Dear Mostapha
thanks for your reply but i could not implement it well, and i wish that the below information will be sufficient to help, bcz this is really important to me and otheres who deals with Horticulture and Landscape in same time.
The most common plastic materials used as agricultural films are the low density polyethylene (LDPE, with a density less than 0.93 kg m−3), the copolymer of ethylene and vinyl-acetate (EVA)
Also here you can find the characteristics of the flexible materials for greenhouse covers (adapted from CPA, 1992 and Tesi, 2001) as much as i get.
UV-PE Film ( UV-PE~ polyethylene Long life or UV)
Thickness (mm) = 0.18
Direct PAR transmissivity (%) = 90
Diffuse PAR transmissivity (%)= 86
Long-wave IR transmissivity (%)= 65
EVA Film ( EVA~Ethylene vinyl-acetate copolymer)
Thickness (mm) = 0.18
Direct PAR transmissivity (%) = 90
Diffuse PAR transmissivity (%)= 76
Long-wave IR transmissivity (%)= 27
and here you will find the global heat transfer coefficient’ (K in W m−2 °C−1) for the above greenhouse covering materials, measured under normalized conditions (temperatures: exterior: −10°C, interior: +20°C, wind: 4 m s−1). (Source: Nisen and Deltour, 1986.)
Cover Clear sky Overcast Sky
Single PE 8.8-9.0 7.1- 7.2
Single EVA 7.8 6.6
Note : the PAR radiation (photosynthetically active or photoactive radiation and its the amounts to 45–50% of the global radiation; Berninger, 1989)
The name PAR is used to designate the radiation with wavelengths useful for plant photosynthesis. It is accepted that the PAR radiation ranges from 400 to 700 nm (McCree, 1972), although some authors consider the PAR from 350 to 850 nm.
The composition of the radiation changes with time, as a function of the Sun’s elevation and the cloudiness. When the Sun is low over the horizon, the short wavelengths are reduced (less UV and more red). The clouds reduce the amount of energy, greatly decreasing the NIR.
The PAR proportion in relation to the global radiation increases with scattering (diffusion). It is lower with clear sky and in the summer (45–48%).
kind regards
rafat