Radiance/radiant flux

Radiance Radiant flux per unit solid angle (intensity) per unit area of an element of an extended source or reflecting surface in a specified direction. 

X-ray production by electron excitation, 5-9, 27, 28, 98-102, 176-179 X-ray radiance, definition, 6 X-ray radiant energy, definition, 6 X-ray radiant flux or power, definition, 6... 

The radiant flux

thermal radiation source through a spectrometer is calculated by multiplying the spectral radiance by the spectral optical conductance, the square of the bandwidth of the spectrometer, and the transmission factor of the entire system (Eq, 3.1-9). Fig. 3.3-1 shows the Planck function according to Eq. 3.3-3. The absorption properties of non-black body radiators can be described by the Bouguer-Lambert-Beer law ... 

The spectral radiance determines the exchange of thennal radiation energy. The radiant flux exchanged by a spectrometer or any other optical system with a spectral optical conductance Gp between two thennal radiators, A and B, is given by... 

Consider a beam of radiation of radiance L crossing a surface dS with the beam axis making an angle 0 to the normal to dS (Figure 4.6). dS projects as dS cos 0 perpendicular to the beam axis of the radiation, and the radiant flux density dF on dS is... 

The radiant flux density, or irradiance, on the surface dS is obtained by integrating the radiance over all angles ... 

FIGURE 4.6 Relation between radiance and radiant flux density. 

Sample radiance (L ) a differential quantity that is the reflected radiant flux per unit projected receiver solid angle per unit sample area. Note In practice is an average calculated from scattered power, P, collected by the projected receiver solid angle, 12 cos 0, from the illuminated area, A. The receiver aperture and distance from the sample determines Q and the angular resolution of the instrument ... 

Luminance is the intensity of emitted radiance per unit solid angle and frequency. It is sometimes called spectral radiance, or radiant flux. Emissivity is a property of a sample measured at standard conditions. The sample must be thick enough to be both optically opaque and smooth [63]. In the case of a perfect black body, the sample cannot be reflective. This property is not composition or geometry dependent even a heated pinhole cavity will show a good black body curve. 

The spectral radiance (p) is defined as the radiant power (or photon flux density) emitted per unit source area per unit sohd angle (conventionally expressed in W/m /sr). 

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