What are the light source requirements for a spectrophotometer?

The requirements for a spectrophotometer light source include:

• Bright across a wide wavelength range
• Stable over time
• Long service life
• Low cost

Many light sources meet some of the requirements on this slide, but no light source can 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. Other instruments use a xenon lamp or xenon flash lamp suitable for the analysis target and aim of the analysis. A low- pressure mercury lamp that produces multiple emission spectra is effective for spectrophotometer wavelength calibration.