3.1. Radiation transmission/extinction parameters:

The major parameters which determine the optical performance of selective thin films are the spectral transmittance/absorbance (T and A), the transmission/absorption coefficient (т and tX), the skin depth (Of x), the refractive index (n) and the transmittance absorption product О Of), [3,61-67].

These parameters can be classified into two, namely, radiation transmission and radiation attenuation parameters. The radiation transmission parameters are those parameters which have to do with transmission of radiation. These are the transmittance and transmission coefficient.

On the other hand, the extinction coefficient, the refractive index, the absorption coefficient, the reflectance, and the skin depth, which have to do with radiation attenuation or extinction in materials are know as radiation attenuation parameters [3, 62, 63-67].

Of these optical parameters, the most important single parameter which gives an idea of the properties and behaviour of visible transparent window films is the spectral transmittance/absorbance curve in the 0.3 to1.0pm region. This is because both the radiation transmission and radiation attenuation parameters can be derived directly or indirectly from the spectral transmittance/absorbance curve of these films [65-66]. Also, the spectral transmittance/absorbance in the ultra violet-visible-near infrared (UV-VIS-NIR) region gives the behaviour and properties of transparent and semi-transparent selective thin films. Hence this investigation on the optical and spectral behaviour of some transparent and semi­transparent window films which were produced by the solution growth method is therefore carried out to determine the radiation transmission and radiation attenuation optical properties of the films. Also, the possible area of application of these films on the basis of these properties is suggested.