Question

The light source is a combination of deuterium lamp and tungsten lamp. Why two lamps are necessary?

Answer 1

Answer:

Many light sources meet some of the requirements above but no light source is able to meet them all. Many spectrophotometers switch between a halogen lamp for the visible range and a deuterium lamp for the ultraviolet range according to the wavelength setting.

This is because of the difficulty in achieving both "a high degree of brightness" and a "uniform brightness distribution" across a wide wavelength range using a single light source. Switching between light sources with different emission wavelength ranges also offers the advantages of reducing the excess incident light into the monochromator and reducing the amount of stray light (Reference