Answer to Question #1046 Submitted to "Ask the Experts"

Q

I have heard a lot about UMF from PC monitors, but what about the cathode rays that aim straight into your face? Surely some of that gets through.

A

I have been asked to answer your question on CRT/VDT (computer monitor) and radiation. There is no danger from radiation from viewing a CRT. The dose to a person in the United States from working on a CRT for a year is less than a few mrem, which is about 1/10 of the dose from a chest x ray, or about the same amount you get in one day from natural radiation.

A CRT works by accelerating electrons, using a high-voltage source, and aiming them at the screen. The screen is made up of a material, called a phosphor, that emits light when struck by the electrons. (Electrons are the negative particles that orbit around all atoms.) One by-product of the electron interactions is x rays. The electrons (cathode rays) are completely stopped in the screen itself. The stopping is what produces low amounts of x rays, which is what accounts for the low level of radiation mentioned before. The CRTs operate at such a low level and produce less radiation than a modern television.

Prior to 1970, several studies were done to measure the radiation levels given off by televisions. Color televisions were known to produce some x rays. In the study, it was found that about 6% of them were above the recommended standard of 0.5 mrem hr^-1. Today's televisions use new screens and lower voltage, and so the amount of radiation (given off as x rays) is not detectable above background radiation unless you are using very sensitive x-ray counting equipment. For more information, see the Occupational Safety & Health Administration Web site discussion of computer workstations.

Bruce Busby, RSO