ASTM E1341-06(2011)e1
(Practice)Standard Practice for Obtaining Spectroradiometric Data from Radiant Sources for Colorimetry
Standard Practice for Obtaining Spectroradiometric Data from Radiant Sources for Colorimetry
SIGNIFICANCE AND USE
The fundamental method for obtaining CIE tristimulus values or other color coordinates for describing the colors of radiant sources is by the use of spectroradiometric measurements. These measurements are used by summation together with numerical values representing the CIE 1931 Standard Observer (CIE Publication 015:2004) and normalized to Km, the maximum spectral luminous efficacy function, with a value of 683 lm/W.
This practice provides a procedure for selecting the operating parameters of spectroradiometers used for providing the desired precision spectroradiometric data, for their calibration, and for the physical standards required for calibration.
Special requirements for characterizing sources of light possessing narrow or discontinuous spectra are presented and discussed. Modifications to the procedures of Practice E308 are given to correct for the unusual nature of narrow or discontinuous sources.
SCOPE
1.1 This practice prescribes the instrumental measurement requirements, calibration procedures, and physical standards needed for precise spectroradiometric data for characterizing the color and luminance of radiant sources.
1.2 This practice lists the parameters that must be specified when spectroradiometric measurements are required in specific methods, practices, or specifications.
1.3 This practice describes the unique calculation procedures required to determine basic colorimetric data of luminous sources.
1.4 This practice is general in scope rather than specific as to instrument, object, or material.
1.5 The values stated in SI units are to be regarded as the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E1341 − 06 (Reapproved 2011)
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.
ε NOTE—Reference to CIE Publication 015:2004 was corrected editorially throughout in November 2011.
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 2. Referenced Documents
1.1 This practice prescribes the instrumental measurement 2.1 ASTM Standards:
requirements, calibration procedures, and physical standards E275PracticeforDescribingandMeasuringPerformanceof
needed for precise spectroradiometric data for characterizing Ultraviolet and Visible Spectrophotometers
the color and luminance of radiant sources. E284Terminology of Appearance
E308PracticeforComputingtheColorsofObjectsbyUsing
1.2 This practice lists the parameters that must be specified
the CIE System
whenspectroradiometricmeasurementsarerequiredinspecific
E387TestMethodforEstimatingStrayRadiantPowerRatio
methods, practices, or specifications.
of Dispersive Spectrophotometers by the Opaque Filter
1.3 This practice describes the unique calculation proce-
Method
duresrequiredtodeterminebasiccolorimetricdataofluminous
E925Practice for Monitoring the Calibration of Ultraviolet-
sources.
Visible Spectrophotometers whose Spectral Bandwidth
does not Exceed 2 nm
1.4 This practice is general in scope rather than specific as
to instrument, object, or material. E958Practice for Estimation of the Spectral Bandwidth of
Ultraviolet-Visible Spectrophotometers
1.5 The values stated in SI units are to be regarded as the
2.2 NIST Publications:
standard.
NIST Technical Note 594-1Fundamental Principles of Ab-
1.6 This standard does not purport to address all of the
solute Radiometry and the Philosophy of the NBS Pro-
safety concerns, if any, associated with its use. It is the
gram (1968–1971)
responsibility of the user of this standard to establish appro-
NIST Technical Note 594-3Photometric Calibration Proce-
priate safety and health practices and determine the applica-
dures
bility of regulatory limitations prior to use.
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 Nov. 1, 2011. Published November 2011. Originally the ASTM website.
Available from National Institute of Standards and Technology (NIST), 100
approved in 1991. Last previous edition approved in 2006 as E1341–06. DOI:
Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
10.1520/E1341-06R11E01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E1341 − 06 (2011)
2.3 CIE Publications: 6.1.1 The radiometric quantity determined, such as the
4 2 2
CIE Publication 015:2004Colorimetry, 3rd ed. irradiance (W/m ) or radiance (W/m -sr), or the photometric
CIE Publication No. 38 Radiometric and Photometric Char- quantity determined, such as illuminance (lm/m ) or lumi-
4 2 2
acteristics of Materials and their Measurement, 1977 nance (lm/m -sr or cd/m ). The use of older, less descriptive
CIE Publication No. 63Spectroradiometric Measurement of
names or units such as phot, nit, stilb (see ANSI/IES RP-16-
Light Sources, 1984 1980) is not recommended.
2.4 IES Standard:
6.1.2 The geometry of the measurement conditions, includ-
IES Guide to Spectroradiometric Measurements, 1983
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
spheres.
3. Terminology
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
4. Summary of Practice the source of the calibration.
4.1 Procedures are given for selecting the types and oper-
7. Apparatus
ating parameters of spectroradiometers used to produce data
for the calculation of CIE tristimulus values and other color
7.1 The basic instrument requirement is a spectroradiomet-
coordinates to describe the colors of radiant sources. The
ric system designed for the measurement of spectral radiance
important steps of the calibration of such instruments, and the
or irradiance of light sources. The basic elements of a spectro-
standards required for these steps, are described. Parameters
radiometric system are calibration sources with their regulated
are identified that must be specified when spectroradiometric
power supplies, a light detector, electronics for measuring the
measurements are required in specific methods or other docu-
photocurrents, a monochromator with control equipment for
ments.ModificationstoPracticeE308aredescribedinorderto
computer interfacing, receiving optics, and a computer as
account for the differences between objects and radiant
described in CIE Publication No. 63 and IES Guide to
sources.
Spectroradiometric Measurements. The computer is listed as
an integral part of the system since the required precision is
5. Significance and Use
unobtainable without automated control.The characteristics of
5.1 The fundamental method for obtaining CIE tristimulus
each element are discussed in the following sections.
values or other color coordinates for describing the colors of
7.2 Calibration Sources—The standard calibration lamp for
radiant sources is by the use of spectroradiometric measure-
spectroradiometry is a tungsten-filament lamp operated at a
ments. These measurements are used by summation together
specified current. Such lamps are available from many stan-
with numerical values representing the CIE 1931 Standard
dardizinglaboratories.Typicalofsuchstandardsisthetungsten
Observer (CIE Publication 015:2004) and normalized to K ,
m
filament, 1000 W, halogen cycle, quartz-envelope FEL-type
themaximumspectralluminousefficacyfunction,withavalue
lamp recommended by the National Institute of Standards and
of 683 lm/W.
Technology (NIST). (See NIST Technical Note 594-1, and
5.2 This practice provides a procedure for selecting the
594-3.) Uncertainties in the transfer of the scale of spectral
operating parameters of spectroradiometers used for providing
radiance or irradiance are about 1%. It is preferable to have
the desired precision spectroradiometric data, for their
more than one standard source to permit cross-checks and to
calibration, and for the physical standards required for calibra-
allowcalibrationatarangeofilluminancelevels.Suchsources
tion.
can be constructed from lamps operating at any color tempera-
5.3 Special requirements for characterizing sources of light
ture and spectral nature that have been characterized against a
possessing narrow or discontinuous spectra are presented and
standard lamp. Monochromatic emission sources, such as a
discussed.ModificationstotheproceduresofPracticeE308are
low-pressure mercury arc lamp or tunable laser, should also be
given to correct for the unusual nature of narrow or discon-
available for use in calibrating the wavelength scale in accor-
tinuous sources.
dance with Practice E925. Multiline lasers, such as continuous
wave(cw)argon-ionandhelium-neon,arepreferredsincethey
6. Requirements When Using Spectroradiometry
can be tuned to a small number of lines of well known
6.1 Whendescribingthemeasurementofradiantsourcesby
wavelengths.
spectroradiometry, the following must be specified.
7.2.1 Calibration Source Power Supplies—The electrical
supplies for the calibration sources should be of the constant
AvailablefromU.S.NationalCommitteeoftheCIE(InternationalCommission
current type. The supply should be linear and not a switching
on Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond
supply. Current regulation should be maintained to better than
St., Salem, MA 01970, http://www.cie-usnc.org.
0.1%. This level of regulation is required to maintain a
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. constant flux across the entrance to the spectroradiometer.
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E1341 − 06 (2011)
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
given above should be followed for the diode array instrument
7.3 Detectors:
as well.
7.3.1 Photomultiplier Tubes—Photomultiplier tubes are the
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
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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 the voltage signal necessary for
example, a source with little or no radiant energy in the far red
common ADC converters that are available for mini and
end of the visible spectrum may be correctly characterized by
microcomputers.
measurements to 700 or 710
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