Abbrev. for very low-frequency magnetic field. CRT displays, transformers, fluorescent lights, etc., can emit magnetic fields at low frequency (50 Hz to 100 kHz) that some allege can be harmful to humans. There is currently no consensus as to the levels or exposure limits that might be harmful. Concerns about the harmful effects of VLFMFs is also encountered with respect to power transmission lines and are highly contentious. These effects are claimed or denied by their respective pressure groups.