ASTM C1549 Determination of Solar Reflectance

ASTM C1549 is used for the determination of solar reflectance near ambient temperature using a Portable Solar Reflectometer. It is used to determine the solar reflectance of flat opaque materials or coatings in a laboratory or in the field.

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ASTM C1549 Determination of Solar Reflectance

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM C1549 describes a portable solar reflectometer test method for measuring the solar reflectance, defined as the fraction of incident solar radiation reflected by a surface. Solar reflectance is a critical parameter for estimating heat absorption, surface temperature, and energy efficiency.

It provides reliable and comparable solar reflectance data for a wide range of materials to support material selection for energy-efficient buildings, heat management, and the mitigation of urban heat island effects.

Scope, Applications, and Benefits

Scope

ASTM C1549 outlines procedures for measuring the solar reflectance of flat, opaque materials under laboratory or field conditions using a portable solar reflectometer.
It evaluates:

Solar reflectance (albedo) values
Surface heat absorption potential
Reflective performance under different air mass conditions

The method applies to materials with diffuse and specular optical properties and is best suited for opaque surfaces.

Applications

Evaluation of roofing materials and cool roof systems
Assessment of pavements and urban infrastructure surfaces
Selection of coatings and surface finishes for energy efficiency
Urban planning and heat island mitigation strategies
Environmental and sustainability assessments

Benefits

Provides quick, non-destructive solar reflectance measurement
Supports energy-efficient material selection
Enables comparison of reflective performance across materials
Assists in reducing cooling loads and surface temperatures
Contributes to sustainable building and urban design

Test Process

Specimen Preparation

Flat, opaque specimens with a minimum dimension greater than 2.5 cm are prepared to fully cover the reflectometer measurement head.

Instrument Setup

A portable solar reflectometer with a measurement head, readout module, and connecting cable is configured for the required air mass values.

Measurement

The specimen is placed over the measurement head, and readings are taken for at least three 10-second cycles until stable values are obtained.

Data Collection

Multiple locations on the specimen are measured, and average solar reflectance values are recorded along with variability.

Technical Specifications

Parameter	Details
Test Principle	Measurement of reflected solar radiation using a portable reflectometer
Sample Type	Flat, opaque materials
Sample Area	Typically 150–300 cm²
Measured Output	Solar reflectance or absorptance (1 − reflectance)
Air Mass Values	0, 1, 1.5, and 2
Test Environment	Laboratory or outdoor conditions

Instrumentation Used for Testing

Portable solar reflectometer
Measurement head with radiation source and detector
Digital readout module
Connecting cables
Data logging or averaging software

Results and Deliverables

Solar reflectance values for tested materials
Average reflectance with standard deviation
Air mass conditions used during measurement
Surface description of the specimen
Comparative data for material selection and energy analysis

Frequently Asked Questions

Several methods are available to measure solar reflectance; the most used is ASTM 903-12, which covers measuring solar reflectance of materials using a spectrophotometer equipped with an integrating sphere.

An SRI value is calculated using the roof surface's Solar Reflectance (SR) and Thermal Emittance (TE).

Both specular and hemispherical reflectance can be measured with spectrophotometers depending on the accessory used.

Solar reflectance or reflectivity is the ability of a material to reflect solar energy from its surface into the atmosphere. Emissivity is a material's ability to release absorbed energy. SRI indicates how hot a material is likely to become when its surface comes into contact with solar radiation.