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A free resource about Spectral Emissivity & Spectral Emittance, the important optical properties of matter used in Thermal Infrared Thermography and Thermal Radiation Thermometry.


Learn about emissivity basics & why Total Emissivity is the wrong parameter for Thermal Infrared Imaging & Thermometry on our 2003 Emissivity Trail Page.


Learn from Success. Why re-invent the wheel? IR Thermography & Thermometry have been used for many years, but poorly described. Here's a database of successes!

AZ Technology Optical Properties Instrumentation

AZ Technology is an industry leader in measuring the Optical Properties of materials.

All measurements are made with the finest instruments on the market. AZ Technology specializes in the measurement of solar absorption,emittance, reflectance, and transmittance.

Optical properties measurements are made with the following instruments:

The SpectraFIRE measures near normal reflectance directly and the emittance is calculated from the reflectance measurements. SpectraFIRE has the following specification:

32 wave numbers (cm-1); selectable down to 4 cm-1.

Reflectance Repeatability:
2.5 – 16um± 1%
16 – 25um± 1.5%
25 – 40um± 2%

Spectral Resolution:
2.5 to > 40um

The LPSR 200IR measures total hemispherical spectral reflectance directly and solar absorption, transmittance, or emittance is calculated from the reflectance measurements.The LPSR 200IR has the following specification:

250 to 2800nm

Spectral Resolution with Automatic Slit Control:
250-2500nm better than 5% of wavelength
2500-2800nm better than 8% of wavelength

250 to 2500nm±1%
2500 to 2800nm – ±2%

AZ Technology Corporation
7047 Old Madison Pike, Suite 300
Huntsville, AL 35806 USA

Tel: +1 256.837.9877

FAX: +1 256.837.1155

ASTM E307-72(2002)

ASTM E307-72(2002):

Standard Test Method for Normal Spectral Emittance at Elevated Temperatures

Developed by Subcommittee: E21.04

Book of Standards Volume: 15.03
“1. Scope

“1.1 This test method describes a highly accurate technique for measuring the normal spectral emittance of electrically conducting materials or materials with electrically conducting substrates, in the temperature range from 600 to 1400 K, and at wavelengths from 1 to 35 ?m.

“1.2 The test method requires expensive equipment and rather elaborate precautions, but produces data that are accurate to within a few percent. It is suitable for research laboratories where the highest precision and accuracy are desired, but is not recommended for routine production or acceptance testing. However, because of its high accuracy this test method can be used as a referee method to be applied to production and acceptance testing in cases of dispute.

“1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.

“1.4 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.”




Personal Author(s) : Harrison, William N. ; Richmond, Joseph C. ; Shorten, Frederick J. ; Joseph, Horace M.

Handle / proxy Url :

Report Date : NOV 1963

Pagination or Media Count : 99

Abstract: Equipment and procedures were developed to measure normal spectral emittance of specimens that can be heated by passing a current through them, at temperatures in the range of 800 to 1400 K, and over the wavelength range of 1 to 15 microns. A data-processing attachment for the normal spectral emittance equipment was designed to (1) automatically correct the measured emittance for ‘100% line’ and ‘zero line’ errors on the basis of previously-recorded calibration tests; (2) record the corrected spectral emittance values and wavelengths at preselected wavelength intervals on punched paper tape in form suitable for direct entry into an electronic digital computer; and (3) to compute during a spectral emittance test on a specimen the total normal emittance, or absorptance for radiant energy of any known spectral distribution of flux, of the specimen. Working standards of normal spectral emittance having low, intermediate and high emittance values, respectively, were prepared and calibrated for use in other laboratories to check the operation of equipment and procedures used for measuring normal spectral emittance.

Spectral Emittance…Ash-Like Deposits

Spectral Emittance of Particulate Ash-Like Deposits: Theoretical Predictions Compared to Experimental Measurement, Journal of Heat Transfer — April 2004 — Volume 126, Issue 2, pp. 286-289

S. P. Bhattacharya

Cooperative Research Centre for Clean Power from Lignite, 8/677 Springvale Road, Mulgrave, Victoria 3170, Australia
(Received September 11, 2002; revised July 1, 2003)

From  the Abstract: “This note presents results of a theoretical and experimental investigation on the emittance of particulate deposits.”

Source Abstract

Cool Roofing Samples (Emittance)

The Heat Island Group at Lawrence Berkeley National Laboratory, Berkeley, CA have measured solar reflectance of roofing samples with an UV-VIS-NIR Spectrometer with an integrating sphere and they measured the spectral emittance of the samples with a FTIR Spectral Emissometer. The following writeup and graphs are from their webpageat

“Below are examples of complete reflectance and emittance data for several metal roofing samples made of cool roofing materials. These measurements show examples of complete laboratory information needed to determine radiative heat exchange by a roof which, in turn, can be used to estimate peak roof temperatures.

“The spectral solar reflectance is the total reflectance (diffuse and specular) as a function of wavelength, across the solar spectrum (wavelengths of 0.3 to 2.5 µm). It is used to compute the overall solar reflectance, using a standard solar spectrum as a weighting function. It also contains the information in the visual range (0.4 to 0.7 µm) which is sufficient to compute the color coordinates for color matching with other materials.

“The spectral thermal emittance (the graphs on the right) contains the information for computing the overall thermal emittance, using a blackbody curve as the weighting function. The spectral range is about 5 to 40 µm. If the spectral thermal emittance is approximately a horizontal line (a “gray” body), then the overall emittance is adequate for computing longwave radiative radiative exchange between the roof and the atmosphere. If the spectral thermal emittance deviates markedly from a horizonal line, then the details of the spectral emittance and the atmospheric emittance are necessary for a complete computation.

Note that the hunter green sample (middle graph) looks green to the eye because of the reflectance “bump” at 0.5 µm. The average solar reflectance, at 0.086, is almost as low as black (zero).””The burgundy sample (bottom graph) looks red due to the increase in reflectance near 0.7 µm. The visible reflectance is only about 0.1, but the relatively high reflectance in the near infrared (0.7 to 2.5 µm) yields an overall solar reflectance of 0.226.”The emittance for all these samples is roughly 0.9, with an abrupt fall-off near 6 µm. Link to: Roof Heat Transfer > Emittance”
Galvalume (top graph), due to the inclusion of aluminum metal in the zinc anti-corrosion coating, is more reflective to sunlight than traditional galvanized steel which has a solar reflectance around 0.5.A further coating, with a clean acrylic material (low graph), can be used to raise the infrared emittance without significantly changing the solar reflectance.