
power supplies, a light detector, electronics for measuring the
are identified that must be specified when spectroradiometric
photocurrents, a monochromator with control equipment for
measurements are required in specific methods or other docu-
computer interfacing, receiving optics, and a computer as
ments.ModificationstoPracticeE308aredescribedinorderto
described in CIE Publication No. 63 and IES Guide to
account for the differences between objects and radiant
Spectroradiometric Measurements. The computer is listed as
sources.
an integral part of the system since the required precision is
unobtainable without automated control.The characteristics of
5. Significance and Use
each element are discussed in the following sections.
5.1 The fundamental method for obtaining CIE tristimulus
7.2 Calibration Sources—The standard calibration lamp for
values or other color coordinates for describing the colors of
spectroradiometry is a tungsten-filament lamp operated at a
radiant sources is by the use of spectroradiometric measure-
specified current. Such lamps are available from many stan-
ments. These measurements are used by summation together
dardizinglaboratories.Typicalofsuchstandardsisthetungsten
with numerical values representing the CIE 1931 Standard
filament, 1000 W, halogen cycle, quartz-envelope FEL-type
Observer (CIE Publication 015:2004) and normalized to K ,
m
lamp recommended by the National Institute of Standards and
themaximumspectralluminousefficacyfunction,withavalue
Technology (NIST). (See NIST Technical Note 594-1, and
of 683 lm/W.
594-3.) Uncertainties in the transfer of the scale of spectral
5.2 This practice provides a procedure for selecting the
radiance or irradiance are about 1%. It is preferable to have
operating parameters of spectroradiometers used for providing
more than one standard source to permit cross-checks and to
the desired precision spectroradiometric data, for their
allowcalibrationatarangeofilluminancelevels.Suchsources
calibration, and for the physical standards required for calibra-
can be constructed from lamps operating at any color tempera-
tion.
ture and spectral nature that have been characterized against a
5.3 Special requirements for characterizing sources of light standard lamp. Monochromatic emission sources, such as a
possessing narrow or discontinuous spectra are presented and low-pressure mercury arc lamp or tunable laser, should also be
discussed.ModificationstotheproceduresofPracticeE308are available for use in calibrating the wavelength scale in accor-
given to correct for the unusual nature of narrow or discon- dance with Practice E925. Multiline lasers, such as continuous
tinuous sources. wave(cw)argon-ionandhelium-neon,arepreferredsincethey
can be tuned to a small number of lines of well known
wavelengths.
AvailablefromU.S.NationalCommitteeoftheCIE(InternationalCommission
7.2.1 Calibration Source Power Supplies—The electrical
on Illumination), C/o Alan Laird Lewis, 282 E. Riding, Carlisle, MA 01741,
supplies for the calibration sources should be of the constant
http://www.cie-usnc.org.
current type. The supply should be linear and not a switching
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. supply. Current regulation should be maintained to better than
E1341 − 16 (2020)
0.1%. This level of regulation is required to maintain a mechanism is more complex and the slit width must be
constant flux across the entrance to the spectroradiometer. changed as a function of the wavelength to maintain constant
bandwidth.
7.2.2 A standard for the measurement of length (such as a
7.4.2 Polychromators—Photodiode arrays are used in flat-
high-quality metric rule) should also be available since abso-
field spectrographic radiometers. The bandwidth and sampling
lute irradiance calibrations must be performed at exact dis-
interval are determined by the pitch of the array and the
tances from the filament of the standard lamp.
reciprocallineardispersionofthespectrograph.Theguidelines
7.3 Detectors:
given above should be followed for the diode array instrument
7.3.1 Photomultiplier Tubes—Photomultiplier tubes are the
as well.
traditional detectors in spectroradiometers. This is due to their
7.5 Receiving Optics—To maximize the light throughput,
superior performance in low-light-level conditions such as are
the number of optical surfaces between the source of light
encountered at the exit slit of a low-efficiency monochromator.
(either a calibration or test source) and the monochromator
The photocathodes of photomultipliers are sensitive to
entrance slit should be kept to a minimum. In extended diffuse
temperature, polarization, and magnetic fields. Light levels on
sources, only a set of limiting apertures may be needed. For
the photocathode should never be allowed to generate photo-
small sources a diffusing element may be required, such as a
−6
currents in excess of 10 A. The high-voltage supply should
PTFE-fluorocarbon cap or integrating sphere. In some
be stabilized to better than 0.01% since the gain of the
instances, it may be desirable to image the source with an
multiplier tube is controlled by the voltage across the dynodes.
intermediate focusing lens or mirror assembly. Care should be
7.3.2 Silicon Photodiodes—Recently, silicon photodiodes
taken to use a magnification that will adequately fill the
have superseded photomultiplier tubes in radiometric instru-
entranceslitwhenviewingboththecalibrationandtestsource.
ments. Photodiodes are less sensitive to temperature,
The CIE recommends the use of a rotatable integrating sphere
polarization, and magnetic fields than photomultipliers, but
as the input optics (CIE Publication No. 63).The entrance port
careshouldstillbetakentocontrolthesevariables.Twosilicon
of the sphere is rotated to view first the calibration source and
photodiode based detectors used in instrumentation are Charge
then to view the test source. Since the efficiency of integrating
Coupled Devises (CCD) and Complimentary Metal Oxide
spheres tend to be rather low, this method is only useful for
Silicon (CMOS).
bright sources.
7.4 Monochromators—The monochromator is the wave-
7.6 Computer System:
length dispersive element in the system. The region of the
7.6.1 There are no special requirements for the computer.
monochromator should be 360 to 830 nm for highest accuracy,
Any minicomputer or microcomputer should suffice. The
but a region of 380 to 780 nm should suffice for most
program should control or monitor as many of the instrument
characterizations. The bandwidth should be kept constant
parameters as possible. Included in the computer system is the
across the region of measurement at between 85 and 100% of
analog to digital conversion process, which changes the pho-
the measurement interval, but no greater than 5.0 nm.The CIE
tocurrents to voltages, amplifies the voltages, and digitizes the
recommendsa1.0nmbandwidthandmeasurementintervalfor
voltages into computer-readable signals.A3 ⁄2 digit autorang-
highest accuracy, and suggests 2.0 nm as a compromise for
ing digital ammeter with a computer interface is suitable for
characterizing radiation sources with spectra that contain both
this purpose.Alternatively, an autoranging electrometer with a
continuous and line emissions (CIE Publication No. 63). The
computer interface can be used, but shielding and guarding of
precision of the wavelength setting should be 0.1 nm with an
the low level signals becomes more critical. This is equivalent
absolute accuracy of better than 0.5 nm. The size and shape of
to a twelve bitADC (analog to digital converter) with variable
the entrance and exit slits of the monochromator should be
gains on the input signal. The use of a detector housing with a
chosen to provide a symmetric bandshape, preferably triangu-
built-in current to voltage amplifier is recommended since the
lar.Theentranceslitshouldbecompletelyanduniformlyfilled
photocurrents are very small and can be affected by stray
with light. Specialized versions of the general spectroradiom-
electromagnetic fields and capacitances. Amplification and
eter may be constructed and used for specific applications
conversion to voltage at the detector package minimizes these
wheretheinstrumentcandepartfromtheaboveguidelines.For
effects and will provide th
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