Thermal equilibrium in gas-discharge plasma of low pressure mercury lamp

A study was conducted emission spectra germicidal low pressure mercury lamp at currents 100–306 mA located in a closed opaque cavity. It is shown that the lamps located in the cavity with perfectly reflecting and absorbing internal surfaces, in the emission resonance line of mercury is dominant at λ r = 253.65 nm. The same pattern is observed in the tube placed in a cavity with diffusely reflecting surface at a low current of about 100 mA. However the picture of spectrum changes at higher discharge current. The spectrum of the lamp with arc discharge at a current of 306 mA contains the maxima of the spectral lines. Its intensities are approximately described by Planck's radiation law at the temperature of 9270 ± 230 K. The mechanisms of establish thermal equilibrium are discussed.