This thesis describes the design and construction of two instruments for use in isolating the ultraviolet parts of the Solar spectral irradiance at Earth's surface. The first was a total UVA Pyranometer, which was undertaken to make preliminary investigations in the techniques of monitoring ultraviolet irradiances, as well as to provide useful data. The main part of this thesis was the construction of a portable, easily operated, interference filter spectrophotometer to isolate the ultraviolet-B spectrum into five discrete 10 nm passbands. However, as further reading will describe, realisation of only the two longer wavelength passbands was made due to deviations from the ideal quasi-rectangular passbands of the interference filter spectral transmittance curves. Discussion of how these problems can be overcome is presented in the conclusion. An outline on how the incident spectral solar irradiance could be found, from the five passbands, is presented along with some preliminary data from the two operational channels. An overall accuracy of 15% was obtained for data obtained, with better accuracies, to 7%, attainable by stabilisation of the instrument power supplies and, therefore, output voltage.