Reflectivity hemispherical spectral

A black body is defined as a body where all the incident radiation penetrates it and is completely absorbed within it. No radiation is reflected or allowed to pass through it. This holds for radiation of all wavelengths falling onto the body from all angles. In addition to this the black body is a diffuse radiator. Its spectral intensity LXs does not depend on direction, but is a universal function iAs(A,T) of the wavelength and the thermodynamic temperature. The hemispherical spectral emissive power MXs(X,T) is linked to Kirchhoff s function LXs(X,T) by the simple relationship... 

The fraction of the incident energy from all directions that is reflected into all directions at a particular wavelength is written as hemispherical spectral reflectivity. 

For an opaque surface, the relationship between the spectral hemispherical reflectivity and the spectral hemispherical absorptivity is... 

These definitions are for lolol hemispherical properties, since G represents the radiation flux incident on tlic surface from all directions over the hemi spherical space and over all wavelengths. Thus, a, p, and t are the average properties of a medium for all directions and all wavelengths. However, like einissivity, these properties can also be defined for a specific wavelength and/or direction. For example, the spectral directional absorptivity and spectral directional reflectivity of a surface are defined, respectively, as the absorbed and leflected fractions of the intensity of radiation incident at a specified wavelength in a specified direction as... 

Likewise, the spectral hemispherical absorptivity and. spectral hemispherical reflectivity of a surface arc defined as... 

Because of the reciprocity of the bidirectional reflectivity p", the hemispherical-directional spectral reflectivity for isotropic incident intensity pi, is equal to the directional-hemispherical reflectivity pi,. Here, a single prime ( ) is used to denote the directional nature of incident radiation. 

Dielectrics (insulating materials, with n = n2ln, and kx = k2 = 0) —Normal-hemispherical total or spectral reflectivity... 

Hendricks and Howell [253] measured the spectral normal transmittance and normal hemispherical reflectance of three sample thicknesses each of reticulated partially stabilized zirconia and silicon carbide at pore sizes of 10, 20, and 65 ppi. The measurements covered a spectral range of 400-500 nm. They used an inverse discrete ordinates method to find the spectrally dependent absorption and scattering coefficients as well as the constants appropri-... 

Specular reflection occurs when the angle of reflection equals the angle of incidence, whereas diffuse reflection is spread out evenly over a full hemisphere. The main difficulty in measuring the spectral transmittance properties of a kernel is the problem of collecting sufficient energy from the transmitted signal. To collect the maximum amount of light under such conditions the phototube should surround the entire sample. The nearest approach to this condition can be... 

Measured spectral hemispherical reflectance of uncoated (as received) and Ti02/Si02 double layer coated silicon solar cells. The approximate 7% reflectance at 700 nm results from silver metallization (—7% surface coverage). From Pettit et at. (33). 

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