In 1991, I was working as a technical manager on an electrical engineering task force. There were about 20 of us on the electrical design team and each of us had a computer and CRT on our desk. Most of us, including I, used the computers to run Computer Aided Design (CAD) software and, with this particular software, there were two separate modes. Text and Graphic.
Whenever I switched my computer from 'text' to 'graphics', the CRT screen reeled, for perhaps one second, with a series of waved lines and color patterns. I noticed that, during that brief transition, I felt very uneasy; a kind of uneven nausea-like feeling in my upper chest.
I wasn't convinced. After all, if you're suddenly watching screen images that ripple like a flag in the wind, it would be logical to conclude that the physical sensation is only the result of the associated visual experience. So from that point forward, I always closed my eyes before I switched to the graphics mode. But, the physical sensation continued, even with no visual cue.
Well, this was no scientific test. With my eyes closed, I still knew that I was switching to graphics; therefore, the entire experience was still subjective and possibly imaginary.
Then, one day, one of our purchasing agents entered the area with a gift that he'd received from a salesman. It was a current detector in the form of a small flashlight. The kind that lights when it's placed near an active electrical circuit. I immediately grabbed the device, ran to my computer, and made the switch from text to graphics; while holding the device about 4 inches away from the CRT screen. The detector remained perfectly dark until the transition began. Then, it lit up like a flash bulb.
This is clearly not proof that the electromagnetic field was impairing my health. But it does prove that the sick feeling I had was not imaginary; that it was caused by a sudden change in the field.
If the EMF of a 20KV electrical source (like the flyback transformer in a CRT monitor) 150 feet away is 0.28 milligauss, then the EMF at 300 feet will only be 0.28 / 2 squared = 0.28 / 4 = 0.07 milligauss.
Conversely, at 75 feet, it will be 0.28 x 4 (1.12), at 37.5 feet 1.12 x 4 (4.48), at 18.75 feet 4.48 x 4 (17.92), at 9.375 feet 17.94 x 4 (71.68), and at the 4.7 feet between your CRT and you 71.76 x 4 (287 milligauss). Compared to the concern over school children within 150 feet of power transmission lines (3.2 milligauss), the influence of a computer (or television) CRT's electromagnetic field is (287 / 3.2) or about 90 times stronger.
In contrast, an LCD television or computer monitor utilizes a "clipped" D.C. power supply. The electromagnetic field does oscillate, but at a peak intensity of less than 1/1000th of a CRT's. At today's prices and quality, why not buy an LCD?