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.

Handbook of OSML Libraries: Emittance

CRMHT – CNRS Centre de Recherche sur les Matériaux à Haute Température, Orléans, France
Mesure indirecte de l’émittance (Includes sample data for Silicon Dioxide)

Mesure de la réflectivité et de la transmissivité normales spectrales (10 à 40 000 cm-1 soit 1 000 à 0,25 µm).

L’émissivité normale spectrale se déduit indirectement par calcul de ces deux grandeurs par application des lois de Kirchhoff ,

i.e. at each wavelength, Emissivity =1 – Reflectivity – Transmissity

Emittance-WN Handbook of OSML Libraries
E – dielectric function
N – complex refractive index
RT – reflectivity, layer transmissivity
WN – wave number
OSML Source : [Emitttance-WN]
Function Group : [Optical Functions]
Emittance-E
Emittance-E (AE) represents the fraction of the incident radiation that is absorbed (Kirchhoff law) by a sample with a plate shape. Its expression take into account for multiple reflections (no interference effects) and depends on the dielectric functions of the incident medium Ei, those of the material Eo and the thickness d of the sample.
Function signature : Emittance-E(x,Ei,Eo,Thickness)Units


The spectral dependence must be expressed in wave numbers (cm-1) and the thickness in (cm).
Emittance-N
Emittance-N (AN) represents the fraction of the incident radiation that is absorbed (Kirchhoff law) by a sample with a plate shape. Its expression take into account for multiple reflections (no interference effects) and depends on the complex refractive indexes of the incident medium Ni, those of the material No and the thickness d of the sample.
Function signature : Emittance-N(x,Ni,No,Thickness)Units


The spectral dependence must be expressed in wave numbers (cm-1) and the thickness in (cm).
Emittance-RT
Emittance-RT (ART) represents the fraction of the incident radiation that is absorbed (Kirchhoff law) by a sample with a plate shape. Its expression take into account for multiple reflections (no interference effects and depends on the reflectivity R and the layer transmissivity T of the sample.
Function signature : Emittance-RT(R,T)
Planck-WN
Planck-WN (PWN) is the wave number version of the Planck function. Its expression depends on the temperature T.
Function signature : Planck-WN(x,T)
Constants : C1=1.1910 10-6 (W.m2) C2=1.4388 (cm.K)

See Also : [Optical Functions] [Reflectance-WN] [Transmittance-WN]

Handbook of OSML Libraries

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

Polarized spectral emittance from periodic micromachined surfaces. II. Doped silicon: Angular variation

PJ Hesketh, JN Zemel, B Gebhart – Physical Review B, 1988 – APS Polarized spectral emittance from periodic micromachined surfaces. II. VOLUME 37, NUMBER 18

From the Abstract:The polarized directional spectral (3 um <=lambda =>14um) emittances (PDSE’s) of highly doped, micromachined, periodic structures on silicon were measured…