  Disordered media coatings are finding increasing use in applications such as
day-time radiative cooling paints and solar thermal absorber plate coatings
which require tailored optical properties over a broad spectrum ranging from
visible to far-IR wavelengths. Both monodisperse and polydisperse
configurations with thickness of coatings up to 500 micrometer are currently
being explored for use in these applications. In such cases it becomes
increasingly important to explore utility of analytical and semi-analytical
methods for design of such coatings to help reduce the computational cost and
time for design. While well-known analytical methods such as Kubelka-Munk and
four-flux theory have previously been used for analysis of disordered coatings,
analysis of their utility has so far in literature been restricted to either
solar spectrum or IR but not simultaneously over the combined spectrum as
required for the above applications. In this work, we have analysed the
applicability of these two analytical methods for such coatings over the entire
wavelength range from visible to IR, and based on observed deviation from exact
numerical simulation we propose a semi-analytical technique to aid in the
design of these coatings with significant computational cost savings.
