Sources of ELF:

One ELF source which has received much publicity is the general cathode-ray tube (CRT) monitor of the kind used in desktop personal computers. (Really, CRT monitors generate EM energy at higher frequencies, not only at ELF.) The other parts of a computer are not responsible for much EM energy. The notebook and Laptop computers generate necessarily none.

In the CRT, the characters & images are formed as electron beams strike a phosphor coating on within of the glass. The electrons change direction continuously as they sweep from left to right and from top to bottom on the screen. The sweeping is caused by deflecting coils which steer the beam across the screen. The coils produce magnetic fields which interact with the negatively charged electrons, forcing them to change the direction. The fields therefore fluctuate at low frequencies. Since of the locations of the coils and the shapes of the fields enclosed them, there is more EM energy "radiated" from the sides of a CRT monitor cabinet than from the front. When there is any health hazard with ELF, and hence it is greatest for someone sitting off to the side of a monitor and least for somebody seeing the screen from directly in front.