Visible solar transmittance

Figures 7.5 and 7.6 give the measured spectral reflectances and transmittances of fabrics. It is clear from Figure 7.5 that color (6,white 7,black 1,yellow) has a significant effect in reflecting solar irradiance, and also we see why these colors can be discriminated in the visible spectral region of 0.6 pm. However, in the spectral range relevant to fire conditions, color has less of an effect. Also, the reflectance of dirty (5a) or wet (5b) fabrics drop to <0.1. Hence, for practical purposes in fire analyses, where no other information is available, it is reasonable to take the reflectance to be zero, or the absorptivity as equal to 1. This is allowable since only thin fabrics (Figure 7.6) show transmittance levels of 0.2 or less and decrease to near zero after 2 pm.

CD Cu-S(e) films have been proposed for a number of different potential applications. Solar control coatings, where the visible and IR transmission and reflectivity can be varied, is probably the most studied, e.g.. Refs. 44 and 45. The relatively high conductivity and the partial transmittance in the visible spectrum are useful for transparent conductors [46]. Other possible applications are for Cu sensor electrodes and electrical contacts for ceramic devices [46]. 

In a similar manner, Cn3SbS4 was formed by depositing a layer of CuS (as earlier) onto a previonsly deposited film of SbiSs (from a thiosnlpahte bath) and annealing in N2 at 250°C [33], These films (typically between 0.1 and 0.3 p.m thick) were highly condncting (some tens of O/sq). The films were evaluated for solar-control pnrposes and exhibited good IR reflectivity/low IR transmittance with snfficient visible transmittance. 

Fig. 7. Transmittance (and reflectance) of a spectral splitter mirror as a function of solar wavelength in microns. This response depicts that of a "hot mirror in which light is transmitted in the visible region and reflected in the infrared.

Polycrystalline ZnO for window layers in solar cells are most frequently prepared by magnetron sputtering. Optimized layers have resistivities of 1.5-2x10 " Ocm with Hall mobilities of up to 60 cmWs, refractive indices of approximately 2.0 and an average transmittance of 85 % in the visible range. The best values of the mobility in optimized films have reached the... 

In space the solar energy maximum emission from the sun occurs at approximately 550 nm (2). Thus for some space applications, polymers are required that have a high transmittance at 550 nm, so there is a need for polyimides more transparent than Kapton throughout the visible region. 

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