Browsing by Author "Bergqvist, Ulf"

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    Belysning och hälsa : en kunskapsöversikt med fokus på ljusets modulation, spektralfördelning och dess kronobiologiska betydelse
    (Arbetslivsinstitutet, 2002) Sandström, Monica; Bergqvist, Ulf; Küller, Rickard; Laike, Thorbjörn; Ottosson, Allan; Wibom, Roger
    Lighting and health : a review of the state of knowledge of light with focus on spectral power distribution, degree of modulation and chronobiological impact This document reviews the state of knowledge concerning health- and disturbance effects of different light sources. The paper focus on three aspects of light: spectral power distribution, degree of modulation, and thereby flicker, and chronobiological impact. How visible light appears and the effect of the radiation is dependent on how the light is generated. Therefore, a technical description of the different light sources is an important part of this work. Similarly, conceptions and terms of importance for the visual function and perception of light are described. In physical terms, visual light is a part of the optical radiation, which also includes ultraviolet light (UV) and infrared light (IR). In this paper, only visible light defined as electromagnetic radiation in wavelengths from 400 to 780 nm, defined by CIE (International Commission on Illumination), is included. Spectral power distribution Different light sources emit light at different wavelengths within the visible part of the spectrum as well as in other parts of the optical radiation (UV-, IR-radiation). Discharge lamps produce primary light in certain distinguished wavelengths that partly are in the UV range. Through secondary processes in the fluorescent tube, the UV radiation converts into continuous light in the visual part of the spectrum. Depending on the type of phosphor used in the tube, different spectral power distribution (SPD) will appear. SPD from a cathode-ray tube based video display unit (VDU) screen is defined by the phosphor that has been used. SPD of modern multicolour screens varies to be able to produce different colour tones. The SPD-curve show graphically how a light source distributes the radiation in the visible frequency range. In a large number of field- and laboratory studies the impact of SPD on visual function, performance, health or well-being have been studied. The investigations have primarily focused on whether artificial light with a SPD equivalent to daylight is superior to light with other SPD. The review of the actual research in this area has not been able to give a distinct answer to that question. Light modulation Our experience of light modulation (a periodic fluctuation of luminance) is called flicker and is in principle visual, i.e. we can detect it with our visual system. When the frequency of the flicker is high enough, it is interpreted by us as a continuum. The degree of modulation varies between different light sources depending how the light is generated, and can sometime be up to 100 per cent. So called high frequency light, for example fluorescent tubes with high frequency gear, has a fundamental frequency of 30-50 kHz and can be classified as a flicker free light source. If a cathode-ray tube based VDU screen has a refresh rate high enough, the picture on the screen appears flicker-free even though the picture has 100 per cent degree of modulation. Liquid crystal screens are in principal flicker-free. A review of studies concerning non-visual flicker from fluorescent tubes indicate that certain sensitive persons are affected negatively by the flicker. There is no existing explanatory model as to why certain people (even, sometimes, healthy people) show a stronger response to non-visual flicker compare to controls. It is however obvious that the arousal of the central nervous system might give negative effects. The appearance of detectable flicker on the VDU screen might be a factor of importance for the appearance of VDU related symptoms and is probably more pronounced during data input, when the eyes are focused beside the screen. To counteract this the refresh rate should be high. The impact of light on chronobiology The circadian timing system of humans is synchronized to the 24-hour day and includes, for instance sleep, awakens, body temperature, metabolism, hormone production as well as fluctuations in awareness and behaviour. The control of these functions and processes are driven by the nervous and endocrine system and is commonly called the biological clock . Although the non visual effects of light on humans have been known for a long time it is only during the last few years is has been included in light planning. The biological clock is synchronized with the rhythm of the sunlight, especially in the morning and evening. A review of the literature show that for people who are indoor it is of importance to have access to daylight through window especially during wintertime. Being in windowless rooms or being in dark rooms might have negative consequences for well-being and capacity for work. Both artificial as well as natural light seem to have an impact on the biological clock. Conclusion A review of the literature in this area of research can be summarised by the following items: - There are a number of studies showing that non-visual flicker has a negative impact on humans. Therefore, as a precautionary principle, installations of high frequency light type are to be recommended. - Access to daylight has, in a number of studies, been shown to be of importance for health, well-being and performance and should bee included in light planning to be utilized in the best way. - Studies of light with a spectral distribution equivalent to daylight have not been able to verify that visual functions, capacity, health and well-being are positively affected of this light compare to light with other spectral distributions. - Detectable flicker on the VDU screen might be one factor that causes eye discomfort. In order to avoid that, the refresh rate of the screen should be high. Key words: flicker, video display unit, light source, eye discomfort, the circadian timing system, the biological clock, perception, daylight.
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    Ultraviolett strålning och hälsa : ett kunskapsunderlag
    (Arbetslivsinstitutet, 2002) Nylén, Per; Bergqvist, Ulf; Fischer, Torkel; Glansholm, Anders; Hansson, Johan; Surakka, Jouni; Söderberg, Per; Wester, Ulf
    Ultraviolet radiation and health Exposure to ultraviolet radiation can cause adverse effects on skin, eyes, and the immune system. Some effects are acute : they appear after short duration of exposure to ultraviolet radiation. Such effects are erythema, increased pigmentation, photokeratitis and photoconjunctivitis. Other effects such as elastosis and certain forms of skin cancer are regarded as irreversible and appear after chronic exposure. The acute effects and the photoageing of the skin are commonly occurring, while the more serious cancer forms are less common : but their occurrences have increased in recent years. This is considered to be at least partly attributed to an increased exposure to ultraviolet radiation. Thus, there is an obvious need to limit the total exposure to ultraviolet radiation. Internationally, ICNIRP have developed guidelines for the limitation of exposure to ultraviolet radiation. These limitations give individuals with normal sensitivity a protection against acute effects on skin and eyes, and are also thought to protect against some of the long-term effect (e.g. certain cancer forms). Several forms of malignant melanoma are, on the other hand, thought to be a result of single episodes of heavy exposure. High levels of UV radiation can occur within Swedish industry at e.g. welding and UV curing of surface coatings. The possibilities to locally measure and control these levels at a relevant cost have improved during the last decade.