Apparatus for colorimetric analysis of a sample fluid, comprising: an optoelectronic device comprising: - a housing for said sample fluid; - a plurality of LED light sources that emit radiation of various wavelengths, ranging between 100 nm and 10 μm; - a driving unit for controlling said LED light sources ; - a bundle of optical fibres arranged in such a way as to receive as input the light radiation emitted by the LED light sources and transmit it to towards said housing ; and a measurement instrument for measuring light intensity and located downstream of the housing with respect to the path of the light radiation, characterised in that said optoelectronic device further comprises: - a light guide located upstream of said housing with respect to the path of the light radiation coming from the LED light sources , said bundle of optical fibres being interposed between the LED light sources and said light guide , said light guide mixing the various spectral components coming from the LED light sources and supplying a uniform beam as output towards said housing ; - a plurality of micro-lenses obtained on an inlet section of said light guide , each one of said micro-lenses receiving radiation from one of said optical fibres in the bundle. an optoelectronic device comprising: - a housing for said sample fluid; - a plurality of LED light sources that emit radiation of various wavelengths, ranging between 100 nm and 10 μm; - a driving unit for controlling said LED light sources ; - a bundle of optical fibres arranged in such a way as to receive as input the light radiation emitted by the LED light sources and transmit it to towards said housing ; and - a housing for said sample fluid; - a plurality of LED light sources that emit radiation of various wavelengths, ranging between 100 nm and 10 μm; - a driving unit for controlling said LED light sources ; - a bundle of optical fibres arranged in such a way as to receive as input the light radiation emitted by the LED light sources and transmit it to towards said housing ; and a measurement instrument for measuring light intensity and located downstream of the housing with respect to the path of the light radiation, characterised in that said optoelectronic device further comprises: - a light guide located upstream of said housing with respect to the path of the light radiation coming from the LED light sources , said bundle of optical fibres being interposed between the LED light sources and said light guide , said light guide mixing the various spectral components coming from the LED light sources and supplying a uniform beam as output towards said housing ; - a plurality of micro-lenses obtained on an inlet section of said light guide , each one of said micro-lenses receiving radiation from one of said optical fibres in the bundle. - a light guide located upstream of said housing with respect to the path of the light radiation coming from the LED light sources , said bundle of optical fibres being interposed between the LED light sources and said light guide , said light guide mixing the various spectral components coming from the LED light sources and supplying a uniform beam as output towards said housing ; - a plurality of micro-lenses obtained on an inlet section of said light guide , each one of said micro-lenses receiving radiation from one of said optical fibres in the bundle. <EOS>