medium pressure mersury lamps are the most common source of UV light used by the surface coating radiation curing industry.
As the name suggests, the lamp consists of mercury vapour at a pressure of between 102-105 torr enclosed in a glass envelope.
Two tungsten electrodes positioned at either and of the tube are used to pass an electric current through the lamp which excites the atoms of mercury.
These then emit radiation at various wavelengths as part of the process by which they return to thier ground state.
Although the most important emission is at 366nm, other emissions do occur and the pressure inside the glass envelope causes the lines to broaden quite considerably.
In fact a continuum is apparent from these types of lamps.
A typical spectral output from a mercury lamp is shown in Figure 21.