For Waters HPLC systems, the lamps used depend mainly on the detector type (UV, PDA, fluorescence, etc.). In most common cases (UV/UV-Vis detectors), the lamp is a deuterium (D₂) lamp.
Deuterium (D₂) Lamp — most important
Used in UV / UV-Vis detectors (e.g., Waters 2487, 2489, PDA detectors)