5.1 This standard does not purport to address the mean level of solar ultraviolet spectral irradiance to which materials will be subjected during their useful life. The spectral irradiance distributions have been chosen to represent a reasonable upper limit for natural solar ultraviolet radiation that ought to be considered when evaluating the behavior of materials under various exposure conditions.

5.2 Absorptance, reflectance, and transmittance of solar energy are important factors in material degradation studies. These properties are normally functions of wavelength, which require that the spectral distribution of the solar flux be known before the solar-weighted property can be calculated.

5.3 The interpretation of the behavior of materials exposed to either natural solar radiation or ultraviolet radiation from artificial light sources requires an understanding of the spectral energy distribution employed. To compare the relative performance of competitive products, or to compare the performance of products before and after being subjected to weathering or other exposure conditions, a reference standard solar spectral distribution is desirable.

5.4 A plot of the SMARTS2 model output for the reference hemispherical UV radiation on a 37° south facing tilted surface is shown in Fig. 1. The input needed by SMARTS2 to generate the spectrum for the prescribed conditions are shown in Table 1.

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 from sea 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

Specification for aerosol optical depth/turbidity input (0 = AOD at 500 nm): ITURB

9a

0.05

Aerosol Optical Depth at 500 nm: TAU5

10

38

Far field Spectral Albedo file to use (38 = Light Sandy Soil): IALBDX

10b

1

Specify tilt calculation (1 = yes): ITILT

10c

38 37 180

Albedo and Tilt variables—Albedo file to use for near field, Tilt, and Azimuth: IALBDG, TILT, WAZIM

11

280 400 1.0 1367.0

Wavelength Range—start, stop, mean radius vector correction, integrated solar spectrum irradiance: WLMN, WLMX, SUNCOR, SOLARC

12

2

Separate spectral output file print mode (2 = yes): IPRT

12a

280 400 0.5

Output file wavelength-Print limits, start, stop, minimum step size: WPMN, WPMX, INTVL

12b

1

Number of output variables to print: IOTOT

12c

8

Code relating output variables to print [8 = Hemispherical tilt, OUT(8)]

13

1

Circumsolar calculation mode (1 = yes): ICIRC

13a

0 2.9 0

Receiver geometry-Slope, View, Limit half angles: SLOPE, APERT, LIMIT

14

0

Smooth function mode (0 = none): ISCAN

15

0

Illuminance calculation mode (0 = none): ILLUM

16

0

UV calculation mode (0 = none): IUV

17

2

Solar Geometry mode (2 = Air Mass): IMASS

17a

1.05

Air mass value: AMASS

5.5 SMARTS2 Version 2.9.2 is required to generate AM 1.05 UV reference spectra.

5.6 The availability of the adjunct standard computer software (ADJG173CD⁵) for SMARTS2 allows one to (1) reproduce the reference spectra, using the above input parameters; (2) compute test spectra to attempt to match measured data at a specified FWHM, and evaluate atmospheric conditions; and (3) compute test spectra representing specific conditions for analysis vis-à-vis any one or all of the reference spectra.

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 provided 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 thickness.

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 (ADJG173CD³) to this standard) used to generate the standard spectra allows users to evaluate spectral differences relative to the spectra specified here.