UV-visible spectrophotometers have two light sources: one for the UV, and one for the visible regions of the EMR spectrum. The most common UV sources is a high-pressure deuterium lamp. For the visible region, the traditional source is a simple tungsten filament bulb; however improved performance can be obtained using a more modern quartz halogen bulb. An instrument will typically have a simple mirror mechanism that switches between the two at a specific wavelength, and may also include a feature to turn the deuterium lamp off completely when it is not going to be used.

[Need images of the three types of bulbs, with some text explanation]

Parts of a UV-Vis spectrophotometer: Light Sources | Wavelength Selector | Sample Compartment | Detector