A closed 13.6 MHz inductively coupled argon plasma with a volume of 2 cm3 is investigated by active and passive diagnostics. The study considers the influence of varying argon filling pressures in the range 10 - 100 mbar and different input powers in the range 50 - 125 W. The combination of the applied techniques of absolute line emission intensities, Thomson scattering and diode laser absorption measurements reveals the typical behaviour of temperature and electron density of the plasma. One of the observed characteristics is that, upon increasing the filling pressure, the ring-shaped radial distribution of the electron density becomes more pronounced, while the electron temperature decreases over the whole radial profile. Furthermore, the influence of input power on the electron temperature and density depends strongly on the filling pressure. It is to be expected that insight into plasma processes and parameters for argon filling will lead to a better understanding of future light sources as well.