What colors of light are produced by sodium-vapour lamps and mercury-vapour lamps?

The colors produced by these lamps depend on the pressure at which the vapor is excited:

• Sodium-vapour lamps: Low-pressure sodium (LPS) lamps emit a nearly monochromatic yellow light. High-pressure sodium (HPS) lamps, which contain a mixture of mercury and sodium, produce a whiter light.1
• Mercury-vapour lamps: At high pressures, mercury-vapour lamps emit a bluish-green light. By using phosphors to transform a portion of this emission, these lamps can also be used to produce white light. Generally, mercury vapour is associated with blue or bluish light.234

It is important to note that the specific spectral output and perceived color can be influenced by the lamp's internal pressure and the presence of other gases or coatings.123