ASTM E903-20 PDF

Full title and description

ASTM E903-20 — Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres. This test method specifies procedures for measuring spectral absorptance, reflectance, and transmittance of materials using spectrophotometers equipped with integrating spheres and for computing solar‑weighted properties from the measured spectra.

Abstract

ASTM E903-20 defines measurement practice and data reduction for near‑normal hemispherical spectral reflectance/transmittance using integrating‑sphere spectrophotometers. Results are commonly reported as spectral curves and as solar‑weighted values (using a reference solar spectrum), over a broad near‑UV to short‑wave‑IR range typically covering about 300 nm to 2500 nm. The method addresses instrumentation, sample handling, measurement geometry, calculation of solar‑weighted absorptance/reflectance/transmittance, and known limitations for textured or inhomogeneous specimens.

General information

• Status: Active standard (current edition).
• Publication date: 2020 (E903-20; ASTM store notes last update Oct 21, 2020).
• Publisher: ASTM International (formerly American Society for Testing and Materials).
• ICS / categories: ICS 77.140.80 (as shown on the ASTM record).
• Edition / version: E903-20 (2020 revision).
• Number of pages: 17 pages (format and pagination as published by ASTM).

(Publication and bibliographic details based on the ASTM product record.)

Scope

This test method covers spectral measurement of absorptance, reflectance, and transmittance of materials using spectrophotometers equipped with integrating spheres; it includes methods for computing solar‑weighted properties from measured spectra. The procedure is intended for materials that exhibit both specular and diffuse behavior and is commonly applied using standard reference solar spectral irradiances (e.g., G173) to derive solar‑weighted numbers. The method notes special considerations or reduced applicability for textured, patterned, corrugated, or strongly inhomogeneous specimens, and for polarizing samples.

Key topics and requirements

• Instrumentation: integrating‑sphere spectrophotometer (typical sphere ≥150 mm), recommended double‑beam configuration and suitable light sources for 300–2500 nm measurements.
• Spectral range and data: acquisition of spectral reflectance/transmittance (near‑UV to SWIR) and use of a solar spectral irradiance weighting function to compute solar‑weighted absorptance/reflectance/transmittance.
• Measurement geometry: near‑normal illumination with hemispherical collection (near‑normal hemispherical reflectance/transmittance conventions used by the standard).
• Sample preparation and size: requirements that specimens be large enough to cover sphere/sample apertures; guidance on coatings and handling textured or patterned surfaces.
• Data reduction and reporting: instructions for converting spectral data to solar‑weighted properties, reporting uncertainty, and noting the reference solar spectrum used.
• Limitations and uncertainty: cautions for textured, inhomogeneous, or polarizing samples and recommendations to characterize measurement uncertainty and instrument calibration.

Typical use and users

ASTM E903-20 is used by test laboratories, materials manufacturers (coatings, roofing, glazing, films), solar‑energy researchers, certification bodies (e.g., cool‑roof rating programs), and code authorities to determine and compare radiative properties relevant to thermal performance, energy modeling, durability studies, and spacecraft thermal control. Its outputs feed product ratings (solar reflectance, transmittance), building energy calculations, and research on urban heat island mitigation.

Related standards

Standards commonly referenced with or used alongside E903 include: ASTM G173 (reference solar spectral irradiances), ASTM E1084 / E1175 (large‑sphere methods for certain specimen types), ASTM E971 (calculation practices), ASTM C1549 (portable solar reflectometer field method), ASTM E1980 (solar reflectance index practice), and other spectrophotometer practices and reference material guidelines used for calibration and uncertainty estimation.

Keywords

solar absorptance, solar reflectance, solar transmittance, integrating sphere, spectrophotometer, spectral measurement, solar‑weighted, specular, diffuse, near‑normal hemispherical, G173, SRI.

FAQ

Q: What is this standard?

A: ASTM E903-20 is a standardized test method that defines how to measure spectral solar absorptance, reflectance, and transmittance of materials using integrating‑sphere spectrophotometers and how to compute solar‑weighted properties from those spectra.

Q: What does it cover?

A: It covers instrumentation and measurement procedures for spectral reflectance and transmittance (commonly across roughly 300–2500 nm), sample handling, calculation of solar‑weighted values using a reference solar spectrum, reporting, and notes on applicability and limitations (for textured, patterned, or polarizing samples).

Q: Who typically uses it?

A: Accredited test labs, manufacturers of coatings/roofing/glass/films, building code and rating programs, researchers in solar energy and materials science, and agencies evaluating thermal or optical performance use E903 measurements for product specification, compliance, and research.

Q: Is it current or superseded?

A: The current published revision is E903-20 (2020). The standard is active in the ASTM catalog; users should confirm any later revisions directly with ASTM if they need the absolute latest edition.

Q: Is it part of a series?

A: E903 is part of the ASTM suite of solar/optical test methods maintained by Committee E44 and is commonly used alongside related practices and test methods (for example, E1084/E1175, E971, E1980, and G173). These complementary documents address alternative measurement geometries, calculation practices, or reference solar spectra.

Q: What are the key keywords?

A: Solar absorptance, solar reflectance, solar transmittance, integrating sphere, spectrophotometer, spectral, solar‑weighted, specular, diffuse, G173, SRI.