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.