Elżbieta Janosik
Health aspects of lighting used in households
Zdrowotne aspekty oświetlenia stosowanego w mieszkaniach
Zakład Szkodliwości Fizycznych, Fizjologii Pracy i Ergonomii, Instytut Medycyny Pracy i Zdrowia Środowiskowego w Sosnowcu
Streszczenie
Światło i jego praktyczne zastosowanie w formie oświetlenia odgrywa istotną rolę w życiu człowieka, ponieważ generuje wrażenia wzrokowe, kształtuje doznania psychiczne i rytm funkcji życiowych. Sposób, w jaki światło determinuje możliwości wizualne i reakcje fizjologiczne, zależy od właściwości oddziałujących bodźców świetlnych. W artykule podano drogi oddziaływania światła na człowieka, omówiono ilościowe i jakościowe parametry oświetleniowe kształtujące warunki widzenia i klimat świetlny we wnętrzach oraz podkreślono możliwe negatywne skutki zdrowotne niedoboru lub nadmiaru bodźców świetlnych w otoczeniu. Przybliżono także, z uwzględnieniem aspektu ekologicznego, zalety i wady nowoczesnych źródeł oświetleniowych stosowanych do oświetlenia mieszkań. Ponieważ światło wpływa na sprawność widzenia, samopoczucie, a nawet zdrowie człowieka, dobre oświetlenie można uznać za podstawową potrzebę w naszym życiu codziennym. Redukcję szkód wywołanych nieprawidłowymi warunkami oświetleniowymi można osiągnąć, stosując się do zaleceń podanych w artykule oraz korzystając ze wskazówek osób zajmujących się kreowaniem oświetlenia we wnętrzach.
Summary
Light and its practical application in the form of lighting plays an important role in human life, because it generates visual impressions, shapes mental experiences and the rhythm of vital functions. The way in which light determines visual capabilities and physiological reactions depends on the properties of the interacting light stimuli. The article presents the ways of its influence on human beings, quantitative and qualitative lighting parameters shaping the visual conditions and the light climate in the interiors were discussed, and possible negative health effects of deficiency or excess light stimuli in the environment were underlined. The advantages and disadvantages of modern lighting sources used for housing lighting have also been approached, taking into account the ecological aspect. Because light affects the efficiency of vision, well-being, and even human health, good lighting can be considered as a basic need in our everyday life. The reduction of damages caused by incorrect lighting conditions can be achieved by following the recommendations given in this article and using the instructions given by the interior lighting creators.
Introduction
Light plays a key role in human life. Light stimuli, through the organ of sight, provide people with over 80% of information about the surrounding environment (1). In addition to generating visual impressions, the influence of light on the physiology of the human body is also important. The changes of light shape the rhythm of its vital functions and evoke specific mental experiences. In everyday life, one can observe that lighting too strong, especially an artificial one, causes irritation, while darkening of lighting, in certain situations, promotes relaxation. In addition, during spring and summer, we are generally full of energy, while during fall and winter our activity decreases. There may also be other effects of lighting impact on the well-being and even human health, which we are not always aware of, and which depend on the quantitative and qualitative properties of the interacting light stimuli. Therefore, it is very important to know how to apply the light properly in places where the contemporary man stays the longest, ie. in households, schools and at work.
Light is electromagnetic radiation with wavelengths in the 380-780 nm range. These waves have the ability to evoke visual impressions in the human eye, therefore the light is called visible radiation (2, 3).
The evolutionary conditions of life on Earth make the human body needs the entire spectrum of sunlight (4). Also, the human vision was adapted to receive the entire range of visible radiation intensity of the Sun reaching the Earth (5).
The ways of the interaction of light on the human body
The course of the human vision process is well recognized. The classic path of light stimulus causing visual impression is: the optic system of the eye, retina (where the light stimulus is transformed into a nerve stimulus), optic nerve, visual intersection, visual band, lateral geniculate body, visual radius and visual cortex of the occipital lobe (6), which follows the final visual perception.
The share of visible radiation in the regulation of physiological processes in the human body is slightly less known. The human body is equipped with an endocrine (hormonal) system that activates various human body systems, adapting them to changing environmental conditions (6). Endocrine interferences are made by hormones that are transmitted through the blood to the target cells, where they regulate many vital processes. As established, the endocrine gland characterized by a significant sensitivity to light stimuli is pineal gland. During the aforementioned visual path, a part of the visual-ganglion neurons leaves the visual junction, running directly to the suprachiasmatic nucleus of the hypothalamus, and from there through the spinal cord and the upper cervical ganglion form connections with the pineal gland (fig. 1), which in turn secretes hormones – serotonin and melatonin (6, 7).
Fig. 1. The way light affects the pineal gland
In the absence of light stimuli, the secretion of melatonin increases, while light inhibits its secretion (secretion), triggering serotonin production.
Melatonin of pineal origin is released into the bloodstream and then reaches all organs. An adult emits 12.3-28.8 μg of melatonin daily, and the concentration of this hormone in the blood varies from 0-20 pg/ml during the day to 80-150 pg/ml during the night (7, 8). The balance between the melatonin and serotonin secretion cycles is essential for maintaining the so-called clock/biological rhythm (24-hour of activity and rest cycle). This innate ability to measure time helps the body to adapt its activities to the time when their performance is most important. For example: when the evening falls, the amount of melatonin increases. Melatonin, reaching the appropriate receptors, lowers body temperature, which makes falling asleep much easier (9).
The amount and quality of light needed for the effective functioning of the body
Proper lighting – using natural (solar) or artificial light – determines the efficiency and comfort of vision. Interior lighting technology is based on knowledge about human psychophysiology. Taking into account the properties of the human eye, it has been established that in order to obtain a good quality of vision one should assure (10):
– sufficient levels of light intensity – to allow/facilitate perception,
– uniformity of light intensity, uniform distribution of luminance in the vision field and limiting the phenomenon of glare – not to overload the eyes adaptive mechanisms and provide visual comfort,
– the appropriate colour of light and the appropriate light-rendering ability of used lighting sources – to provide the appropriate light climate, generate psychological feelings, facilitate the perception of colour sensations.
When designing the lighting of a given room, first it is determined what function it performs, how precise visual works are carried out in it, and then based on the lighting standards, the values of the above lighting parameters are selected.
The place where people spend most of their time after work or study are households. Inhabitants lighting issues are usually solved intuitively, because on the issues of house lighting they do not pay too much attention, or do not know how they can provide optimal lighting in their households. However, familiarity with the basic principles of proper lighting can help taking right decisions about lighting solutions.
The basic requirement is to provide adequate levels of lighting intensity on the main areas of work and walking routes. Taking into account the minimum values of illuminance for various activities and rooms given in Polish Standards PN-84/E-02033 or PN-EN 12464-1 (11, 12), it is possible to determine lighting levels suitable for rooms/home situations (tab. 1).
Tab. 1. Recommended values for illuminance levels in households
| No. | Room/space/activity | Minimal illuminance |
| 1 | corridors, stairs | 50-100 lx |
| 2 | table in the dining room | 200 lx |
| 3 | kitchen countertop/preparing a meal | 300 lx |
| 4 | learning desk | 500 lx |
| 5 | sewing, ansambling small items | 750 lx |
Light in the house should not only facilitate the performance of life activities, but also enable relaxation, affect the well-being of the residents. Not without significance in creating the light climate is the colour of the light used, described by the so-called colour temperature Tb expressed in Kelvin [K] (the value of the colour temperature is given on the holder or packaging of the light source). Light warm white (Tb < 3500 K) has a relaxing and calming effect on humans, while white light (Tb = 3500-5500 K), and even more cool white (Tb > 5500 K) increases concentration and stimulates action. Therefore, light sources with a warm white colour should be used in bedrooms, in places of relaxation, while white/cool white light sources – in places where we perform precise work (writing, sewing, preparing meals).
The visual property is also influenced by the property of light called the colour rendering ability. It is called the so-called colour rendering index Ra. The higher Ra is (Ra takes values from 0 to 100), the better rendered are colours of observed objects, and the objects themselves (even the tone of human skin) look more natural. It is assumed that the best colour rendering index has got natural sunlight. Lighting source, in the light of which the observed colours are not distorted (they look very similar to natural light) has good colour rendering ability and can be used in places where colour discrimination is important (e.g. watching photos, make-up making).
Lighting in the house should be useful, but also adapted to the current needs and individual preferences of its residents. Therefore, it is advisable to illuminate a given residential interior with at least several lighting sources, appropriately arranged and used depending on the situation. In general, it should consist of diffuse general (base) lighting, local (task) lighting and spotlight (decorative) accents. By properly arranging the light fittings of the three types of lighting, choosing the amount, colours and Ra of the applied light, it is possible to create the lighting conditions desired by the residents.
It is a mistake to underestimate the role of proper lighting. An undesirable condition is the so-called underexposure of the interior (13), which may occur due to lack of sunlight resulting from the time of day and season, weather, too small window openings, and in rooms in which artificial light dominates – as a result of poor positioning of lamps, mismatch of the level of illumination to the work performed or individual needs of the user, e.g. people with visual impairments or elderly people.
In many rooms, there are relative lighting conditions at which the user is able to do the work, but this is only possible due to the large adaptation possibilities of the eye and general body’s ability to compensate for poor environmental conditions. These adaptive and compensatory abilities are limited and the effects may be quickly manifested, such as: decreased visual performance, fatigue and eye discomfort, refractive errors, states of depression resulting from gloomy ambient.
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