What is “lamp switching” in a spectrophotometer?

As stated above, halogen lamps and deuterium lamps are used in many spectrophotometers.

The graph at left shows their respective energy distributions measured by a UV-1800 UV-VIS Spectrophotometer. The light sources are switched near 300 nm to 350 nm, where the emission intensities of the halogen lamp and deuterium lamp are approximately equal. The light sources can be switched by moving the lamps themselves or by rotating a reflector.

The figure at right shows the switching method by rotating a reflector. By changing the tilt of the reflector positioned between the halogen lamp and the deuterium lamps, the light beam that enters the monochromator can be switched. In most instruments, the optimal tilt with respect to each light source is automatically adjusted during the initial setup operation after the power is turned on, which eliminates the need for positional adjustment by replacing lamps.