**7. Radiation fluxes formulae**

As part of measurements, formulas for generating the different radiation fluxes: global (total) solar irradiance, H and its components, direct solar irradiance Hb, diffuse solar irradiance Hd, are developed to generate the required data of these radiation fluxes where they are required and are not regularly measured. Some of the expressions were developed in terms of other easily measured radiation and meteorological parameters. Numerous of these formulae exist, developed by many workers and published in relevant journals all over the world.

However many of them may not be applicable globally or valid at other geographical locations different from where they were generated(Page, 1964, Schulze,1976), while some of them may be applicable at geographical locations similar in latitude to where they were originated (Chuah et.al, 1981). Some of them are the Angstrom type (Angstrom,1924; Rietveld, 1978). Some are linear (Shears et.al, 1981 ; Glover and McCullouch 1958). Some are polynomials, some are parametric while some are indicial.
