How do mercury-vapour lamps produce bluish light rich in ultraviolet radiation?

Mercury-vapour lamps produce light through an electric discharge process where an applied voltage creates an electric field within a container, such as a quartz tube, that holds mercury vapour and a noble gas.21

This electric field excites the mercury atoms, raising their outermost electrons to higher energy levels. As these electrons return to their ground state, they release energy in the form of [electromagnetic radiation].23

The specific characteristics of the light depend on the pressure of the mercury vapour:

• Ultraviolet Radiation: At low pressures, mercury atoms primarily emit intense ultraviolet radiation, particularly at a wavelength of 254 nanometres.3
• Bluish Visible Light: At high pressures, the collision frequency between mercury atoms increases significantly. This causes the spectral lines to broaden, distributing radiation across various wavelengths. The emissions between 405 and 546 nanometres manifest as visible light with a characteristic bluish-green colour.31

Because these lamps emit significant ultraviolet radiation, they are often housed in materials like quartz that transmit this radiation more effectively than ordinary glass.2