3.1.2.2 Reflection Qualities of Materials The reflection properties of the structure surfaces are provided in this 4 5 6 section in graphical format. ’ * The wavelength dependence of the reflectivity for the various materials are contained in Figures 14 - 20. The roughness of the reflecting surface will also influence the intensity of light at some given angular location. A truly specular reflection will retain the character of the incident beam, but a strictly diffuse reflector will distribute normally incident light proportionate to the cosine of the observation angle measured from the surface normal. The actual performance of a surface is usually somewhere between the two extremes. Figures 14 and 15 show the bidirectional reflection distribution of smoked magnesium oxide, which, although not a coating to be used on SPS, is often a standard for reference to other coatings. The white paint which will probably be used on SPS structures is Z-93. Assuming that the binders of the two paints are the same, or at least produces similar surface properties, these figures can be scaled to represent the bidirectional reflectance of Z-93 paint. Its relative reflectance value is the ratio of the intensity measured at some angular location to the corresponding intensity which would result by perfectly diffuse total reflection of the incident flux. The general relationship is where R is the relative reflectance plotted in Figures 14 and 15, p-j is the reflectance value of smoked magnesium oxide, p2 is that of Z-93 paint, eM is the measurement angle, and is the incident angle. To illustrate the use of this relationship, one could find the reflected intensity from Z-93 paint at a measurement angle of 20° for green light (X = 0.5 p) incident at an angle of 30°. Figure 16 provides a "relative reflectance", R, of about .9 for smoked magnesium oxide. From Figure 16, it is seen that for green light (X = .5 micrometers) the reflectance, pp of smoked magnesium oxide is about .98. Figure 17 shows that the reflectance, p^, of Z-93 paint is about .9. It follows, then, that the anticipated reflected intensity is
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