A fluid analysis system configured to operate downhole in a well traversing a formation, the fluid analysis system comprising: at least one light source (130, 180, 250) generating an input light; a sample cell (184, 256) operably connected to said at least one light source (130, 180, 250) receiving a sample fluid therein, said sample cell (184, 256) comprising: at least one input window (136, 240) allowing said input light to flow into said sample cell (184, 256) and through the sample fluid to produce an output light; and at least one output window (136, 240) allowing said output light to flow out of said sample cell (184, 256); at least one first spectrometer (186, 260) operably connected to the output of said sample cell (184, 256) and being configured to measure said output light and generate a plurality of measurement signals; and an analysis device operably connected to outputs of said at least one first spectrometer (186, 260) and being configured to receive said plurality of measurement signals and determine properties of the sample fluid; characterized in that fluid analysis system further comprises: at least one second spectrometer (187, 254) operably connected to receive light directly from said at least one light source (130, 180, 250) and configured to measure said input light and generate a plurality of reference signals; and a calibration device operably connected to outputs of said at least one second spectrometer (187, 254) and configured to receive said plurality of reference signals and calibrate said at least one first spectrometer (186, 260) and other electronics, wherein said first spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer and said second spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer. at least one light source (130, 180, 250) generating an input light; a sample cell (184, 256) operably connected to said at least one light source (130, 180, 250) receiving a sample fluid therein, said sample cell (184, 256) comprising: at least one input window (136, 240) allowing said input light to flow into said sample cell (184, 256) and through the sample fluid to produce an output light; and at least one output window (136, 240) allowing said output light to flow out of said sample cell (184, 256); at least one input window (136, 240) allowing said input light to flow into said sample cell (184, 256) and through the sample fluid to produce an output light; and at least one output window (136, 240) allowing said output light to flow out of said sample cell (184, 256); at least one first spectrometer (186, 260) operably connected to the output of said sample cell (184, 256) and being configured to measure said output light and generate a plurality of measurement signals; and an analysis device operably connected to outputs of said at least one first spectrometer (186, 260) and being configured to receive said plurality of measurement signals and determine properties of the sample fluid; characterized in that fluid analysis system further comprises: at least one second spectrometer (187, 254) operably connected to receive light directly from said at least one light source (130, 180, 250) and configured to measure said input light and generate a plurality of reference signals; and a calibration device operably connected to outputs of said at least one second spectrometer (187, 254) and configured to receive said plurality of reference signals and calibrate said at least one first spectrometer (186, 260) and other electronics, wherein said first spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer and said second spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer. at least one second spectrometer (187, 254) operably connected to receive light directly from said at least one light source (130, 180, 250) and configured to measure said input light and generate a plurality of reference signals; and a calibration device operably connected to outputs of said at least one second spectrometer (187, 254) and configured to receive said plurality of reference signals and calibrate said at least one first spectrometer (186, 260) and other electronics, wherein said first spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer and said second spectrometer comprises at least one filter array spectrometer and at least one grating spectrometer.