| 1. |
- Andersson, N., et al.
(författare)
-
Amplitude modulation of light from various sources
- 1994
-
Ingår i: Lighting Research and Technology. - : Sage Publications. - 1477-1535 .- 1477-0938. ; 26:3, s. 157-160
-
Tidskriftsartikel (refereegranskat)abstract
- This work was done to obtain basic knowledge about various light sources and specially about light modulation, or flicker. The study showed that the modulation of light varied a lot between different ordinary light sources. In general the 100 Hz component in the flickering light dominated. For incandescent lights the modulation increased with decreasing power and was in the range 10-22%. Light from the tungsten-halogen lamps had 2-6% modulation. The most common light sources (single-colour fluorescent light) had a modulation of about 20%. Fluorescent tubes with better colour rendering (full-colour fluorescent and full-colour special fluorescent tubes) had a higher modulation, 30-40%, while light from high-frequency (HF) fluorescent tubes had a modulation of 0.9%. Light from conventional compact fluorescent tubes had a modulation degree of about 44%, and for HF compact fluorescent tubes it was 2-7%. Modulation of light from HF compact fluorescent tubes had a tendency to decrease with increasing tube size. The modulation of light from discharge lamps was in the range of 52% up to 100% and the curve form of the light from low pressure sodium vapour lamp (100% modulation) contained several high frequency components.
|
|
| 2. |
- Sandström, Monica, 1946-, et al.
(författare)
-
External power frequency magnetic field-induced jitter on computer monitors
- 1993
-
Ingår i: Behaviour & Information Technology. - : Taylor & Francis. - 0144-929X .- 1362-3001. ; 12:6, s. 359-363
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Sandström, Monica, 1946-, et al.
(författare)
-
Neurophysiological effects of flickering light in patients with perceived electrical hypersensitivity
- 1997
-
Ingår i: Journal of Occupational and Environmental Medicine. - : Wolters Kluwer. - 1076-2752 .- 1536-5948. ; 39:1, s. 15-22
-
Tidskriftsartikel (refereegranskat)abstract
- An increasing number of people in Sweden are claiming that they are hypersensitive to electricity, These patients suffer from shin as well as neurological symptoms when they are near computer monitors, fluorescent tubes, or other electrical appliances, Provocation studies with electromagnetic fields emitted from these appliances have, with only one exception, all been negative, indicating that there are other factors in the office environment that can effect the autonomic and/or central nervous system resulting in the symptoms reported, Flickering light is one such factor and was therefore chosen as the exposure parameter in this study, Ten patients complaining of electrical hypersensitivity and the same number of healthy voluntary control subjects were exposed to amplitude-modulated light, The sensitivity of the brain to this type of visual stimulation was tested by means of objective electrophysiological methods such as electroretinography and visual evoked potential, A higher amplitude of brain cortical responses at all frequencies of stimulation was found when comparing patients with the control subjects, whereas no differences in retinal responses were revealed.
|
|
