What types of radiation do VDTs emit?
Most VDTs currently in use are based on cathode-ray tube (CRT) technology and the information in this bulletin applies only to this type of VDT. The VDT is designed to emit visible radiation (light) with a brightness that is adjustable by the operator. In creating the display, however, other types of electromagnetic radiation are also generated, in particular, extremely low frequency, radiofrequency, infrared, ultraviolet and X-ray radiation. The CRT is an evacuated glass tube which has a source of electrons at one end and a screen, which is coated on the inside with a phosphor, at the other. When a sufficiently high voltage is applied to the CRT, a focussed beam of electrons is produced which is then scanned across the screen. The beam is switched on and off in order to generate the display. The interaction of these electrons with the phosphor causes the emission of visible radiation, plus a small amount of ultraviolet radiation, from the screen. This interaction also produces low ene
