and colour rendering for a particular lamp. In the operating
state, the mercury evaporates completely. The
other elements involved are present in saturated form
at the given temperatures, i.e. they only evaporate in
part; the rest is in liquid form at the coolest point in
the arc tube. The fraction of the filling that has evaporated
depends on the temperature of the coolest point
on the arc tube wall and also varies for the different
filling components. Changes to the temperature of the
arc tube wall can change the composition of the metal
halides in the discharge, thus also changing the colour
properties of the lamp.