Properties of the positive column of low pressure Hg/Ar discharge have been investigated from the point of view of its application in fluorescent lamps. The results obtained are based on experimental methods to determine both UV redonance radiation fluxes of the 63P, and 6IPI Hg levels and t o measure the electron distribution function by probes; in addition a kinetic model is applied for the theoretical interpretation of the experimental results and to give a deeper insight into the particle and energy budget. I n the present first part of the paper the effects of recently determined Teff-values on radiation, net collision rates, power transfer nnd the electron energy distribution for extended parameter values are investigated especially in dependence on mercury partial pressure.