Measurements of extremely low-frequency magnetic fields around video display terminals

The extremely low-frequency (ELF) magnetic field emissions of seven video display terminal (VDT) models were measured. A measuring coil with a linearized frequency response (50 Hz to 25 kHz) was used. The dominating ELF magnetic field around the terminals was the 50 or 60 Hz asymmetric triangular waveform from the vertical deflection coil of the cathode ray tube. At the distance of 50 cm, the magnetic field strength was still slightly higher than the background level in usual office rooms, but several orders of magnitude lower than the thresholds of known interaction mechanisms. Some recent experiments suggest that certain biological effects may occur at field strengths only a few times higher than those found at the position of VDT operators, but the significance of these effects to human health is not known.