DAYLIGHT
People’s attitudes to lighting design are paradoxical.Those who have never considered the subject in any depth accept it as part of life and living, requiring little more thought than the strategic placing of some 60-watt “bulbs” and the operation of a switch. And, to a point, they are right. After all, there are very few situations where there is insufficient light by which to see.The danger occurs when a person with this attitude has to make responsible lighting decisions on behalf of other people.
D.C. Pritchard – Language of Light (1)
In the 1940s, the importance of facilitating sunlight penetration into classrooms was restated and a minimum of 2% daylight sky was introduced in 1945 with a memorandum recommending 5% where possible.Sky factor was used then, rather than the daylight factor we use today.Hence, many schools were constructed in the 1950s and 1960s with highly glazed facades.
Unfortunately, many of these school buildings were thermally inefficient lightweight structures, which overheated uncontrollably during summer and suffered high rates of heat loss in Winter.Early system schools were particularly prone to these adverse effects.
The first recorded low energy school in the United Kingdom – St. Mary’s in Wallasey – was built in 1961. This is the only example of a school with no heating system.All heat was provided by Solar pains.(Fig. 4)
The crisis of the oil prices in the 1970s brought about the development of more energy efficient schools and since the early 1980s, a number of schools with low energy features have been built. In the last 25 years, because of improved energy efficiency and other scientific reasons like better like spectra, fluorescent lighting has been almost universally adopted in schools.
The discipline of daylight planning was often neglected as schools were planned to rely on electric light. Energy efficient measures concentrated on reducing heat losses by building with compact plan forums, small window areas and increased fabric insulation.In contrast, a good passive solar design would make much more effective use of ambient daylight thus reducing electricity consumption. A successful solar design involves the optimal balance of maximising daylight and utilising solar energy whilst excluding glare and avoiding overheating.
During the 19th Century and up until the turn of the century, schools were designed to take advantage of north light and so glare from the south or west facing windows was avoided.
In the 1910s to 1930s, there was an awareness of the importance of fresh air and sunlight.This led to the open-air school design movement, schools were oriented in a southerly direction and could employ folding and sliding windows so that teaching areas were exposed to fresh air and direct sunlight for at least some hours of the day.The daylight factor at a point in a room is defined as:The total indoor illumination on a reference plane at that point, expressed as a percentage of that simultaneously obtained out of doors, under a completely unobstructed hemisphere of sky having a luminance distribution in accordance with the definition of the international commission on lighting (C.I.E.) for a standard overcast sky, the effects of direct sunlight being excluded (2)
Direct sunlight in some areas such as entrance halls can contribute to the quality of the space. But on the other hand, the entry of beams of direct sunlight can be a source of discomfort and glare. (Fig. 5)
If sunlight is diffused or directed onto the ceiling or walls, then it can be a worthwhile contribution to lighting requirements.Rooflights are commonly used in buildings, to make the most of natural daylighting, for example the museum in Grenoble which was designed by Group 6 Architects, the aim was to design the roof apertures so that optimal natural light fell on the paintings (Fig. 6) The daylight factors in the range 0.7% to 1.5% so that degradation was reduced but there was insufficient illumination for display, illuminance of a surface will depend both on its reflection factor and upon the illumination falling on it. The surface’s apparent brightness to the observer will also be affected by the level of the eye.
In most schools, it is possible without undue expense to light all teaching space to a good standard by natural means, with the artificial lighting installation only being used to supplement daylight occasionally, on the dullest days.Buildings with normal ceiling heights, good daylighting can be provided in rooms lit from the side only, which are not deeper than 6m to 7.5m, or in rooms lit from more than one side not deeper than 9m to 10.5m. In rooms deeper than stated or which are of low ceiling it is often possible to provide additional lighting from a roof light.Hopkinson states: –
Good daylight is something most people like to have; it induces a feeling of well being and freshness, which, at the present time, even the best artificial light cannot.This point must constantly be borne in mind in what now follows.It would be tedious to reiterate it, but whenever we treat lighting purely in physical, quantitative terms, as we are now doing, we must constantly sit back and think of the implications of where our calculations are leading us. If they lead us to a design which common sense and experience tell us will be disliked, there is no choice but to examine the design on those grounds and to reject it if it is clearly at fault – R.G. Hopkinson (3).
In an ideal world, it is not practical to light a building only by the aid of daylighting, but to produce an integrated lighting scheme in which natural and artificial lighting is combined so that predominantly artificial lighting at a distance from the window does not appear to the users of the room to be deficient in quantity or quality when compared with natural lighting near to the windows.
In determining the quantity and quality of daylight in schools, it is advised to take note:the conditions of the existing site, the educational needs of the room and the economic considerations.These influences on the design may not always be compatible.
Creating a building that has a high standard of lighting during the day can be met in two ways: –
(i)Full daylighting, which requires a building with a complicated coastline and section;
(ii)The use in the deep rooms of which may still be the most satisfactory lighting solution, considering the building as a whole.
In the same way, the lighting requirements of the individual rooms will interact with the overriding needs of the whole school and as Colin Stansfield states:
Many old people’s homes, for example, seem to be designed more for the staff than the residents; de-personalised and easy to clean, and frequently built to a standardised plan despite using traditional construction which could have offered freedom from the routine.Maintenance and design were seen as separate issues and it was not uncommon to find a fine Victorian school re-rooted with coarse concrete tiles, or extended with a system-built block utterly insensitive to the materials and characters of the existing building – Colin Stansfield Smith (4)
The activities of the end user should be put first and an understanding of their visual needs:when considering the lighting of a school building. The majority of classrooms in schools were designed for groups of thirty to forty children in rooms of 500 sq ft to 650 sq ft, arranged mainly for formal teaching with the children seated at their desks and facing in one direction.The use of the rooms is, therefore, static and the lighting problem a relatively simple one.
An interior, which is lit by daylight, has some advantages over that which is artificially lit which includes that:
I.Light from a window falls horizontally across the room, making a useful contribution to modelling and softening the shadows cast by overhead lighting.
IIA view through a window provides a distant visual release and avoids an oppressive sense of enclosure, and finally that the sun and sky, the clouds and wind, and the play of light and shade outside are never static and a window is a link with the interest of the constantly changing world out of the doors.
- Create work spaces with good task visibility and visual comfort for employees
- Minimise energy consumption by specifying energy-efficient lamps, ballasts, luminaries and controls
- Achieve bright, visually stimulating spaces to help keep workers alert in early morning hours;
- Keep the initial cost of the lighting installation within budget; and
- Install energy-efficient lighting products
Daylight first played its major role in sacred buildings and the admission of light through the massive elements of the fabric covered symbolism, which was irresistible to the architects of the great churches and cathedrals.It was in sacred buildings too that glass made the earliest impact; the use of stained glass in the great cathedrals was widespread by the 12th Century.The technique was pioneered in France and Germany and artisans from these countries often travelled Europe-wide to trade their wares and sell their skills. It is difficult to overstate the impact that a sunlit, stained glass window, of majestic proportions would have had on an illiterate peasant.For the task of promoting religious beliefs, it was “state of the art” remaining unchallenged for its visual impact until the cinema, nine centuries later.
Gradually, glass manufacturing became more established and costs came down.The land-owning classes were the first to adopt glazing, as violence and strife subsided and the fortification of their dwellings became of lower priority.Windows began to be larger and by the 16th Century we see the celebration of windows, as typified by the oriel windows in the Cambridge Hall (Fig. 27), Church in Medina, Malta (Fig. 28), Queen’s College, Cambridge (Fig. 29), Corpus Christ, Oxford College Library (Fig. 30) and the Clevestory windows at Guildhall in Lavenham, UK (Fig. 31)
It was in spinning and weaving that the saw most impact on building design.The need for light would have meant that production was crucially dependent upon prolonging the availability of daylight to a maximum.It must be realised that in the 15th Century, the real cost of artificial light was about 6000 times more than today (in relation to living costs).
Even before industrialisation, there were certain indoor activities that made real technical demands on daylighting. Writing, printing and painting all would have needed good light and with only primitive artificial lighting available, there would have been a heavy reliance on daylight.
Despite the increase in the use of glass in the 17th Century, mainly in the form of small by modern standards.This was partly due to structural limitation, especially in masonry buildings, although in grand architecture amazing structural features were achieved with stones and even moulded brick mullions.
Even though we look upon daylight as our principal source of light, it is important to remember that, especially in southern countries, it may be difficult to use directly in everyday working life because of its high intensities and constant variation due to sunpaths and meteorological changes.It is important therefore that architects envisage the visible environment as highly structured, three-dimensional light fields.Architecture becomes the shaping of this future luminance field.
Studies on lighting have considered artificial and natural light as equivalent, addressing merely the illuminance level.Studies had also shown to illustrate to what extent daylight is preferred over artificial lighting sources, making its quality as an illuminant an important reason for using it in buildings.Daylight, which is the combination of sunlight and skylight, is the light source that most closely matches human visual responses unlike artificial lighting. Years ago, the human eye evolved using this light spectrum as the source against which all other light sources are compared, thus daylight is likely to provide the best visual environment.
Often, designers are unable to determine whether a space is sufficiently illuminated or too dark. It is important to realise that the way surfaces are illuminated is often more important than how much light falls on them.
Taking all these points and realising the way technology takes over society, we are torn between good health and advanced technology.And taking all other aspects of life, we are known to select technology over good health as long as the technology makes our life easier, even for just a little while.
Most of the advances in science and industry during the past hundred years have been improvements in technique leading to lower production costs.Chemical industries pollute air and water and it is only afterward, when the damage becomes unbearable that measures have been taken to reduce the harmful effects.Insecticides and chemical fertilisers disturb the balance of nature and are exterminating more and more species.The automobile industry produces more and more cars: it was only after half a century in some attention being paid to safety and to the complete combustion of petrol.
Environmental problems these days can largely be met with the aid of instruments and formulae available now, but still insufficient attention is being paid to the factors that bear on the positive well being of the individual, completely ignoring the psychological factors.
The whole development of the technique of lighting up to this day has been inspired by the 19th Century conceptions of society, ignoring completely the well being of the worker and letting commercial interests dominate all research.
The future of daylighting looks more blink than bright.Due to the problems that dominate daylighting, there is the fact that accuracy is limited by the superficial treatment of the optical physics involved and its being commonly acknowledged that many daylight control implementations do not produce internal conditions that satisfy the occupants’ comfort criteria. The potential for energy-saving and improved internal comfort is apparent, but the means through which they can be achieved is less obvious.The ability to simulate accurately a wider range of architectural design options would undoubtedly help to establish those criteria that have the potential to provide the requisite benefits, otherwise the future of lighting hangs in the hands of new technology and heading to the end of daylighting schools even though the negative effects are obvious.The dynamic nature of daylighting needs to be understood and also the occupants’ reaction to time rate change, spatial distribution and relative contrasts caused by daylight in an enclosure.