STENGEL@pucc.Princeton.EDU (Robert F. Stengel) (02/12/91)
Inadvertently, I conducted an experiment relating to the on-going controversy regarding possible health effects of low-level electric fields and video data terminals (VDT). My new Macintosh LC computer is parked unceremoniously in the middle of my desk until I can find a better place for it. The dual-15w-tube fluorescent desk lamp that has served me well for 30+ years sits overhead, usually well out of the way. The lamp has separate "on" and "off" buttons; the "on" button must be held down to produce a higher electric field during the starting cycle. Recently, while sorting some 35mm slides, I pulled the lamp head closer to the desk top, just a few inches above the monitor screen. When I turned the computer on, the lamp tube nearest to the monitor began to fluoresce, flickering until the "off" button produced total discharge. Apparently, the electric pulse that occurred when the monitor was turned on was enough to initiate fluorescence in the lamp. The phenomenon has been repeated several times since. In the popular reporting on the subject, much has been made of average field strengths and possible repercussions on health, but little or no attention has been paid to peak transient fields, which could be expected to have increased effect. It may well be that the VDT presents a greater hazard as it is being turned on than while it is operating normally. Increased understanding of this potentially significant factor is warranted.
jmc@DEC-Lite.Stanford.EDU (John McCarthy) (02/12/91)
Possibly the interaction between the VDT and the fluorescent lamp was via the power line.
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (02/12/91)
In article <12438@pucc.Princeton.EDU> STENGEL@pucc.Princeton.EDU writes: > Recently, while sorting some 35mm slides, I pulled the lamp head closer >to the desk top, just a few inches above the monitor screen. When I turned >the computer on, the lamp tube nearest to the monitor began to fluoresce, >flickering until the "off" button produced total discharge. Apparently, the >electric pulse that occurred when the monitor was turned on was enough to >initiate fluorescence in the lamp. The phenomenon has been repeated >several times since. First of all, since the pulse only occurs for a short period of time, the exposure (which is cumulative anyway) is quite slight. Secondly, the exposure from VDTs may be one of the less important elements in the environment. I have shared offices with 250 KW transmitters where fluorescent lights would burn a bright white while unplugged and held in the hand, and caused small sparks to jump off the corner of my glasses if the sharp edges were not rounded with a file. Currently I am across the street from a radar set which causes a noticeable flicker on fluorescent lamps and disconnected CRTs every time the beam sweeps in my direction. VDT exposure is in the sub-microvolt/m2 range, but there are a lot of environments where people live and work in the tens of volts/m2 range. AC power lines are a contributor to the exposure, and while the actual field strength produced by AC lines is quite small in most cases, the lower frequencies may possibly be more hazardous. Personally, I wouldn't worry about it. But it's a matter that certainly does deserve more study. --scott
jones@sj.ate.slb.com (Clark Jones) (02/13/91)
In article <12438@pucc.Princeton.EDU> STENGEL@pucc.Princeton.EDU writes: [stuff deleted] > In the popular reporting on the subject, much has been made of average >field strengths and possible repercussions on health, but little or no >attention has been paid to peak transient fields, which could be expected to >have increased effect. It may well be that the VDT presents a greater >hazard as it is being turned on than while it is operating normally. >Increased understanding of this potentially significant factor is warranted. And the designers of this equipment, in their infinite wisDUMB, put the on/off switches on the _BACK_ so you've got to get "up close and personal" to turn the thing on or off! BTW, you didn't mention whether the VDT in question is a monochrome or color. For many years, standard design of color CRT circuits has included a "de-gausser", which applies a decaying line-frequency magnetic field to the tube to eliminate residual magnetic fields (which would interfere with the image displayed). This is applied to the face end of the tube. Clark Disclaimer: The opinions expressed above are mine and not those of Schlumberger because they are NOT covered by the patent agreement!