The properties of polycrystalline silicon films have been investigated in relation to low pressure chemically vapour deposited (LPCVD) conditions, such as gas chemical content, pressure and temperature in the range of 500-615 degreesC. A careful investigation of the 250-400-nm reflection spectra indicates a definite dependence on the temperature and growth rate for LPCVD poly-Si films. The disorder in as-deposited samples produces changes to the main peaks of optical transition in c-Si described by the complex band theory. The percentage of the disorder has been associated with changes in Gamma'(23)-Gamma (15) at 365-nm and in X-4-X-1 at 280-nm optical transitions obtained by a deconvolution approach to UV spectra. The most disordered LPCVD poly-Si samples have been obtained at 550 degreesC for a deposition pressure of 400 mtorr. Optical properties are discussed in relation to CVD conditions and are related to XRD data.