The principle of the standard diode array: The tungsten lamp emits light in the visible range and enters the deuterium lamp, which adds UV (and visible) light. The polychromatic beam passes the flow cell, the grating splits up the polychromatic beam to different wavelengths, the intensities of which are measured by an array or photodiodes. The main difference between the DAD and the VWD is that all available wavelengths are measured simultaneously, i.e. that spectra can be acquired and multiple single wavelengths at the same time by different diodes in the array. As substances can be identified by their spectra, the DAD has a high selectivity.