By measuring the power balance for high current AC and DC vortex stabilised arcs it has been shown that the radiative efficiencies of AC and DC arcs are comparable to each other at similar power input levels. The electrode power balance has also been determined as a function of the significant arc parameters (current I, gas pressure, flow direction and rate). Further details on electrode heat transport were obtained by measuring the spatial and temporal variations of electrode surface temperature using a two-wavelength pyrometric technique. The heat transfer to the walls and exhaust gas depend linearly on the radiation losses. The former loss is larger than expected from laminar heat flow models indicating that heat losses are enhanced by turbulence in the gas flow. The power balance data confirm that the AC vortex stabilised arc lamp is comparable to the DC arc and has the added prospect of lower electrode erosion because of the smaller average electrode heat fluxes in the AC arc.