ASTM G177-03
(Specification)Standard Tables for Reference Solar Ultraviolet Spectral Distributions: Hemispherical on 37 Tilted Surface
Standard Tables for Reference Solar Ultraviolet Spectral Distributions: Hemispherical on 37 Tilted Surface
SCOPE
1.1 The table provides a standard ultraviolet spectral irradiance distribution that maybe employed as a guide against which manufactured ultraviolet light sources may be judged when applied to indoor exposure testing. The table provides a reference for comparison with natural sunlight ultraviolet spectral data. The ultraviolet reference spectral irradiance is providded for the wavelength range from 280 to 400 nm. The wavelength region selected is comprised of the UV-A spectral region from 320 to 400 nm and the UV-B region from 280 to 320 nm.
1.2 The table defines a single ultraviolet solar spectral irradiance distribution:
1.2.1 Total hemispherical ultraviolet solar spectral irradiance (consisting of combined direct and diffuse components) incident on a sun-facing, 37 tilted surface in the wavelength region from 280 to 400 nm for air mass 1.05, at an elevation of 2 km (2000 m) above sea level for the United States Standard Atmosphere profile for 1976 (USSA 1976), excepting for the ozone content which is specified as 0.30 atmosphere-centimeters (atm-cm) equivalent thichkness.
1.3 The data contained in these tables were generated using the SMARTS2 Version 2.9.2 atmospheric transmission model developed by Gueymard (1,2).
1.4 The climatic, atmospheric and geometric parameters selected reflect the conditions to provide a realistic maximum ultraviolet exposure under representative clear sky conditions.
1.5 The availability of the SMARTS2 model (as an adjunct to this standard) used to generate the standard spectra allows users to evaluate spectral differences relative to the spectra specified here.
General Information
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Standards Content (Sample)
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Designation: G 177 – 03
Standard Tables for
Reference Solar Ultraviolet Spectral Distributions:
Hemispherical on 37° Tilted Surface
This standard is issued under the fixed designation G177; 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.
e NOTE—The reference to ADJG173CD was added editorially in March 2006.
INTRODUCTION
These tables of solar ultraviolet (UV) spectral irradiance values have been developed to meet the
need for a standard ultraviolet reference spectral energy distribution to be used as a reference for the
upper limit of ultraviolet radiation in the outdoor weathering of materials and related indoor exposure
studies.Awide variety of solar spectral energy distributions occur in the natural environment and are
simulatedbyartificialsourcesduringproduct,material,orcomponenttesting.Tocomparetherelative
opticalperformanceofspectrallysensitiveproducts,ortocomparetheperformanceofproductsbefore
and after being subjected to weathering or other exposure conditions, a reference standard solar
spectral distribution is required. These tables were prepared using version 2.9.2 of the Simple Model
oftheAtmosphericRadiativeTransferofSunshine(SMARTS2)atmospherictransmissioncode(1,2).
SMARTS2 uses empirical parameterizations of version 4.0 of theAir Force Geophysical Laboratory
(AFGL) Moderate Resolution Transmission model, MODTRAN (3,4). An extraterrestrial spectrum
differing only slightly from the extraterrestrial spectrum in ASTM E490 is used to calculate the
resultant spectra. The hemispherical (2p steradian acceptance angle) spectral irradiance on a panel
tilted 37° (average latitude of the contiguous United States) to the horizontal is tabulated. The
wavelengthrangeforthespectraextendsfrom280to400nm,withuniformwavelengthintervals.The
input parameters used in conjunction with SMARTS2 for each set of conditions are tabulated. The
SMARTS2 model and documentation are available as an adjunct (ADJG0173CD )to this standard.
1. Scope wavelength region selected is comprised of the UV-Aspectral
region from 320 to 400 nm and the UV-B region from 280 to
1.1 The table provides a standard ultraviolet spectral irradi-
320 nm.
ance distribution that maybe employed as a guide against
1.2 The table defines a single ultraviolet solar spectral
which manufactured ultraviolet light sources may be judged
irradiance distribution:
when applied to indoor exposure testing. The table provides a
1.2.1 Total hemispherical ultraviolet solar spectral irradi-
reference for comparison with natural sunlight ultraviolet
ance (consisting of combined direct and diffuse components)
spectral data. The ultraviolet reference spectral irradiance is
incident on a sun-facing, 37° tilted surface in the wavelength
providded for the wavelength range from 280 to 400 nm. The
regionfrom280to400nmforairmass1.05,atanelevationof
2 km (2000 m) above sea level for the United States Standard
ThesetablesareunderthejurisdictionofASTMCommitteeG03onWeathering
Atmosphere profile for 1976 (USSA 1976), excepting for the
and Durability and is the direct responsibility of Subcommittee G03.09 on
ozone content which is specified as 0.30 atmosphere-
Radiometry.
centimeters (atm-cm) equivalent thichkness.
Current edition approved Sept. 10, 2003. Published November 2003.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
1.3 The data contained in these tables were generated using
this standard.
the SMARTS2 Version 2.9.2 atmospheric transmission model
Available from ASTM International Headquarters. Order Adjunct No.
developed by Gueymard (1,2).
ADJG173CD.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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G177–03
dE
1.4 The climatic, atmospheric and geometric parameters
E 5 (2)
l
dl
selected reflect the conditions to provide a realistic maximum
ultraviolet exposure under representative clear sky conditions.
3.2.6 spectral passband—the effective wavelength interval
1.5 The availability of the SMARTS2 model (as an adjunct
within which spectral irradiance is allowed to pass, as through
(ADJG0173CD )tothisstandard)usedtogeneratethestandard
a filter or monochromator. The convolution integral of the
spectra allows users to evaluate spectral differences relative to
spectral passband (normalized to unity at maximum) and the
the spectra specified here.
incident spectral irradiance produces the effective transmitted
irradiance.
2. Referenced Documents
3.2.6.1 Discussion—Spectralpassbandmayalsobereferred
toasthespectralbandwidthofafilterordevice.Passbandsare
2.1 ASTM Standards:
usually specified as the interval between wavelengths at which
E490 Standard Solar Constant and Zero Air Mass Solar
one half of the maximum transmission of the filter or device
Spectral Irradiance Tables
occurs, or as full-width at half-maximum, FWHM.
E772 Terminology Relating to Solar Energy Conversion
2.2 ASTM Adjunct: 3.2.7 spectral interval—the distance in wavelength units
ADJG0173CD Simple Model for Atmospheric Transmis- between adjacent spectral irradiance data points.
sion of Sunshine 3.2.8 spectral resolution—the minimum wavelength differ-
ence between two wavelengths that can be identified unam-
3. Terminology biguously.
3.2.8.1 Discussion—In the context of this standard, the
3.1 Definitions—Definitions of terms used in this specifica-
spectral resolution is simply the interval, Dl, between spectral
tion not otherwise described below may be found inTerminol-
data points, or the spectral interval.
ogy E772.
3.2.9 total precipitable water—the depth of a column of
3.2 Definitions of Terms Specific to This Standard:
water (with a section of 1 cm ) equivalent to the condensed
3.2.1 air mass zero (AM0)—describes solar radiation quan-
water vapor in a vertical column from the ground to the top of
tities outside the Earth’s atmosphere at the mean Earth-Sun
the atmosphere. (Unit: cm or g/cm )
distance (1 Astronomical Unit). See ASTM E490.
3.2.10 total ozone—the depth of a column of pure ozone
3.2.2 integrated irradiance E —spectral irradiance in-
l1−l2
equivalent to the total of the ozone in a vertical column from
tegrated over a specific wavelength interval from l to l ,
1 2
-2
thegroundtothetopoftheatmosphere.(Unit:atmosphere-cm)
measured in W·m ; mathematically:
3.2.11 wavenumber—a unit of frequency, y, in units of
l2
-1
E 5 E dl (1)
* reciprocal centimeters (symbol cm ) commonly used in place
l12l2 l
l1
of wavelength, l. The relationship between wavelength and
3.2.3 solar irradiance, hemispherical E —onagivenplane,
H
frequency is defined by ly = c, where c is the speed of light in
thesolarradiantfluxreceivedfromthewithinthe2-psteradian
vacuum.Toconvertwavenumbertonanometers, l·nm=1·10 /
field of view of a tilted plane from the portion of the sky dome
-1
y·cm .
and the foreground included in the plane’s field of view,
including both diffuse and direct solar radiation.
4. Technical Basis for the Tables
3.2.3.1 Discussion—For the special condition of a horizon-
4.1 These tables are modeled data generated using an air
tal plane the hemispherical solar irradiance is properly termed
mass zero (AM0) spectrum based on the extraterrestrial spec-
global solar irradiance, E . Incorrectly, global tilted, or total
G
trumofofGueymard(1,2)derivedfromKurucz(5),theUnited
global irradiance is often used to indicate hemispherical
States StandardAtmosphere of 1976 (USSA) referenceAtmo-
irradiance for a tilted plane. In case of a sun-tracking receiver,
sphere (6), the Shettle and Fenn RuralAerosol Profile (7), the
this hemispherical irradiance is commonly called global nor-
SMARTS2 V. 2.9.2 radiative transfer code. Further details are
mal irradiance. The adjective global should refer only to
provided in X1.3.
hemispherical solar radiation on a horizontal, not a tilted,
4.2 The 37° tilted surface was selected as it represents the
surface.
average latitude of the contiguous forty-eight states of the
3.2.4 aerosol optical depth (AOD)—the wavelength-
continental U.S., and outdoor exposure testing often takes
dependent total extinction (scattering and absorption) by aero-
place at latitude tilt.
sols in the atmosphere. This optical depth (also called “optical
4.3 The documented USSA atmospheric profiles utilized in
thickness”) is defined here at 500 nm.
the MODTRAN spectral transmission model (6) have been
3.2.4.1 Discussion—See X1.1.
used to provide atmospheric properties and concentrations of
3.2.5 solar irradiance, spectral E —solar irradiance E per
l
absorbers.
unit wavelength interval at a given wavelength l. (Unit: Watts
-2 -1
4.4 The SMARTS model Version 2.9.2 is available at
per square meter per nanometer, W·m ·nm )
Internet URL: http://rredc.nrel.gov/solar/models/SMARTS.
4.5 To provide spectral data with a uniform spectral step
size,theAM0spectrumusedinconjunctionwithSMARTS2to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
generate the terrestrial spectrum is slightly different from the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ASTM extraterrestrial spectrum, ASTM E 490. Because
StandardsvolumeInformation,refertothestandard’sDocumentSummaryPageon
the ASTM website. ASTM E490 and SMARTS2 both use the data of Kurucz (5),
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G177–03
the SMARTS2 and E490 spectra are in excellent agreement duce the reference spectra, using the above input parameters;
although they do not have the same spectral resolution. (2) compute test spectra to attempt to match measured data at
4.6 The current spectra reflect improved knowledge of a specified FWHM, and evaluate atmospheric conditions; and
atmosphericaerosolopticalproperties,transmissionproperties, (3) compute test spectra representing specific conditions for
and radiative transfer modeling (8). analysis vis-à-vis any one or all of the reference spectra.
4.7 The terrestrial solar spectral in the tables have been
computed with a spectral bandwidth equivalent to the spectral
6. Solar Spectral Irradiance
resolution of the tables, namely 0.5 nm.
6.1 Table 2 presents the reference spectral irradiance data
global hemispherical solar irradiance on a plane tilted at 37°
5. Significance and Use
toward the equator, for the conditions specified in Table 1.
5.1 Thisstandarddoesnotpurporttoaddressthemeanlevel
6.2 The table contains:
of solar ultraviolet spectral irradiance to which materials will
6.2.1 Hemispherical solar spectral irradiance incident on an
be subjected during their useful life. The spectral irradiance
equator-facing plane tilted to 37° from the horizontal in the
distributions have been chosen to represent a reasonable upper
wavelength range from 280 to 400 nm.
limit for natural solar ultraviolet radiation that ought to be
6.2.2 The columns in each table contain:
considered when evaluating the behavior of materials under
6.2.2.1 Column 1: Wavelength in nanometers (nm).
various exposure conditions.
6.2.2.2 Column 2: Mean hemispherical spectral irradiance
-2
5.2 Absorptance, reflectance, and transmittance of solar
incident on surface tilted 37° toward the equator. E ,W·m ·
l
energy are important factors in material degradation studies. -1
nm .
These properties are normally functions of wavelength, which
require that the spectral distribution of the solar flux be known
7. Validation
before the solar-weighted property can be calculated.
7.1 Inpartofthespectralregionofinterest,(295to400nm)
5.3 The interpretation of the behavior of materials exposed
the SMARTS2 model has been verified against experimental
to either natural solar radiation or ultraviolet radiation from
data. SMARTS2 performance is adequate for the region from
artificiallightsourcesrequiresanunderstandingofthespectral
295 to 400 nm. No reliable experimental data has been found
energy distribution employed. To compare the relative perfor-
to verify performance below 295 nm.
manceofcompetitiveproducts,ortocomparetheperformance
7.2 Comparisons of the SMARTS2 computer model with
of products before and after being subjected to weathering or
bothMODTRANmodelresultsandmeasuredspectraldataand
other exposure conditions, a reference standard solar spectral
other rigorous spectral models are reported in (1,2). Fig. 2 is a
distribution is desirable.
plot of the relative magnitude of the spectral differences
5.4 Aplot of the SMARTS2 model output for the reference
observed between MODTRAN version 4.0 and SMARTS2 for
hemisphericalUVradiationona37°southfacingtiltedsurface
identical conditions. Results indicate that the various models
isshowninFig.1.TheinputneededbySMARTS2togenerate
are within ~5% in spectral regions where significant energy is
the spectrum for the prescribed conditions are shown in Table
present.
1.
7.3 Comparison of these reference spectra with clear sky
5.5 SMARTS2 Version 2.9.2 is required to generate AM
solarspectralirradiancedatafromvariousspectrometersunder
1.05 UV reference spectra.
variousatmosphericconditionsapproximatingthosechosenfor
5.6 The availability of the adjunct standard computer soft-
5 this data are in reasonable agreement (8).
ware (ADJG0173CD ) for SMARTS2 allows one to (1) repro-
8. Keywords
8.1 global hemispherical; materials exposure; terrestrial;
South facing for the northern hemisphere, north facing for the southern
hemisphere. ultraviolet solar spectral irradiance
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G177–03
FIG. 1 Total Hemispherical Ultraviolet Reference Spectra Based on SMARTS2 Runs for AM1.05 UV Spectral Profile (a) Linear Scale; (b)
Logarithmic Scale
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G177–03
TABLE 1 SMARTS Version 2.9.2 Input File to Generate the Reference Spectra
Card ID Value Parameter/Description/Variable Name
1 ’ASTM UV_Std_Spectra’ Header
2 1 Pressure input mode (1 = pressure and altitude): ISPR
2a 820.0 2.0. Station Pressure (mb) and altitude (km): SPR, ALT
3 1 Standard Atmosphere Profile Selection (1 = use default
atmosphere): IATM1
3a ’USSA’ Default Standard Atmosphere Profile: ATM
4 1 Water Vapor Input (1 = default from Atmospheric Profile): IH2O
5 0 Ozone Calculation (0 = user input concentariont and altitude): IO3
5a 1 0.3 Ozone Atltitude correctiom (IALT =1=>correct fromsea level),
Ozone Concentration (AbO3 = 0.30 atm cm)
6 1 Pollution level mode (1 = standard conditions/no pollution): IGAS
(see X1.3)
7 370 Carbon Monoxide volume mixing ratio (ppm): qCO2 (see X1.3)
7a 1 Extraterrestrial Spectrum (1 = SMARTS/Gueymard): ISPCTR
8 ’S&F_RURAL’ Aerosol Profile to Use: AEROS
9 0 Specific
...
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