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This thesis describes a new investigation into the relationship between the developed colour intensity of photochromic textiles and the time of UV exposure and also the time of relaxation. As a result of this relationship the potential of flexible textilebased sensor constructions which might be used for the identification of radiation intensity is demonstrated. In addition the differences between photochromic pigment behaviour in solution and incorporated into prints on textiles are demonstrated. Differences in the effect of the spectral power distributions of light sources on the photochromic response are also examined. Bi-exponential functions, which are used in optical yield (Oy) calculations, have been described to provide a good description of the kinetics of colour change intensity of photochromic pigments, giving a good fit. The optical yield of the photochromic reaction Oy is linearly related to the intensity of illumination E. The optical yield obtained from the photochromic reaction curves are described by a kinetic model, which defines the rate of colour change initiated by external stimulus of UV light. Verification of the kinetic model is demonstrated for textile sensors with photochromic pigments applied by textile printing and by fibre mass dyeing. The thesis also describes a unique instrument developed by author, which measures colour differences ΔE* and spectral remission curves derived from photochromic colour change simultaneously with UV irradiation. In this theses the photochromic behaviour of selected pigments in three different applications (type of media – textile prints, non-woven textiles and solution is investigated.