ASTM G138-96
(Test Method)Standard Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
Standard Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
SCOPE
1.1 This test method covers the calibration of spectroradiometers for the measurement of spectral irradiance using a standard of special irradiance that is traceable to NIST.
Note- Although NIST is referenced throughout this standard, it should be assumed that other internationally recognized standards laboratories may be substituted.
1.2 This method is not limited by the input optics of the spectroradiometric system. However, choice of input optics affects the overall uncertainty of the calibration.
1.3 This method is not limited by the type of monochromator or optical detector used in the spectroradiometer system. Parts of the method may not apply to determine which parts apply to the specific spectroradiometer being used. It is important that the choice of monochromator and detector be appropriate for the wavelength range of interest for the calibration. Though the method generally applies to photodiode array detector based systems, the user should note that these types of spectroradiometers often suffer from stray light problems and have limited dynamic range. Diode array spectroradiometers are not recommended for use in the ultraviolet range unless these specific problems are addressed.
1.4 The calibration described in this method employs the use of a standard of spectral irradiance. The standard of spectral irradiance values at given wavelengths for a specific input current and clearly defined measurement geometry. Uncertainties must also be known for the spectral irradiance values. The values assigned to this standard must be traceable to NIST. These standards may be obtained from a number of national standards laboratories and commercial laboratories. The spectral irradiance standards consist mainly of tungsten halogen lamps with coiled filaments enclosed in a quartz envelope, though other types of lamps are used. Standards can be obtained with calibration values covering all or part of the wavelength range from 200 to 4500 nm.
1.5 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 superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: G 138 – 96
Standard Test Method for
Calibration of a Spectroradiometer Using a Standard Source
of Irradiance
This standard is issued under the fixed designation G 138; 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 (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
A standardized means of performing and reporting calibration of the spectroradiometer for spectral
irradiance measurements is desirable.
This test method presents specific technical requirements for a laboratory performing calibration of
a spectroradiometer for spectral irradiance measurements. A detailed procedure for performing the
calibration and reporting the results is outlined.
This test method for calibration is applicable to spectroradiometric systems consisting of at least a
monochromator, input optics, and an optical radiation detector, and applies to spectroradiometric
calibrations performed with a standard of spectral irradiance with known irradiance values traceable
to the National Institute of Standards and Technology (NIST) or other national standards laboratory.
The standard must also have known uncertainties and measurement geometry associated with its
irradiance values.
1. Scope at given wavelengths for a specific input current and clearly
defined measurement geometry. Uncertainties must also be
1.1 This test method covers the calibration of spectroradi-
known for the spectral irradiance values. The values assigned
ometers for the measurement of spectral irradiance using a
to this standard must be traceable to NIST. These standards
standard of spectral irradiance that is traceable to NIST.
may be obtained from a number of national standards labora-
NOTE 1—Although NIST is referenced throughout this standard, it
tories and commercial laboratories. The spectral irradiance
should be assumed that other internationally recognized standards labo-
standards consist mainly of tungsten halogen lamps with coiled
ratories may be substituted.
filaments enclosed in a quartz envelope, though other types of
1.2 This method is not limited by the input optics of the
lamps are used. Standards can be obtained with calibration
spectroradiometric system. However, choice of input optics
values covering all or part of the wavelength range from 200 to
affects the overall uncertainty of the calibration.
4500 nm.
1.3 This method is not limited by the type of monochroma-
1.5 This standard does not purport to address all of the
tor or optical detector used in the spectroradiometer system.
safety concerns, if any, associated with its use. It is the
Parts of the method may not apply to determine which parts
responsibility of the user of this standard to establish appro-
apply to the specific spectroradiometer being used. It is
priate safety and health practices and determine the applica-
important that the choice of monochromator and detector be
bility of regulatory limitations prior to use.
appropriate for the wavelength range of interest for the
calibration. Though the method generally applies to photo- 2. Referenced Documents
diode array detector based systems, the user should note that
2.1 ASTM Standards:
these types of spectroradiometers often suffer from stray light
E 772 Terminology Relating to Solar Energy Conversion
problems and have limited dynamic range. Diode array spec-
E 1341 Practice for Obtaining Spectroradiometric Data
troradiometers are not recommended for use in the ultraviolet
from Radiant Sources
range unless these specific problems are addressed.
2.2 Other Documents:
1.4 The calibration described in this method employs the
CIE Publication No. 63
use of a standard of spectral irradiance. The standard of
NIST Technical Note 1927: Guidelines for Evaluation and
spectral irradiance must have known spectral irradiance values
Available from Secretary, U. S. National Committee, CIE, National Institute of
Standards and Technology, Gaithersburg, MD 20899.
This test method is under the jurisdiction of ASTM Committee G-3 on 3
Annual Book of ASTM Standards, Vol 12.02.
Durability of Nonmetallic Materials and is the direct responsibility of Subcommittee 4
Annual Book of ASTM Standards, Vol 06.01.
G03.09 on Solar and Ultraviolet Radiation Measurement Standards.
Current edition approved Jan. 10, 1996. Published March 1996.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G 138
Expressing Uncertainty of NIST Measurement Results 4.3 This method is generalized to allow for the use of
different types of monochromators provided that they can be
3. Terminology
configured for a bandwidth, wavelength range, and throughput
3.1 General terms pertaining to optical radiation and optical levels suitable for the calibration being performed.
4.4 This method is generalized to allow for the use of
measurement systems are defined in Terminology E 772. Some
of the more important terms from that standard used in this different types of optical radiation detectors provided that the
spectral response of the detector over the wavelength range of
paper are listed here.
3.2 bandwidth, n—the extent of a band of radiation reported the calibration is appropriate to the signal levels produced by
the monochromator.
as the difference between the two wavelengths at which the
amount of radiation is half of its maximum over the given
5. Apparatus
band.
5.1 Laboratory:
3.3 diffuser, n—a device used to scatter or disperse light
5.1.1 The room in which the calibrations are performed and
usually through the process of diffuse transmission or reflec-
especially the area surrounding the optical bench should be
tion.
devoid of reflective surfaces. The calibration values assigned to
3.4 integrating sphere, n—a hollow sphere coated internally
the spectral irradiance standard are for direct irradiance from
with a white diffuse reflecting material and provided with
the lamp and any radiation entering the monochromator from
separate openings for incident and exiting radiation.
some other source including ambient reflections will be a
3.5 irradiance, n—radiant flux incident per unit area of a
source of error.
surface.
5.1.2 The temperature and humidity in the laboratory shall
3.6 monochromator, n—an instrument for isolating narrow
be maintained so as to agree with the conditions under which
portions of the optical spectrum from a light source.
the calibrations of the spectral irradiance standard and the
3.7 polarization, n—with respect to optical radiation, the
calibration subsystems were performed (typically 25°C, 50 %
restriction of the magnetic or electric field vector to a single
relative humidity).
plane.
5.1.3 Air drafts in the laboratory should be minimized since
3.8 radiant flux, n—the time rate of flow of radiant energy
they could affect the output of electrical discharge lamps.
measured in watts.
5.2 Spectroradiometer:
3.9 spectral irradiance, n—irradiance per unit wavelength
5.2.1 Monochromator:
interval at a given wavelength.
5.2.1.1 This can be a fixed or scanning, single or multiple,
3.10 spectroradiometer, n—an instrument for measuring the
monochromator employing holographic or ruled gratings or
radiant energy of a light source at each wavelength throughout
prisms or a combination of these dispersive elements. For
the spectrum.
improved performance in the ultraviolet (uv) portion of the
3.11 ultraviolet, adj—optical radiation at wavelengths be-
spectrum, it is recommended that a scanning double mono-
low 400 nanometres.
chromator be used to achieve lower stray light levels (see Fig.
3.12 Definitions of Terms Specific to This Standard:
1). If the monochromator has interchangeable slits, it is
3.12.1 calibration subsystems, n—the instruments used to
important that the manufacturer document the effective band-
supply and monitor current to a standard lamp during calibra-
width of the monochromator with all possible combinations of
tion, consisting of a DC power supply, a current shunt, and a
the slits or that these bandwidths be determined experimen-
digital voltmeter.
tally. Configuration of the slits should be such that the
3.12.2 primary standard of spectral irradiance, n—a broad
bandpass function of the monochromator is symmetric, pref-
spectrum light source with known spectral irradiance values at
erably triangular. The bandwidth should be constant across the
various wavelengths which are traceable to NIST.
wavelength region of interest and maintained between 85 %
3.12.3 secondary standard of spectral irradiance, n—a
and 100 % of the measurement wavelength interval. The
standard calibrated by reference to another standard such as a
precision of the wavelength positioning of the monochromator
primary or reference standard.
should be 0.1 nm with an absolute accuracy of better than 0.5
4. Significance and Use nm (see Practice E 1341). For improved performance in the uv,
it is recommended that high order rejection filters be inserted in
4.1 This method is intended for use by laboratories perform-
the optical path in the monochromator. The purpose of the high
ing calibration of a spectroradiometer for spectral irradiance
order rejection filters is to block radiation in the monochroma-
measurements using a spectral irradiance standard of known
tor of unwanted wavelengths that could otherwise overpower
spectral irradiance values traceable to NIST, known uncertain-
the signals being measured. The effects of variations in
ties and known measurement geometry.
temperature and humidity on the performance of the mono-
4.2 This method is generalized to allow for the use of
chromator should be addressed in writing by the manufacturer.
different types of input optics provided that those input optics
5.2.1.2 Avoid mechanical shock and excessive vibration to
are suitable for the wavelength range and measurement geom-
the monochromator. This can be facilitated by the use of a
etry of the calibration.
vibration isolated lab table. If any optical parts in the mono-
chromator are configurable by the user, refer to the manufac-
turer precautions about opening the monochromator and han-
Available from American National Standards Institute, 11 West 42nd Street,
13th Floor, New York, NY 10036. dling any parts therein.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G 138
FIG. 1 Typical Double Grating Monochromator Layout
5.2.2 Optical Radiation Detector: is required. The input optics also can serve several other
5.2.2.1 The optical radiation detector employed by the important purposes.
spectroradiometer should be selected for optimal response over (1) Cosine Receptor—An ideal cosine receptor will accept
the wavelength range of interest. It is also important that the all radiation from an entire hemisphere and sample radiant flux
detector is sensitive enough to measure the levels of light that according to the cosine of the incident angle.
will be produced by the monochromator when it is configured (2) Depolarizer—The components in the monochromator
for the calibration process. The active area of the detector are unfavorably affected by polarized light. A depolarizer can
should be evenly illuminated by the exit slit of the monochro- produce more consistent results from light sources of any
mator. A photomultiplier is typically used because of its high polarization type.
responsivity and good signal-to-noise ratio. For this reason it is (3) Diffuser—A diffuser can remove hotspots from the
recommended for use when measuring spectral irradiance in incident radiation field and produce even illumination on the
the uv portion of the spectrum. entrance slit.
5.2.2.2 The effects of variation in temperature and humidity 5.2.4.2 Reflective input optics are more desirable than
on the response of the detector should be documented by the transmissive optics as they perform all three of the functions
manufacturer. Of all components of the spectroradiometer, the previously discussed and are generally more useful over larger
detector is usually the most sensitive to changes in tempera- wavelength ranges. It is important to take into account the
ture. Some detectors may require cooling in order to maintain amount of attenuation caused by the input optics as this will
a specific temperature. Avoid mechanical shock to the detector. affect the signal levels at the detector. Ensure that the input
If the detector requires an amplifier, any reported limitations optics are suitable for the wavelength range of interest. The
and uncertainties in the detector system must factor in the predominant choice of input optics is the integrating sphere.
contribution of the amplifier. 5.3 Optical Radiation Sources:
5.2.3 If a diode array based spectroradiometer system is 5.3.1 Wavelength Calibration Source:
used, note the following recommendations. 5.3.1.1 A stable wavelength source is required to calibrate
5.2.3.1 The diode array spectroradiometer should employ the wavelength positioning accuracy of the monochromator.
internal focusing optics in the monochromator. This can be a gas discharge lamp or a laser. The important thing
5.2.3.2 When measuring in the ultraviolet, stray light should is that the source have a known spectral emission line(s) of
be controlled by the use of high order rejection filters or narrow bandwidth.
internal baffling, or both. 5.3.1.2 If a laser source is used, occupants of the room
5.2.3.3 The diode array spectroradiometer should not be should wear eye protection appropriate for the class of laser.
used for measurements below 300 nm. Lasers should always be shielded from direct eye view.
5.2.4 Input Optics: 5.3.2 Standard of Spectral Irradiance:
5.2.4.1 Some means of collecting the incident radiation and 5.3.2.1 The spectral irradiance standard is a critical compo-
guiding it to evenly fill the entrance slit of the monochromator nent in the calibration process. This standard should be
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G 138
obtained from a national standards laboratory or a certified are of the same type and optical spectral distribution as the
commercial laboratory. It must have known spectral irradiance primary sta
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.