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External power frequency magnetic field-induced jitter on computer monitors
National Institute of Occuaptional Health, Umeå, Sweden.
National Institute of Occupational Health, Umeå, Sweden.
National Institute of Occuaptional Health, Umeå, Sweden.
National Institute of Occuaptional Health, Umeå, Sweden.
1993 (Engelska)Ingår i: Behaviour & Information Technology, ISSN 0144-929X, Vol. 12, nr 6, s. 359-363Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Power frequency magnetic fields with flux densities greater than 0.5 μT are not uncommon in offices. This level has been shown to induce jitter on VDT monitors. In the present project, these magnetic field-induced disturbances have been studied in the laboratory in order to establish a firm technical basis for future studies of the disturbance's influence on eye strain in VDT workers. Eight volunteers judged the occurrence of distortion when an applied external magnetic field was varied both in amplitude and frequency for 8 investigated VDT screens. The level of the external 50 Hz magnetic field when the distortion was detectable ranged from 0.6 to 1.1 μT. If the screen was viewed through a stereomicroscope (25 × magnification), the corresponding level was in the order of 0.2 μT. If the frequency difference between the external magnetic field and the refresh rate of the screen is only ±1-2 Hz, the disturbance is noticeable at even lower flux densities.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 1993. Vol. 12, nr 6, s. 359-363
Nyckelord [en]
jitter, magnetic field, VDT
Nationell ämneskategori
Arbetsmedicin och miljömedicin
Identifikatorer
URN: urn:nbn:se:umu:diva-99033DOI: 10.1080/01449299308924400ISI: A1993ML46900005OAI: oai:DiVA.org:umu-99033DiVA, id: diva2:785306
Projekt
digitalisering@umuTillgänglig från: 2015-02-02 Skapad: 2015-02-02 Senast uppdaterad: 2018-06-19Bibliografiskt granskad
Ingår i avhandling
1. Office work and physical factors: health aspects of electromagnetic fields and light
Öppna denna publikation i ny flik eller fönster >>Office work and physical factors: health aspects of electromagnetic fields and light
1997 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The overall aim of this thesis is to increase our knowledge of the physical environment of office workers with special focus on electromagnetic fields and to address the question of whether electromagnetic fields can directly or indirectly contribute to symptoms or discomfort among video display terminal ( VDT) workers. Furthermore, we have measured light modulation from various commonly used light sources in laboratory conditions and, as a second step, used modulated light as stimulus for provocation of neurophysiological responses in persons with perceived “electrical hypersensitivity” (EHS).During the last 20 years work-related illness among office workers has received increased attention. Changes in the physical environment, the introduction of VDTs and other electrical equipment and changes in light conditions have been discussed in this context. The basis for this thesis is the interdisciplinary Office Illness Project in Northern Sweden. Using a questionnaire completed by 4,943 office workers, 150 VDT workers with or without facial skin symptoms were selected for a case referent study of the electromagnetic fields in offices.When the measurements in the offices were performed in 1989, the general level of the 50 Hz magnetic fields in the offices was rather low, but in 5% of the offices the flux density exceeded 0.5 pT. At this level VDT monitors were shown to display detectable instability (jitter). Furthermore, the ability of test subjects (healthy volunteers) to detect jitter was shown to depend on both the amplitude and frequency characteristics of this instability. The study indicates that the instability of computer monitors and thereby the instability of the visual image of the VDT screen might be an increasing problem since it is known that the harmonic content of the general magnetic field in offices is on the rise.VDT monitors contributed to the magnetic field level at VDT workplaces in both extremely low and very low frequency ranges. However, the dominant source of electric fields in rooms was ungrounded electrical equipment, not VDT screens.High electric fields in the extremely low frequency range in the offices were associated with skin symptoms among VDT workers. The causal nature of this association cannot be determined since it may depend on undetected factors related to exposure. No associations were found, however, for any of the VDT-related electromagnetic fields and skin symptoms.Commonly used fluorescent tubes in our office environment have a degree of modulation of the light (flicker) that varies widely from less than 1% (fluorescent tubes with high frequency gear) up to nearly 100%. When persons with perceived EHS were exposed to flickering light, a higher amplitude of brain cortex responses were found at all tested frequencies compared with control subjects. These findings are of considerable interest, but further studies are required in order to establish a possible relationship between flickering light and discomfort/symptoms in persons with perceived EHS.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå universitet och Arbetslivsinstitutet, 1997. s. 46
Serie
Umeå University medical dissertations, ISSN 0346-6612 ; 530
Nyckelord
Facial skin symptoms, office illness, electrical hypersensitivity, physical environment, flicker, jitter, neurophysiological effects
Nationell ämneskategori
Arbetsmedicin och miljömedicin
Identifikatorer
urn:nbn:se:umu:diva-96906 (URN)91-7191-386-6 (ISBN)
Disputation
1997-11-28, Stora föreläsningssalen, Arbetslivsinstitutet, Umeå, Umeå universitet, Umeå, 09:30
Handledare
Projekt
digitalisering@umu
Tillgänglig från: 2015-02-02 Skapad: 2014-12-05 Senast uppdaterad: 2018-06-07Bibliografiskt granskad

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Sandström, MonicaHansson Mild, KjellSandström, Mattias
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