Radiation properties of real surface

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The characteristics of the blackbody are independent of material properties, because the blackbody is an idealization that can only be approached in reality, and its emission properties depend only on the independent parameters T and λ or their product. Real materials will absorb (and therefore emit) less thermal radiation than predicted for a blackbody. To account for the differences between the ideal blackbody and the performance of real materials, the radiative properties of opaque surfaces are now introduced. These properties show how the real material behaves in its ability to emit, absorb, and reflect radiation relative to a blackbody.


Opaque Surface Property Definitions

The radiative properties are usually expressed as surface properties, although on a microscopic basis radiation incident on a surface may actually penetrate for some distance into the bulk material. We found that emitted or absorbed intensity is independent of angle for the blackbody; however, the surface properties of real materials are angularly dependent; i.e., the intensity emitted by a real surface may vary with respect to the angle relative to the surface normal, as does the ability of the surface to absorb radiation.

See Main Article Opaque Surface Property Definitions

Predictions of real surface properties for radiation

Although the radiative properties for many materials have been measured, there are still many others for which no data are available. For some classes of opaque materials, it is possible to predict the spectral, directional, total and hemispherical properties through the use of electromagnetic theory. These predictions have limitations in accuracy and applicability, but serve in the absence of other data.

See Main Article Predictions of real surface properties for radiation


Faghri, A., Zhang, Y., and Howell, J. R., 2010, Advanced Heat and Mass Transfer, Global Digital Press, Columbia, MO.

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