Investigation of the Spectral Optical Properties of the Liquid Radiation Filters for Using in the Greenhouse Applications

In this article a mathematical method is established for predicting the monochromatic radiative properties(optical constants)of liquid radiation filters. The liquid radiation filter, LRF, is used as a selective solar radiation absorber for controlling the greenhouse temperature in a hot climate. LRF strongly absorbs the UV (ultraviolet) and NIR(near infrared) wave bands and highly transmits the PAR (photosynthetically active radiation) wave band. Moreover it is used as physical plant growth regulator in photomorphogenesis studies. The monochromatic optical constants of the LRF such as the refractive index n_f,λ, the absorption coefficient of σ_f,λ and the dimensionless extinction coefficient k_f,λ are mathematically investigated by using the ray tracking technique. The transmittance due to absorption of the LRF τ_f,λ was investigated by considering the reflectance on the fluid surface. The consideration of a simplified refractive index n_f,λ instead of a refractive index with complex part (n_f,λ-ik_f,λ) for the LRF is also examined because the LRF is highly absorptive radiatively and highly conductive electrically. The results of the present study show that all the monochromatic optical constants of the LRF can be investigated mathematically by using some limiting measured values of the spectral transmittance and reflectance. The simple refractive index n_f,λ can be used for the LRF instead of the one with a complex part.