COMMON SOURCES

One ELF source that has received much publicity is the common cathode-ray tube (CRT) monitor of the sort used in desktop personal computers. (Actually, CRT monitors produce EM energy at higher frequencies, not only at ELF.) Other parts of a computer are not responsible for much EM energy. Laptop and notebook computers produce essentially none. In the CRT, the characters and images are created as electron beams strike a phosphor coating on the inside of the glass. The electrons change direction constantly as they sweep from left to right and from top to bottom on the screen. The sweeping is caused by deflecting coils that steer the beam across the screen. The coils generate magnetic fields that interact with the negatively charged electrons, forcing them to change direction. The fields thus fluctuate at low frequencies. Because of the positions of the coils and the shapes of the fields surrounding them, there is more EM energy “radiated” from the sides of a CRT monitor cabinet than from the front. If there’s any health hazard with ELF, therefore, it is greatest for someone sitting off to the side of a monitor and least for someone watching the screen from directly in front.