An instrument which combines a spectrograph with a photometer. In a conventional photometer the wavelengths measured are selected with a filter; in a spectrophotometer, the filter is replaced by a spectrograph to split up the light according to wavelength. A spectrophotometer has the advantage when the wavelength range of interest is 3 nm or less because it is difficult to make filters of such narrow bandwidth. Any modern spectrograph with a charge-coupled device or similar detector is indistinguishable from a spectrophotometer.