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- Andersson, N., et al.
(författare)
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Amplitude modulation of light from various sources
- 1994
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Ingår i: Lighting Research and Technology. - : Sage Publications. - 1477-1535 .- 1477-0938. ; 26:3, s. 157-160
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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.
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| 2. |
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| 3. |
- Sandström, Monica, 1946-, et al.
(författare)
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External power frequency magnetic field-induced jitter on computer monitors
- 1993
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Ingår i: Behaviour & Information Technology. - : Taylor & Francis. - 0144-929X .- 1362-3001. ; 12:6, s. 359-363
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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.
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