Windows ... architectural development... takeover of artificial lighting ... renewal of interest in daylight ... energy use ... passive architecture ... strategy ... control

'It is impossible to overestimate the important influence of natural light on the interior and exterior forms of buildings and on those who dwell in them. So daylight is the natural beginning'1.

From the earliest caves, daylight informed the lives of the inhabitants, initially in the difference between night and day; but as dwellings became more sophisticated, by means of openings or windows letting in light.

The history of architecture is synonymous with the history of the window and of daylighting from the initial crude openings, letting in light and air, heat and cold, the window was the vehicle for the introduction of daylight, and ultimately to the wondrous interiors of the mediaeval cathedral, the Baroque churches or the many private buildings of the eighteenth century.

The window has developed over the centuries, but its purpose of letting in daylight has remained its primary role; window openings required a suitable infill to modify the external climate. At first various materials were used, such as thin slabs of marble, sheets of mica or oiled paper, but it was not until the development of glass for windows that substantial progress could really be made.

Glass had been discovered as early as 3000 bc in Egypt, and was used for decorative objects, but it is known that small panes of hand-blown glass set into bronze frames were used for the infill to window openings during the Roman period. These were little different to the leaded lights of the mediaeval period, being limited to the small pane sizes governed by the manufacturing process.

It was left until the seventeenth century for large panes of glass to be developed in England and for larger windows to be made possible.

The history of windows is really the history of architecture, from the crude openings in the sides of early domestic buildings open to the atmosphere, or openings in the roof construction, allowing the entry of rain collected in a central pool.

1Lighting Historic Buildings. Architectural Press. 1997

The appearance of buildings of all periods reflects the nature of the windows, in some cases such as the mediaeval period, the shape and location of the windows being functionally related to the role played by daylighting, whilst in the renaissance period the location and form of windows became more formalized, often being less well related to the interior spaces they served ... the elevation, the appearance of the building seen from the outside, became of prime importance, a consideration which lingers on today.

Windows have always led to innovation, and this can be seen in the stained glass windows of the great mediaeval cathedrals, telling the Christian story, where whole walls of glass were made possible by structures such as the flying buttress.

Windows had to serve military needs in fortifed buildings, leading to slit windows from which arrows could be fired; with splayed sides having the desirable effect of reducing the contrast between the brightness of the window and the interior wall surface, a device which has continuing validity.

A further innovative means of daylighting was that developed for the lighting of the Baroque churches of southern Germany, where 'indirect' daylight onto the ornate decorations and ornaments of the church is gained from windows concealed from the direct view of the congregation. Indirect daylighting is equally valid today, as used by Basil Spence at Coventry Cathedral, or by Jorn Utson at the Bagsvaerd Church in Denmark2.

Whilst the vertical windows set into the outside walls of buildings were clearly of the first importance, and continue to be so today, it was the roof lights allowing daylight into the central parts of buildings that had an important influence on the plan form of the stately homes of the seventeenth and eighteenth centuries. These took several forms, from domes such as that at Keddleston Hall (1759) where light enters from the top or Chiswick House (1725) where the dome is surrounded by windows in the sides, in both cases the method of daylighting allowed architects to have more flexibility to plan the central areas of their buildings. It is of interest that this method of introducing daylight to the centre of buildings has a resonance with the atria which we see in many buildings today.

The modern movement in England in the 1930s used the new methods of construction available, to allow an entirely new approach in residential buildings, with whole walls of glass and wrap-around windows at corners to express the freedom of the relationship between inside and outside, a freedom which was ultimately expressed in the walls of glass now possible in tall commercial structures.

Daylighting remained the primary means of lighting to all types of building until the early twentieth century, when for various reasons, not least the greater efficiency in the development of electric sources, the primary role of daylighting was beginning to be questioned.

The growth of the workplace in the nineteenth century had seen buildings requiring higher levels of light, and this was achieved by planning long horizontal windows, where the daylight close to the window wall would have been sufficient, but with the pressure to reduce the floor to floor height for economies of structure, even this became insufficient.

2Lighting Modern Buildings. Architectural Press.

The pressure to increase the levels of light in buildings came from the utility companies, who saw this as a means of increasing the sale of electricity, and for the manufacturers the sale of lamps and equipment. Up to a point this was a benign influence, although the effect in the USA went too far, with levels of 1000 Lux and above recommended where far less was sufficient.

By the 1960s the concept had grown that ultimately, if not immediately, artificial or electric lighting would supplant natural light as the primary source during the day in the work situation.

Quoting from the author's own book written in 1964:

'It is inevitable that artificial light must become the primary light source where efficiency of vision is combined with an economic analysis of building function. Natural lighting is becoming a luxury.'3.

The fact that this was not deemed stupid at the time is a measure of how far down the road of the controlled environment life had become.

There was in fact substantial evidence to support this view for the lighting in offices, factories and other buildings where difficult visual tasks need to be done. Economies of structure had meant that ceiling heights had been lowered, reducing the penetration of daylight into buildings. A government 'low cost energy policy' determined that the price of electricity was not a major factor in the running costs of such buildings, and that therefore an economic case could be made.

By the 1960s a professor of architecture stated that the first decision an architect had to make when planning a new building was the level of light and the nature of the electric light source to achieve this.4 ... daylight was to be disregarded as a functional source. This led to windowless factories, and even windowless schools, the ultimate idiocy. It was even mooted that buildings could be heated by the means of lighting, leading to artificial lighting being used at all times of day, even when the heat generated had to be wasted, by dispersal.

This was an 'engineering-led approach' and some architects tended to be carried along with it, although it must be said that the more thoughtful architects resisted.

It was not until the energy crisis, and the realization that our reliance on fossil fuels had limitations, that people started to question this high energy approach, and began to look at ways to reduce the electricity load in buildings, and one of the more obvious ways was to return to an understanding of the natural resource of daylight.

Clearly daylight is not cost free, and factors such as the control of sunlight, heat gain and loss, the association of windows with ventilation and the question of whether the windows should open or the building be sealed, are all problems which need to be addressed; but these need to be equated with the human desire for association with the natural environment, as well as the possible savings in electricity and cost.

It is useful to state some of the reasons why the association with the natural environment has been important, seen through the hindsight of history.

1. First there is the question of light for seeing in order to function within a space. This must vary according to the type of building, whether

3Lighting in Architectural Design. McGraw-Hill. 1964. Pub.USA

4Prof. Alex Hardy.

a residence, an office or a factory ... the need may be to read a book, operate a piece of machinery, or whatever. If it is possible for daylight to provide this, then we expect it to do so.

2. The natural appearance of a space, where the overall experience, the objects and surfaces, are modelled in daylight together with the addition of sunlight at certain times of day.

3. The cyclical change from morning to evening, changes which are varied still further with the weather and the season of the year. Man has an innate desire for variety and change in his environment, and changes in the appearance of a space from time to time provide this.

4. The orientation which comes with the knowledge of a person's whereabouts in relation to the outside world. In a totally artificial environment, a person has difficulty in finding his way inside a building, a problem which was evident in some of the early artificially lit shopping centres, where people became disoriented, having problems in finding their way around the building.

5. The experience of the world beyond the building, by the view to the outside, whilst this is associated with the factor of orientation, it has the added aspect of content . . . which can be of open countryside, trees and landscape, but more often than not of other buildings and street patterns. What is important is not only the content but also the experience of something at a distance as a rest centre for the eye. Daylight is clearly crucial.

6. The experience of natural colour; for whilst the physical colour of our world as experienced in daylight changes from morning to night, the changes are a part of our experience; we compensate automatically, a white wall appears a white wall even if in the evening it may be warmer, or is coloured by sunlight, or altered by cloud formations . . . it is the colour we regard as natural.

7. Although perhaps not essential, it is a part of the experience of the natural world that we should be able to receive natural ventilation, by opening windows. This is a part of the human desire for control of his environment, whether this be the light on his work, or the air that he breathes.

On the whole architects had not submitted easily to the tendency towards the totally artificial environment leading inevitably toward air-conditioning in larger projects; but tended to be overruled by engineers; however research work carried out in Britain by Prof. Hopkinson at the Building Research Station in the 1950s developed the concept of PSALI or Permanent Supplementary Artificial Lighting for Interiors5.

The concept behind this research was that provided daylight at the side of the room closest to the window was adequate, the fall-off of light furthest from the window could be supplemented by electric sources.

This provided for the historic advantages of daylight listed earlier, most particularly in providing the impression that the whole room was daylit, although it was not, permitting the concept of the 'well lit room'. Whilst this did not have the immediate effect of reinstating daylight as a primary source it was left to other outside influences to reinforce the architect's renewed interest in the subject.

The outside influences were to some extent political, the sharp increase in oil prices and the fuel crisis, the gradual realization that the fossil fuels

5Paper by Ralph Hopkinson and James Longmore. PSALI. 1959

upon which the world relied, the coal and oil, had a finite life and once used were not replaceable. No doubt this would have been ignored apart from the further factor of a greater understanding of the greenhouse effect due to the release of carbon dioxide by the burning of those same fossil fuels. Finally there was the destruction of the ozone layer and the increasing danger of global warming.

For these reasons some nations took account of the need for an intense look at alternative means of energy, by means of wind and wave, and the use of hydroelectric power where this was possible.

This was all taking place at a time when the amount of energy in buildings was increasing, by means of the greater introduction of air-conditioning to a point when it was apparent that buildings had become the greatest single form of atmospheric pollution. Whilst this was clearly the prime mover in calling a pause to the rise in the use of energy in buildings, the role of the historic advantages of daylight were not insignificant, the human factors demanding a closer look.

The historic result of this was that buildings, analysed as the greatest cause of the problem, came under intense scrutiny; the words 'passive building' and 'sustainable architecture' became of greater importance. People began to seek ways to reduce the use of energy in buildings, and the prime suspect became the energy used for lighting.

Passive architecture, is where the structure of the building is designed in such a manner as to reduce the need for mechanical controls of heat, light and sound to a minimum: the term 'Net Zero Energy Demand' or a situation where 'the energy consumed equals the energy harvested.'

Daylight and sunlight are at the heart of this new philosophy; they arrive every day in greater or lesser quantity, and provide power for lighting in two ways. First they enter the building through openings as 'light' to the interior spaces and second they impact with the exterior building surfaces, and can be translated into energy by means of solar conversion.

What it does mean is that daylight must be at the centre of the architect's strategy by the orientation of the building, by the nature of the apertures, indeed the whole structure of the building.

This brings us back to the question of the infill of the apertures, at the building's perimeter ... this is no longer glass just to keep out the weather, but a very sophisticated window element which may be designed to restrict or harvest the exterior energy, by means of selected coatings, photovoltaics, cavity fills and advanced blind systems and controls. It is in such ways that the amount of energy used for lighting can be substantially reduced, contributing towards the ideal suggested of 'net zero energy demand'.

It is clear that daylighting is at the heart of the equation, requiring a holistic approach to design, in which the human factors outlined above can now be placed in the correct order of priority; it is no longer true (if it ever was) that daylight is a luxury concerned with the view out of the window, although the view out of the window is an essential part of the role that daylight must play.

In David Lloyd Jones's thoughtful book Architecture and the Environment, he defines sustainability in architecture as

'development that meets the needs of the present, and is at least as valuable to future generations as the value of the environmental exploitation that results . . . a sustainable building (in energy terms) is one that over its life breaks even or is in credit in respect of energy consumption.'

If daylight is to be at the heart of this equation, then the use of energy for artificial lighting in buildings must be reduced by the intelligent use of daylighting design; since it is now possible for the deficit in energy to be made up by means of solar conversion ... the use of photovoltaics, powerful enough to generate sufficient energy to meet or exceed its lifetime consumption.

Sustainable architecture is associated with minimizing all the different aspects of energy consumption associated with the production of a building from materials to construction methods and transportation, together with the continuing operation of the building throughout its life; but it is with the energy used for artificial lighting and the possible economies associated with sunlight and daylight that we are concerned with here . . . the development of a strategy for design, a strategy which involves all the relevant criteria leading towards a holistic solution.

If we ignore the demands made upon a 'passive' structure, by aspects of ventilation, air pollution, and the artificial lighting system, it is possible to outline a simple four-point strategy for daylighting design, bearing in mind that all the other factors need to be borne in mind to complete a holistic approach towards the building design.

1. A decision needs to be made on the siting of the building, differing as to its location and site characteristics; in a green field or urban situation; taking into account the orientation, sun path and location of existing buildings or landscape.

2. The building function may determine the room dimensions, heights, and subdivisions, bearing in mind the present and future needs of occupation. Room height is a key decision, having a bearing on daylight penetration and the desirable overall room depth as well as building costs.

3. The window size and disposition. This is clearly the most complicated design decision, since it must incorporate all the human factors mentioned earlier, such as the provision of view, control of heat gain and loss and the elimination of glare, as well as the more obvious needs of functional vision.

The combined windows should provide an average 5 per cent daylight factor for a substantial part of the floor space. From the architect's viewpoint, this may well appear as the most important decision, since it will determine the appearance of the building elevations from the exterior; but from a strategic point of view it will determine the success of the daylighting approach.

It will be advisable to prepare a specification for the windows to include the nature of the glass, its transmission value and other characteristics. The types of glass are discussed in some detail under the subject of energy later, but it is at this point that the needs of other disciplines must be integrated, such as ventilation, sound attenuation and energy conversion (PVs).

4. Finally control systems are a consideration, first, those controls which relate to the outside condition, the control of sunlight and the avoidance of glare; and second, those of the interior, the relationship with daylight and the artificial lighting system, to facilitate 'daylight linking'; this will be crucial to effect the possible savings in energy.

Whilst the four-fold decisions outlined are a necessary start, they must at each point be related to the other criteria for building design, not least of which will be the question of structural possibility, durability and its relationship to overall building costs, both initial and running costs, which relate to overall sustainability.

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