ASTM E1341-96(2001)
(Practice)Standard Practice for Obtaining Spectroradiometric Data from Radiant Sources for Colorimetry
Standard Practice for Obtaining Spectroradiometric Data from Radiant Sources for Colorimetry
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, or 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E1341–96 (Reapproved 2001)
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 (e) 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
modifications to the procedures given in Practice E308 that are necessary for computing the absolute
luminance of radiant sources.
1. Scope of Ultraviolet, Visible, and Near-Infrared Spectrophotom-
eters
1.1 This practice prescribes the instrumental measurement
E284 Terminology of Appearance
requirements, calibration procedures, and physical standards
E308 Practice for Computing the Colors of Objects by
needed for precise spectroradiometric data for characterizing
Using the CIE System
the color and luminance of radiant sources.
E387 Test Method for Estimating Stray Radiant Power
1.2 This practice lists the parameters that must be specified
RatioofSpectrophotometersbytheOpaqueFilterMethod
whenspectroradiometricmeasurementsarerequiredinspecific
E925 PracticeforthePeriodicCalibrationofNarrowBand-
methods, practices, or specifications.
Pass Spectrophotometers
1.3 This practice describes the unique calculation proce-
E958 Practice for Measuring Practical Spectral Bandwidth
duresrequiredtodeterminebasiccolorimetricdataofluminous
of Ultraviolet-Visible Spectrophotometers
sources.
2.2 NIST Publications:
1.4 This practice is general in scope rather than specific as
NIST Technical Note 594-1 Fundamental Principles ofAb-
to instrument, object, or material.
solute Radiometry and the Philosophy of the NBS Pro-
1.5 The values stated in SI units are to be regarded as the
gram (1968–1971)
standard.
NISTTechnical Note 594-3 Photometric Calibration Proce-
1.6 This standard does not purport to address all of the
dures
safety concerns, if any, associated with its use. It is the
2.3 CIE Publications:
responsibility of the user of this standard to establish appro-
Publication CIE No. 15.2 Colorimetry, 2nd ed., 1986
priate safety and health practices and determine the applica-
Publication CIE No. 38 Radiometric and Photometric
bility of regulatory limitations prior to use.
CharacteristicsofMaterialsandtheirMeasurement,1977
2. Referenced Documents PublicationCIENo.63 SpectroradiometricMeasurementof
Light Sources, 1984
2.1 ASTM Standards:
E275 Practice for Describing and Measuring Performance
Annual Book of ASTM Standards, Vol 03.06.
Annual Book of ASTM Standards, Vol 06.01.
1 4
This test method is under the jurisdiction of ASTM Committee E12 on Color Available from National Institute of Standards and Technology (NIST),
and Appearance and is the direct responsibility of Subcommittee E12.06 on Gaithersburg, MD 20899–0001.
Appearance of Displays. Currently available through the U.S. National Committee of the CIE, c/o Mr.
Current edition approved June 10, 1996. Published August 1996. Originally Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 Pond Street, Salem, MA
published as E1341–91. Last previous edition E1341–91. 01970-4819.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1341
2.4 IES Standard: to the spectroradiometer, and the presence of any special
IES Guide to Spectroradiometric Measurements, 1983 intermediate optical devices such as integrating spheres.
2.5 ANSI Standard:
6.1.3 Thespectralparameters,includingthespectralregion,
ANSI/IES RP-16-1980 Nomenclature and Definitions for wavelength measurement interval, and spectral bandwidth.
Illuminating Engineering
6.1.4 The type of standard used to calibrate the system, a
standardlamp,acalibratedsource,oracalibrateddetector,and
3. Terminology
the source of the calibration.
3.1 Definitions:
3.1.1 The definitions of appearance terms in Terminology
7. Apparatus
E284 are applicable to this practice.
7.1 The basic instrument requirement is a spectroradiomet-
ric system designed for the measurement of spectral radiance
4. Summary of Practice
or irradiance of light sources. The basic elements of a spectro-
4.1 Procedures are given for selecting the types and oper-
radiometric system are calibration sources with their regulated
ating parameters of spectroradiometers used to produce data
power supplies, a light detector, electronics for measuring the
for the calculation of CIE tristimulus values and other color
photocurrents, a monochromator with control equipment for
coordinates to describe the colors of radiant sources. The
computer interfacing, receiving optics, and a computer as
important steps of the calibration of such instruments, and the
described in CIE 63 and IES Guide to Spectroradiometric
standards required for these steps, are described. Parameters
Measurements.Thecomputerislistedasanintegralpartofthe
are identified that must be specified when spectroradiometric
system since the required precision is unobtainable without
measurements are required in specific methods or other docu-
automated control. The characteristics of each element are
ments. Modifications to Practice E308 are described in order
discussed in the following sections.
to account for the differences between objects and radiant
7.2 Calibration Sources—The standard calibration lamp for
sources.
spectroradiometry is a tungsten-filament lamp operated at a
specified current. Such lamps are available from many stan-
5. Significance and Use
dardizinglaboratories.Typicalofsuchstandardsisthetungsten
5.1 The fundamental method for obtaining CIE tristimulus
filament, 1000 W, halogen cycle, quartz-envelope FEL-type
values or other color coordinates for describing the colors of
lamp recommended by the National Institute of Standards and
radiant sources is by the use of spectroradiometric measure-
Technology (NIST). (See NIST Tech Note 594-1, and 594-3.)
ments. These measurements are used by summation together
Uncertainties in the transfer of the scale of spectral radiance or
with numerical values representing the CIE 1931 Standard
irradianceareabout1%.Itispreferabletohavemorethanone
Observer(CIEpublicationNo.15.2)andnormalizedto K ,the
m
standardsourcetopermitcross-checksandtoallowcalibration
maximum spectral luminous efficacy function, with a value of
at a range of illuminance levels. Such sources can be con-
683 lm/W.
structed from lamps operating at any color temperature and
5.2 This practice provides a procedure for selecting the
spectral nature that have been characterized against a standard
operating parameters of spectroradiometers used for providing
lamp. Monochromatic emission sources, such as a low-
the desired precision spectroradiometric data, for their calibra-
pressure mercury arc lamp or tunable laser, should also be
tion, and for the physical standards required for calibration.
available for use in calibrating the wavelength scale in accor-
5.3 Special requirements for characterizing sources of light
dancewithPracticeE925.Multilinelasers,suchascontinuous
possessing narrow or discontinuous spectra are presented and
wave(cw)argon-ionandhelium-neon,arepreferredsincethey
discussed. Modifications to the procedures of Practice E308
can be tuned to a small number of lines of well known
are given to correct for the unusual nature of narrow or
wavelengths.
discontinuous sources.
7.2.1 Calibration Source Power Supplies— The electrical
supplies for the calibration sources should be of the constant
6. Requirements When Using Spectroradiometry
current type. The supply should be linear and not a switching
6.1 Whendescribingthemeasurementofradiantsourcesby
supply. Current regulation should be maintained to better than
spectroradiometry, the following must be specified.
0.1%. This level of regulation is required to maintain a
6.1.1 The radiometric quantity determined, such as the
2 2 constant flux across the entrance to the spectroradiometer.
irradiance (W/m ) or radiance (W/m -sr), or the photometric
2 7.2.2 A standard for the measurement of length (such as a
quantitydetermined,suchasilluminance(lm/m )orluminance
2 2 high-quality metric rule) should also be available since abso-
(lm/m -sr or cd/m ). The use of older, less descriptive names
lute irradiance calibrations must be performed at exact dis-
or units such as phot, nit, stilb (see ANSI/IES RP-16-1980) is
tances from the filament of the standard lamp.
not recommended.
7.3 Detectors:
6.1.2 The geometry of the measurement conditions, includ-
7.3.1 Photomultiplier Tubes—Photomultiplier tubes are the
ing whether a diffuser was used and its material of construc-
traditional detectors in spectroradiometers. This is due to their
tion,thedistancesfromthesourceofirradiationtotheentrance
superior performance in low-light-level conditions such as are
encountered at the exit slit of a low-efficiency monochromator.
The photocathodes of photomultipliers are sensitive to tem-
Available from American National Standards Institute, 1430 Broadway, NY,
NY 10018–3308. perature, polarization, and magnetic fields. Light levels on the
E1341
photocathode should never be allowed to generate photocur- intermediate focusing lens or mirror assembly. Care should be
−6
rents in excess of 10 A. The high-voltage supply should be taken to use a magnification that will adequately fill the
stabilized to better than 0.01% since the gain of the multiplier entranceslitwhenviewingboththecalibrationandtestsource.
tube is controlled by the voltage across the dynodes. The CIE recommends the use of a rotatable integrating sphere
as the input optics (CIE No. 63). The entrance port of the
7.3.2 Silicon Photodiodes—Recently, silicon photodiodes
sphereisrotatedtoviewfirstthecalibrationsourceandthento
have superseded photomultiplier tubes in radiometric instru-
viewthetestsource.Sincetheefficiencyofintegratingspheres
ments. Photodiodes are less sensitive to temperature, polariza-
tend to be rather low, this method is only useful for bright
tion,andmagneticfieldsthanphotomultipliers,butcareshould
sources.
still be taken to control these variables.
7.6 Computer System:
7.4 Monochromators—The monochromator is the wave-
7.6.1 There are no special requirements for the computer.
length dispersive element in the system. The region of the
Any minicomputer or microcomputer should suffice. The
monochromator should be 360 nm to 830 nm for highest
program should control or monitor as many of the instrument
accuracy, but a region of 380 nm to 780 nm should suffice for
parameters as possible. Included in the computer system is the
most characterizations.The bandwidth should be kept constant
analog to digital conversion process, which changes the pho-
across the region of measurement at between 85% and 100%
tocurrents to voltages, amplifies the voltages, and digitizes the
of the measurement interval, but no greater than 5.0 nm. The
voltages into computer-readable signals.A3 ⁄2 digit autorang-
CIE recommends a 1.0 nm bandwidth and measurement
ing digital ammeter with a computer interface is suitable for
interval for highest accuracy, and suggests 2.0 nm as a
this purpose.Alternatively, an autoranging electrometer with a
compromise for characterizing radiation sources with spectra
computer interface can be used, but shielding and guarding of
that contain both continuous and line emissions (CIE No. 63).
the low level signals becomes more critical. This is equivalent
The precision of the wavelength setting should be 0.1 nm with
to a twelve bitADC (analog to digital converter) with variable
an absolute accuracy of better than 0.5 nm.The size and shape
gains on the input signal. The use of a detector housing with a
of the entrance and exit slits of the monochromator should be
built-in current to voltage amplifier is recommended since the
chosen to provide a symmetric bandshape, preferably triangu-
photocurrents are very small and can be affected by stray
lar.Theentranceslitshouldbecompletelyanduniformlyfilled
electromagnetic fields and capacitances. Amplification and
with light. Specialized versions of the general spectroradiom-
conversion to voltage at the detector package minimizes these
eter may be constructed and used for specific applications
effects and will provide the voltage signal necessary for
wheretheinstrumentcandepartfromtheaboveguidelines.For
common ADC converters that are available for mini and
example, a source with little or no radiant energy in the far red
microcomputers.
end of the visible spectrum may be correctly characterized by
7.6.2 The data that is acquired by the computer should be
measurements to 700 or 710 nm rather than 780 nm.
converted and displayed as real number values. The raw
7.4.1 Scanning Monochromators—The newer technology
readings should be corrected for dark current by subtraction of
of holographically reproduced gratings has made possible the
the measured signal with no light impinging on the entrance to
productionofsingle-anddouble-gratingmonochromatorswith
the monochromator, and then scaled to the absolute values of
very high throughputs and very low stray-light levels. Second-
the calibration source measurements. The results can be
order spectra need to be eliminated through the use of either a
displayed on any appropriate device, though a printed copy is
predisperser or a long-pass filter. A drive mechanism and
adesirableoption.Thecorrectedvaluesshouldbestoredonthe
positionencodershouldbeattachedtothescanningmonochro-
computer’s storage media for later processing. The generation
mator drive to allow the monochromator to scan the wave-
ofaplotofnormalizedradiance(irradiance)versuswavelength
length region under control of a computer. Prism-based scan-
is also desirable, since a skilled operator will be able to obtain
ning monochromators can also be used though the drive
much useful information for both diagnostic and analytic
mechanism is more complex and the slit width must be
purposes from the graph.
changed as a function of the wavelength to maintain constant
bandwidth.
8. Calibration an
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.