A mercury-vapor lamp excites Mercury atoms in an electrical discharge and collects the light emitted as they relax. Its output contains characteristic spectral lines; the lamp's pressure and construction affect their widths and the balance between lines and background.
A spectroscope separates those lines, making the lamp useful for wavelength references and optical excitation. Some emitted ultraviolet radiation can excite a phosphor, which converts it into a broader visible output. The observed spectrum then depends on the discharge, envelope transmission and any conversion coating; it is not simply the isolated-atom spectrum at every operating condition.
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A gas-discharge lamp is a type of electric light source that produces light by passing an electric current through a gas or vapor, causing it to emit light. These lamps work on the principle of gas ionization, where the gas molecules are excited by the electric current, resulting in the release of energy in the form of visible light.
