SpectralEmissivity & Emittance

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Raytek’s Online Spectral Emissivity Guide

Screen Shot of Webpage

Santa Cruz CA, USA — As part of the IR Education section, the Raytek Corporation website contains some useful and well-presented information on Spectral Emissivity, one of the few instrument makers who do so.

Although they just call it plain “emissivity” they then present values for three or four different wavebands, according to the table viewed, “A Rose by any other name…”. There are two pages with disclaimers.

Here’s a summary of the opening statements and links to the actual data pages.Read More

Table of Emissivities in Three Popular Spectral Regions

The Table of Emissivity on the INFRAPOINT Messtechnik GmbH website, posted in 2009 (No longer available online) had summary data for a wide variety of materials broken down into three distinct spectral regions for the wavelength regions where the majority of infrared radiation thermometers and Infrared Thermal Imaging cameras operate.

First and second are tables that deal with the narrow spectral bands about 0.9 µm and 1.6 µm, the regions where many Silicon (Si) photovoltaic detectors (peak wavelength response: (0.9 µm) and both Germanium (Ge) and Indium Gallium Arsenide (InGaAs) (nominal wavelength region (0.7 – 1.6 µm) are used.

The third table cover the 8 – 14 µm waveband where most “low” (near ambient) temperature IR thermometers and thermal imaging sensors operate.

It has been reproduced here below in the spirit of Internet openness from our archives. We hope there is no problem in doing so and if any heir or assigns of INFRAPOINT Messtechnik GmbH wishes to keep this information secret, obviously against the original intent of INFRAPOINT, please contact us according to our webpage contact information.


   Table of emissivity        
  The emissivity ? (radiant emittance factor) is the relationship of the radiated intensity of a body to the intensity of a blackbody of the same temperature.
It is the most important factor, in order to determine of an item exactly.

If you want to measure the surface temperature with an infrared thermometer the emissivity must be known and correct adjusted
on the instrument.

               
   Material  Emissivity     Material  Emissivity  
  Metals Wavelength
0.9 µm 
Wavelength
1.6 µm 
  Non metals Wavelength
8 – 14 µm  
 
               
  Aluminium, bright 0.05 – 0.25  0.05 – 0.25    Asphalt  0.95   
  Aluminium, anodized 0.2 – 0.4  0.1 – 0.4    Concrete 0.95  
  Chrom, bright 0.28 – 0.32  0.25 – 0.3    Gypsum 0.85 – 0.95   
  Iron, oxidised 0.4 – 0.8 0.5 – 0.9    Graphite  0.75 – 0.92   
  Iron, not oxidised 0.35 0.1 – 0.3    Glass*, pane  0.80   
  Gold, bright 0.02 0.02    Rubber 0.85 – 0.95   
  Copper, bright 0.06 – 0.20 0.06 – 0.20    Wood, natural 0.8 – 0.95   
  Copper, oxidised  0.5 – 0.8  0.7 – 0.85    Chalk 0.98   
  Magnesium 0.03 – 0.8  0.05 – 0.3    Ceramics 0.85 – 0.95   
  Brass, bright  0.8 – 0.95  0.01 – 0.05    Plastics 0.85 – 0.95   
  Brass, oxidised  0.65 – 0.75  0.65 – 0.75    Masonry 0.85 – 0.95   
  Nickel, oxidised  0.8 – 0.9  0.4 – 0.7    Human skin 0.98   
  Platinum, black  –  0,95    Oil paints 0.85 – 0.95   
  Silver  0.02  0.02    Paper  0.85 – 0.95   
  Steel, melted 0.30  0.20 – 0.25    Porcelain 0.85 – 0.95   
  Steel, oxidised  0.8 – 0.9  0.8 – 0.9    Quartz  0.8   
  Steel, bright 0.40 – 0.45  0.30 – 0.4    Carbon black 0.95   
  Titanium, bright 0.5 – 0.75  0.3 – 0.5    Chamotte  0.85 – 0.95   
  Titanium, oxidised  –  0.6 – 0.8    Textile, Drapery 0.85 – 0.95   
  Zinc, bright 0.6  0.4 – 0.6    Tone 0.95   
  Zinc, oxidised  0.5  0.05    Water 0.95  
  Tin 0.25  0.1 – 0.3    Cement  0.9   
* The emissivity of glass (0.95 – 0.97 µm) is in the range of 4.5 – 7 µm particularly high.
Glass has there an absorption band (spectral range, where materials absorb radiation).
To measure glass surface temperatures, the best wavelength is at 5.14 µm, because
the measurement at this range is not affected by absorption bands such as carbon or hydrogen.

ET10 Reflectometer Measures Emissivity

San Diego CA, USA –Surface Optics’ ET10 measures emissivity values in two most commonly used spectral regions, 3 to 5 and 8 to 12 microns.

Its main application is to produce emissivity values for the infrared cameras.

Advanced IR cameras require the input of an emissivity value for accurate temperature calculations. The emissivity values obtained from tables can be far from real leading to large temperature uncertainties.

The ET10 can be used in the lab or in the field and on small or large objects. With the ET10 one can measure emissivity of any surface in just a few seconds.

Read More

Infrared Emission Spectroscopy of Polymer Reactions

Noninvasive Polymer Reaction Monitoring by Infrared Emission Spectroscopy with Multivariate Statistical Modeling
Randy J. Pell, James B. Callis, and Bruce R. Kowalski
Applied Spectroscopy, Vol. 45, Issue 5, pp. 808-818 (1991)

Abstract

“Infrared absorption and emission spectroscopy have been used to monitor the curing of a commercial paint product. Principal component analysis of the absorption data indicates that three factors are needed to explain the observed spectral/temporal variance. The interpretation of this finding in terms of changes in the physical state of the reaction mixture is discussed. A similar analysis of the emission data proved more difficult due to a nonlinear concentration/response relationship. A linearization step based on an approximate theoretical model is suggested. The absorption, linearized emittance, and raw emittance data are fit to a two-step sequential rate model using multivariate nonlinear optimization and error estimates derived by Monte Carlo calculations. Better agreement of the model parameters between the absorbance and emittance data is found after linearization, but it is found that linearization introduces large errors in the nonlinear parameter estimates. Comparisons of model parameters for the raw emittance data at different temperatures are made.”

Citation
R. J. Pell, J. B. Callis, and B. R. Kowalski, “Noninvasive Polymer Reaction Monitoring by Infrared Emission Spectroscopy with Multivariate Statistical Modeling,” Appl. Spectrosc. 45, 808-818 (1991)

Raytek’s Spectral Emissivity Table for Non-metals

The Raytek North America website includes a table for the emissivity of a large range of non-metallic materials that includes common building materials, ceramics, glasses and natural materials including ice & water in as many as four wavelength regions.

Wavebands covered include 1.0 micrometer (micron), 5.0 microns, 7.9 microns and the 8-14 micron band. No specific data and the limits of the various wavebands and there are many instances where the wavelength region is labelled as “nr” meaning “Not Recommended”.