Iron core transformers use laminated silicon steel cores that have low losses at power frequencies such as 50 or 60 Hz. The high permeability of iron concentrates the magnetic flux, allowing efficient energy transfer with reasonable core size at low frequency. Ferrites and air cores are less efficient at these low frequencies for power levels typical of mains equipment. Laminations help reduce eddy currents, and core designs are optimized to balance no load losses, copper losses and cost for low frequency power applications.