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Lightning Design process

Introduction

Lighting design is a process of informed decision making, involving a sequence of creative and practical choices that support the goals of the project. This chapter introduces the design steps and some considerations essential for successful results.

Overview

Lighting design is the creative process for developing lighting solutions for safe, productive and enjoyable use of the built environment. In the past there has been an overwhelming emphasis on assuring that an appropriate quantity of light is delivered to the task or work surface. Quality of light has been considered mainly in the limited sense of controlling direct glare from luminaries or reflected glare from surfaces and objects. However, lighting design extends far beyond these factors. Light is one of the tools used to shape our environment, visually and emotionally. Lightning a synthesis of light and shadow, color, form, space, rhythm, texture and proportion, achieved through an understanding of the technology necessary to produce these effects. Working with all of these elements is what distinguishes the work of the lighting designer from that of the artist, from whom the lighting designer draws inspiration; and from that of the engineer, from whom the designer learns practical problem- solving techniques.
Part of the appeal of designing with light is its elusive nature: its effect can be almost palpable and may be visually arresting, yet the rays of light themselves are usually invisible. When designers or users talk of “light,” they often mean the effect of light on a surface or object: highlight and shadow, soft gradations of light, or the sharp definition that comes with focused point sources. Light reveals form: wall planes, three-dimensional space, architectural details, furnishings, sculpture, the breaching structure of trees. Light can enhance or diminish elements of the built environment as well as the natural environment.
Light profoundly affects our feelings of well-being, of awe and wonder, of mood, of comfort, of motivation. It influances how we perceive all the other elements. Light patterns evoke psychological responses such as “bright,” “dim,” “magical,” “dull,” “mysterious,” “pleasant” and “forbidding.”

‘’The associations we have with light are inevitably made early on, more so than with many other aspects of architecture. Light can symbolize dignity and mystery to those who first became aware of its special qualities in the soft, mysterious light of a church. It can symbolize excitement to those whose early memories of light are the dazzling, never touchable lights of Broadway or Times Square, to those to whom the glow of neon marked the first place in which they realized that light was much more than what happened when you flipped a wall switch. On the other hand, light can symbolize comfort and security to those whose recollections are of lamps left on at night to guide them home or just to make a house feel warm. And comfort mixed with a hint of the exotic, for those whose early memories are of candlelight and the glow of a fire.’’

‘’ What is most important about all of these things is that they deal with emotional associations. They are not pure fact, the recollection of the knowledge that one plus one equals two, but something that strikes much deeper than empirical knowledge . .. light inevitably has these kinds of associations for people. However much we can quantify light and talk of things like task lighting, and foot candies, and wattage, light remains an emotional thing. It transcends the scientific, euen as ... designers require more and more scientific knowledge every day. The heart of the issue with lighting is still the emotional associations it engenders, the way lighting "feelf." For what changes in a room when the lighting changes are not the hard facts, not the length or the width or the height or where the door and windows are. It is the way the room “feels. "’’
Paul Goldberger Address to Lighting World III April 1985  

The Scale of Light

Sophus Frandsen

‘’’Light has a special quality that very few seem to notice. It has scale. In almost the same way that sman objects are overlooked and get lost in a large space, they will tend to get lost if the light is 'large', coming from a large area. Attention simply shifts from detail to totality when light sources become larger. And inversely, it moves from totality to detail when the sources are small.’’’

Consequently all planning of lighting is a continuous rope dancing, balancing the whole against the detail, and involving ambient ision as opposed to focal vision, or feeling of space versus interest in objects
The pictures (figs 1 and 2) can demonstrate the phenomena. They are taken in a small subterranean museum placed in the excavations of the Castle of Copenhagen with a display showing 800 years of development, and a model of the castle as it was in the beginning of the 17th century.
The folded screen is lit from below (and with no overexposure as on the photo). The obvious practical advantage is a minimum of specular reilection and consequently good legibility at a distance. But the effect on the general view is just as essential. The surface is calm, solid but not heavy, and that again creates a feeling of enclosure, permitting the visitors to concentrate on the display. The model of the castle shows a different solution. The small white spots seen in fig. 2 are actually cylindrical black-painted holes concealed in the frames of the glass-case, acting as tiny narrow-beam spotlights. And since it all is so small, and the light is so precise, one can walk around it engaging one's imagination in every picturesque little budding on the roof and the exterior walls. The inner courtyard, since it cannot be studied at close hand, gets a less sophisticated mixture of down lighting and diffuse reflection from the court itself.

Light, form and texture

Now the screen and the model can only illustrate an obvious but rather simple reJation between the size of the object and the size of the light. After all, painted plywood and painted cardboard have virtually no texture.
But when form as well as texture Is Involved, the coordination of the two sizes gets difficult. And that is what the series of three spheres (figs 3.1 to 3.4), each with its own surface-texture, is supposed to show.
The photographs have been taken under an artificial sky and sun, simulated by an infinitely large luminous surface and light from a parabolic mirror. In the silverball it is possible to follow the change of arrangement.

• 3.1) In parallel light the shadows are so sharp and so dense that the spheres almost lose their form. It•s like camouflage. Even the small pits in the orange are big enough to create harsh and disturbing shadows. Only the hairs of the ball and the fibres of the paper stand out in a natural way. But as a result of gloss.
• 3.2) In very diffuse light the lack of shadows means lack of three-dimensional form. The spheres are not spheres, all texture has gone. The tennis ball looks like cotton wool. The orange is remarkably unappetising.
• 3.3) Combining parallel and diffuse light means that the sharp shadows and pronounced texture of fig. 3.1 are kept. But with a density that permits vision to penetrate the shaded areas. The spheres become spheres, although they still may call for some interpretation. The texture is - if not beautiful - at least recognisable.
• 3.4) Parallel light is replaced by a moderately directed one, still in combination with diffuse light from an infinite source. Now the ball becomes really round, soft, downy. Ready for touch. As the orange is ready for eating.

Which shows that - at least on relatively small objects - it should be possible to optimise the lighting of both three-dimensional form and texture. But only by using the trial-and-error method.

A new scale of shadows

Obviously the handling of shadows asks for more than just two words: 'soft' and 'sharp'. But everything in between - actually the overwhelming majority - seems to be without name and explanation. So that is what is proposed here, in a scale of shadows.
The scale itself is simple enough. In principle it is constructed as a grey scale, each step being visually equivalent to all other steps. The scale comprises 10 intervals and 11 types of shadows (fig. 5) each characterised by a specific illumination of three separate areas on the sphere.

1. The top segment facing the circular light source, receiving light from the entire source.
2. The bottom segment, turned away from the light source, receiving no light from the source, i.e. full shadow.
3. The middle zone of the sphere, located between area 1 and area 2, receiving a varying amount of light from the source. Sometimes called the semi-shadow.

Of these the middle zone has the decisive role. It is here the shading occurs from the bright International Lighting Review 1987/3 part to the dark part of the sphere. In completely parallel light there is no shade, only two hemispheres, one 'with and one without light from the source. In totally diffuse light it is all shading, and the gradation extends over the entire surface of the sphere.

All intermediate situations, the individual shadow-types, are then characterised by the size of the shaded middle zone. Which leads us to the following conclusion: It is the size of the middle zone that determines the intervals on the scale. With this as the basis the shadow types can then be given a name and a number: Type 0: zero shading; type 1: 1/10 shading; type 2: 2/10; type 3: 3/10; etc., on to type 9: 9/10 and type lOo 10/10 shading (fig. 5).
Assuming that the circular light sources are very large in relation to the sphere, then the solid angles having the centre of the sphere as their apex will accord with a simple pattern. Their maximum illumination will be determined by the projected solid angle, normally used for daylight calculation. And because of the simple solid-geometry connections, we get: type 0: 0%; type 1: 1 %; type 2: 4%; type 3: 9%; etc., ending with type 9: 81% and type 10: 100%. All the whole squares between 1 and 100 (fig. 6).
It has to be mentioned that the scale is developed in a black room with no reflection, apart from the small horizontal area underneath the balls. On a brighter background all shadowtypes will shift 0.5-1 step up the scale. As in a grey-scale.

What the scale of shadows shows

The visual effects of the nine steps (fig. 4) are obvious. In predominantly parallel light the two balls look as if they were protruding from the picture plane. In diffuse light they get more and more flat. As to the texture, types 1-3 are capable of showing almost every little hair, whereas types 7-9 rather give the impression of a fur.
In the middle, types 4-6 demonstrate their lniddle-of-the-way qualities. Neither dramaticallythree- dimensional nor dull and flat. Showing the structure of the surface, without accentuating more than a few hairs.
The borderlines between the three series are not sharp ones. But for practical purposes it should be possible to consider the whole shadow scale as composed of three separate parts, each with its own properties and expression. The extremes are more or less reserved for artistic purposes. The middle is for everyday use. The shadow-type of fig. 3,4, for example, would in a black room be 3-4, but as a result of the additional diffuse light it is shifted to type 4-5. It should be kept in mind, however, that the scale of' shadows tells us about solid angles and their effect. Which means that the ame angular relations are valid irrespective of the size of the object. The more the physical size of the main form differs from that of the detail, the more difficult it becomes to optimise simultaneously the light on both.
And that conflict is essential. Details are pushed into the background when a large form receives 'large' lighting, Or they can be emphasized by directional lighting, in which case the main form tends to get lost. We cannot expect to get both as a matter of course. So we are forced to make a choice. And that choice will normally be determined by the need for emphasis. Take the orange in fig. 3. It has to look appetising on the dinner table. But in the supermarket we would like to examine it Or take the inspection of a make-up in front of the mirror. It requires revealing light and no flattering. But in the assembly room the opposite would be an advantage,

The Four Shadows

It was mentioned in the introduction: when we see we do it in two different ways, involving focal vision as well as ambient vision.
Basically we are observers. And very often analytical observers, consciously hunting and focusing on big and small details. And in that case there is a need for preCision in form and texture.
But outside the visual axis and its immediate surroundings, focusing has no meaning. We are not observers any longer, we are 'perceivers'. And what we perceive is space. A coherent and continuously changing totality that only occasionally needs our attention. Therefore, exactly the same light that centrally placed means attraction and concentration, could, if placed in the periphery, cause distraction and insecurity. The periphery calls for softness and peace. Which agains means that it should be dominated by relatively diffuse light. It is to handle this problem that the FourShadow concept has been developed. Based on the experience of a normal sidelit room, it categorises prevailing shadows according to their size (see diagram on back coverl:

• A. The big room shadow;
• B. The big object shadow;
• C. The small object shadow;
• D. The small detail/texture shadow.

The terms big and small are to be seen in relation to the size of the human form, specifically the diameter of the human trunk, which seems to be a yardstick in size perception.
In the room the two big shadows, A and to a certain degree B, occur where the daylight is relatively weak, dominated by the light reflected from the suri•aces. The two small shadows, C and D, occur where the day light is relatively strong, dominated by light from the window.
Consequently, the two big shadows are those related to the lighting of the room as such, shadow A in the upper part and shadow B behind the furniture and larger architectural elements.
The two small shadows are those associated with the light on small objects, shadow C on all things we handle, shadow D in the tiniest visible details.
To sum up, the four categories differ from each other in several ways. By their position in the room. By their size. By their illumination level. And one thing more, by their preCision. The smaller the shadow, the stronger the contrast, since the gradation from bright to dark occurs at a decreasing viewing angle.
The perceptual outcome of the four shadows is that the light in the room as such is perceived as being more or less soft, without the sharp transitions that distract and easily get misinterpreted if they occur in peripheral vision. (Who has not stumbled over a step that wasn't there, because a shadow on the floor was misinterpreted?)
Conversely, the light on objects is characterized by a distinctness, which facilitates the perception of three-dimensional form and detail. And if only the reflected light is reasonably balanced, the contrast from light to shade is kept 'within acceptable limits.

The Scale of Light

All that is left is to combine the four shadow categories with the scale of shadows. This could put a new tool within everyone's reach. Shadow planning - indeed functional shadow delineation - would then be a real possibility. With the experience of normal sidelit rooms it is even possible to show the limits for each of the Four Shadows (see fig. 7):

• A. The big room shadow: shadow-types 4.5-10
• B. The big object shadow: shadow-types 3-7
• C. The small object shadow: shadow-types 1.5- 4.5.
• D. The small detail shadow: shadow-types 0-1.5.

These indications are, of course, approximate. The Scale of Light is only a conceptual framework, waiting to be filled with definite knowledge. Not until then will it be possible to describe and predict the spatial and sculptural effect of a lighting scheme, in relation to the total visual field.

The Chariottenborg Gallery

The Scale of Light concept is adaptable to artificallighting as well, as the following example will show. It is an art gallery. And since the walls - according to the concept - should be not only attractive but also calm, the problem is a delicate one.
The gallery was rebuilt in 1980. Until then, two identical rooms showed lighting systems that could be found everywhere. One had spotlights with reflector lamps - and the faults are classical (fig. 8). There is no proper feeling of enclosure. The walls never become the peaceful background that helps the gaze shift from picture to picture and back again. Everywhere the light shadow D - brings out the irregularities in the walls. Frame shadows affect the optical balance of the pictures. Reflections and shadows on the frames distract the attention, and the same may happen locally on the canvas in uneven coatings of paint.

The other room was arranged by a painter a few years earlier for a temporary exhibition. Six or eight frosted 200 watt lamps were suspended so high that glare was avoided. It worked surprisingly well (fig. 9). The upper half of the room acted as one vast luminaire. Shadow A. The picture walls were restful and coherent, without disturbing shadows or reflections from the frames. But with all the necessary small shadows and reflections on the pictures themselves: shadow D, as an extra contribution, and with a solid angle roughly corresponding to 0.1 on the shadow scale. Entirely different from the blufling effect created by reflectors.
However, since the Jightingwas placed so high, the picture zone was appreciably darker than the upper half of the room. And of course the sculptures lacked shadow C.
Our job was to find a solution that without endless changes in the lighting system would be flexible enough to suit almost every thingsmall graphic work, paintings covering whole walls, sculptures and designs of all sizes and materials.

We estimated that large PH three-shade luminaires of 60 cm diameter "vith a differentiated glossy/mat surface would provide a solution1 But then the plane of suspension became much too visible on the wall. And although the luminance difference below and above the plane scarcely exceeded 1: 6, it was hardly possible to look up into the big room shadow.

The next step, a completely mat set of shades, also failed to even out the transition from one to the other side of the suspension plane. And then a new problem turned up. Straight in front of the luminaires there were areas where the oil-painted linen wall-covering totally lost its texture, disturbing the judgement of distance. We named it the 'pillow effect', and found it incredibly sensitive to the distance benveen wall and luminaire.

Gradually, however, we learned how limited a margin there was if, at approximately 200 lux, a tolerable evenness and a reasonable surface texture should be obtained: what we today (in a black room) would call a shadow type l. Even type 1.5 was too diffuse. And then the problem of a gentle transition between the upper and lower parts of the room still needed a solution. Actually we knew from the very start where to find that solution. And at last we had to face up to it: a new PH luminaire had to be developed, based on an old type from the 1930s, the PH four-shade, but reconstructed on a new program. The close-up (fig. 10) demonstrates that four instead of three shades change the illumination above the suspension plane, resulting in a marked softening of the boundary between the upper and lower halves of the room (fig. ill. One can look up into the big room shadow A with much less difficulty. The room is not seen as divided but coherent, and more so than the photograph shows.

But that is not the only thing. The larger volume of the Iuminai.re and the greater diffusion of the light compared to the common PH three-shade means that the distance to the wall surface – or to free-standing objects on the floor - is less critical. It was therefore possi bIe to use only one size of luminaire and still achieve the small shadow D, type 1, on the walls.
The close-up also shows how the directly lighted inside of the luminaire gradually becomes darker, from the bottom shade to the large shade in the top. This shows that what was said previously about the D shadow, namely that it presupposes shadow type 0-1.5, is an approximation, necessary and useful, but not sufficient. It does not say anything about the possible refinement of shadow and. texture, which luminance variations within the specified solid angles can add.
The light from a PH four-shade is in fact composed of four different solid angles, each with its place on the shadow scale and each with its own luminance. Most probably, each of them is capable of dealing with a certain size of details, in the same way as the Four Shadows are size-determined. So despite all theory, there is still a need for qualified observation. II1II  

Lighting design concpets

Richard Kelly

A significant part of this task – a basic description of the various functions of light as a medium for imparting information – was developed in the fifties by Richard Kelly, a pioneer of qualitative lighting design.
Kelly describes the first and basic form of light as ambient light. This is the light that provides general illumination of our environment. It guarantees that the surrounding space, plus the objects and persons in it, are visible. This form of overall, uniform lighting ensures that we can orient ourselves and carry out general tasks. It is covered to a large extent by the ideas underlying quantitative lighting design, except that ambient light in the Kelly sense is not the aim of a lighting concept, but only a basis for further planning. The aim is not to produce overall lighting of supposedly optimum illuminance, but differentiated lighting that can be developed taking ambient light as the basic level of lighting.
To achieve differentiation, a second form of lighting is required that Kelly refers to as focal glow. This is the first instance where light becomes an active participant in conveying information. One important aspect that is taken into account here is the fact that our attention is automatically drawn towards brightly lit areas. It is therefore possible to arrange the mass of information contained in an environment via the appropriate distribution of brightness – areas containing essential information can be emphasized by accent lighting, information of secondary importance or disturbing information toned down by applying lower lighting levels. This facilitates the fast and accurate flow of information, the visual environment, with its inherent structures and the significance of the objects it contains, is easily recognised. This also applies to orientation within the space – e.g. the ability to distinguish quickly between a main entrance and a side entrance – and for the accentuation of objects, as we find in product displays or the emphasizing of the most valuable sculpture in a collection.

The third form of light, play of brilliance is a result of the realization that light not only draws our attention to information, but that it can represent information in itself. This applies above all to specular effects, such as those produced by point light sources on reflective or refractive materials; the light source itself can also be considered to be brilliant. This “play of brilliance” can lend prestigious spaces in particular life and atmosphere. The effect produced traditionally by chandeliers and candlelight can be achieved in modern-day lighting design through the purposeful application of light sculptures or the creation of brilliance from illuminated materials.

William Lam

With his differentiation between the basic functions of light Kelly made a substantial contribution towards the theory behind qualitative lighting design. He provides a systematic presentation of the means available. The question that still remains open is: according to what criteria are these means to be applied? The lighting designer is obliged to continue to depend on his own instinct, experience and the inadequate support provided by the quantitative criteria laid down in the standards when it comes to analysing the particular lighting context – determining the special features of the space, how it is utilized and the requirements of the users.
Two decades pass, however, before William M. C. Lam compiles the missing catalogue of criteria: systematic, contextrelated vocabulary for describing the requirements a lighting installation has to meet. Lam, one of the most dedicated advocates of qualitative lighting design, distinguishes between two main groups of criteria.

He first describes the group of activity needs: the needs for information related to specific conscious activities. To understand these needs it is essential to know the characteristics of the various visual tasks to be performed; analysing activity needs is therefore in line with the criteria laid down for quantitative lighting. As far as the aims of lighting design are concerned, there is general agreement on this point; the aim is to design functional lighting that will provide optimum visual conditions for the specific task – be it work, movement through a space, or leisure activities.
In contrast to the advocates of quantitative lighting design Lam objects strongly to uniform lighting aligned to the respective most difficult visual task; he proposes a far more differentiated analysis of all the activities that will take place according to location, type and frequency.
Even more important than this new evaluation of a group of criteria that already existed, is what Lam calls his second complex, which comprises biological needs. In contrast to activity needs, which are derived from man’s occupations with specific tasks, biological needs covers the psychological need for information, the more fundamental aspects of the human relation to the visual environment. Whereas activity needs arise from specific conscious activities and are aimed at the functional aspects of a visual environment, biological needs comprise mainly unconscious needs, which allow us to evaluate a situation from an emotional point of view. They are concerned with our feeling ofwellbeing in a visual environment
In his definition of biological needs Lam presumes that our attention is only dedicated to one visual task in moments of greatest concentration. Man’s visual attention is almost always extended to observe his entire surroundings. Any changes are perceived immediately, behavior can be adjusted without delay to adapt to the changed situation.
The emotional evaluation of a visual environment does not only depend on whether it provides the required information in a clear fashion or whether it withholds it from the observer – the feeling of unease that arises in confusing situations. We have all experienced the feeling of being disoriented in the mass of visual information at an airport or when looking for a specific office in a local authority building.

For Lam the first of the basic psychological needs for environmental information is the need for orientation. Orientation can be understood in this case first in a spatial sense. It refers to how well destinations and routes can be identified: the spatial location of entrances, exits and what the environment specifically offers. This may be a reception, a special office or the individual departments of a department store. But orientation also comprises information about further aspects of the environment, e.g. the time of day, the weather or what is happening around us. If this information is missing, as may be the case in closed spaces in department stores or in the corridors of large buildings, for example, we feel the environment to be unnatural and even threatening; only when we have left the building can we suddenly make up for the information deficit – we establish that it has become dark and started to rain, for example.

A second group of psychological needs is targeted at how well we can comprehend surrounding structures. It is important that all areas of the spaces are sufficiently visible. This is a decisive factor in our feeling of security in a visual environment. If there are niches and corridors we cannot see into or parts of a space are poorly lit, we feel uncomfortable and unsafe. Dark corners, e.g. in subways or dark corridors in hotels at night, may contain danger, in the same way as overlit areas.

Comprehension of our surroundings does not mean that absolutely everything has to be visible, it comprises an element of structuring, the need for a clearly structured enviroment. We feel that a situation is positive when the formand structure of the surrounding architecture is clearly recognizable, and when important areas are designed to stand out against the given background. Instead of a confusing and possibly inconsistent flow of information the space thus presents itself as a clearly structured whole.
When accentuating specific areas it is not only visual tasks that traditionally receive attention that should be underlined. A view outside or the presence of other points of interest, e.g. a work of art, can be equally effective.

A third area consists of the balance between man’s need for communication and his right to clearly defined private spaces. Both extremes, complete isolation and complete public exposure, are felt to be negative; a space should promote contact to other persons, while at the same time allowing private spaces to be defined. A private space can be created by defining an area with light: a seated area or a conference table within a large room, for example, and making it stand out from its surroundings.

Architecture and atmosphere

Both main groups of William Lam’s criteria describe man’s needs, his needs for a functional and perceptually sound environment. Besides this analysis, which is based on the needs of man as a perceiving being, it must not be forgotten that light and luminaires also make a substantial contribution towards the aesthetic effect of architectural design.When Le Corbusier describes architecture as “the correct and magnificent play of masses brought together in light”, he underlines the significance of lighting on the design of buildings.
Lam’s demand for a clearly structured visual environment comes very close to fulfilling this task, but does not cover all aspects. It is certainly possible to structure a space according to the psychological needs of the users by applying different forms of lighting. Any decision to go for one of these approaches implies a decision to create a different aesthetic effect, a different atmosphere in the space. Apart from merely considering the needs of the perceiving being it is also necessary to plan the interplay of light and architecture.

As with user-oriented lighting design, light also has a supporting function in architecture. It is a tool for rendering the given architectural structures visible, and contributes towards their planned effect. Lighting can go beyond this subordinate role and itself become an active component in the design of the space. This applies in the first place for light that is not only able to render architecture visible, but also to enhance the intended appearance. This applies primarily to luminaires and their arrangement. Luminaires can be discreetly integrated into the architecture – e.g. via recessed mounting in the ceiling. The fixture itself is not visible, it is only the light that has effect. But luminaires can also be added to architecture: in the form of a light structure, an alignment of spotlights or a light sculpture, the lighting installation itself can become an architectural element that can purposefully change the appearance of the space.  

Light-zone(s): as Concept and Tool

An architectural approach to the assessment of spatial and form-giving characteristics of daylight
Merete Madsen, The Royal Danish Academy of Fine Arts, School of Architecture, Copenhagen

Abstract

Daylight1 is essential to the experience of an architectural space. Nevertheless, amongst the handful of predominantly scientific methods available to assess daylight in architecture, there are only a few considering the spatial and form-giving characteristics of daylight.
This paper investigates light-zone(s)2 as concept and tool, which can be taken as a point of departure for a new method to perceive, consider and analyse daylight in architecture.
As concept, light-zone(s) are areas, fields or zones of light. It is a way of considering a space’s daylight as (forms of) bubbles or spheres of light, which as light-zones can be compressed, expanded, combined, exploded, etc., all according to the character of 'the meeting' between the light-zone(s) and the space itself (inclusive of the space’s content). Thus, the daylight in a space can be regarded as a composition of light-zones. As tool, light-zone(s) are (spatial) groupings of the lighting variables (intensity, direction, distribution and colour), which are significant to the space and form-giving characteristics of light. That is to say, the light-zone(s) tool is the point of departure for a method of creating a spatial ‘grasp’ on daylighting variables in a given space.
The relation between the light-zone(s) concept and tool respectively can be described as follows: On the one level lightzone(s) can be explored as an architectural idea or notion, thus belonging more to the field of architectural theory. On another more practice-driven level, light-zone(s) can be articulated and specified in relation to lighting technology.

Alvar Aalto’s Municipal library in Rovaneimi [66°N]

The distribution of daylight is fairly uneven in the lending room of Aalto’s library in Rovanimi. The varying daylight-levels mean that the space’s light-zones are defined individually and perceived as special kinds of ‘rooms within the room’ (fig. 3).
The library is ‘unusual’ in two ways: Firstly Rovaniemi is situated in northern Finland (at the polar circle), where the presence of daylight is as much an annual as a diurnal phenomenon and the twilight periods are long, varied, and rich in colours. Secondly Aalto is mainly known for a delicate treatment of an almost shadowless and soft daylight. The library in Rovaniemi is Aalto’s most ‘dramatic’ daylight composition, but still the light is perceived as soft.
The analysis of the library space’s daylight resulted in a division into three principal daylight-zones and some smaller artificial light-zones. The daylight-zones will be referred to as light-zones, where as the artificial light-zones will be defined as artificial light-zones.
The three light-zones of the lending room are as follows: One light-zone is created around a central control desk; a series of similar light-zones are created around a row of reading niches along the northern fanshaped wall; and finally one light-zone is created by four conical skylights above a reading area between the control desk and the back entry (Fig. 4). This paper will focus on the two first mentioned light-zones and only take the last one into account in relation to the lending room’s overall composition of light-zones.
Each of these light-zones relates to a particular function of the lending room. The functions are transformed into an almost ritualistic sequence in which one finds a book (the reading niche’s illuminated bookshelves), browses through the book on various levels (the reading niches lightzones), and then borrows the book (the control desk’s light-zone). One moves in the transitional shadow-zone.
One enters the lending room toward the control desk’s light-zone. Apart from providing a good sense of daylight in the innermost part of the space, the control desk’s light-zone accentuates the desk area as the room’s centre of circulation. The control desk’s light-zone is rather intense, because the direct daylighting is supplemented by reflected sunlight as well as daylighting that is indirectly reflected downward onto the vertical surfaces of the columns.
From the control desk one sees the entire room. At the same time one can clearly perceive the space’s light-zones (as ’rooms within the room’). The effect of such individually marked light-zones has most precisely been described by Henry Plummer, who writes: “When a vivid light is encompassed by space it acts as a magnetic centre or node, and when seen in the distance establishes a magnetic axis, the former exerting a centripetal and the later a lineal gravity”11. The function of the intermediate shadow-zones, which limits and defines the light-zones, is thus circulation.
The reading niches along the north wall are illuminated by the ‘skylight-scoops’12 that follow the wall’s fan-shaped form. These apertures are a hybrid between a clerestory window and a skylight: ‘skylight scoops’. The skylight scoops act as ‘eyebrows’13, preventing a direct view to the segment of the sky that could cause glare when seen from the shadow-zone. At the same time, the reading niche’s light-zones are intensified because the scoops reflect the daylight downwards into the reading niches and onto the vertical surfaces of the bookshelves (Fig. 4, top drawing), which to a high extent define the light-zones. The light-zones defining the north-facing reading niches have the added refinement of connecting the sunken reading niches with the library’s upper level. In other words, the composition of light-zones, as well as a single light-zone, is able to both divide the space as well as to connect different spaces.
In the reading niches, the daylighting is augmented by the bookshelves artificial lighting and by a row of fixed desk lamps in the sunken reading niches, which create warm ‘light-caves’. The combination of the cool daylight-zone, enveloping zones of warmer artificial light, are rich in character – especially at this northern latitude, where the periods of twilight are long and varied. In front of the control desk, Aalto created an artificial light-zone, where the meeting between the patron and the librarian is embodied in a meting between a daylightzone and an artificial light-zone. The lending room’s precise daylighting composition makes particular demands on the artificial lighting, which is either situated within the daylight-zones or inside the transitional shadow-zone. Artificial light is not positioned in the area between light and shadow, where it would eliminate the daylighting composition and the experience of lightzones. The composition of light-zones in the Rovaniemi library’s lending room is thus an example of a space where different lightzones are defined individually. Together the light-zones (and the shadow-zone) create an overall composition, where the light-zones hold the ‘functions’ of the space and the transitional shadow-zones limits and define the light-zones. The ‘de-energised’ shadowzone creates a spatial ‘pause’ between lightzones.

Le Corbusier’s foyer in Paris [49°N]

The foyer in Le Corbusier’s own apartment in Paris has been chosen because of the complex composition of light and space. The objective of this analysis is to examine the light-zone(s) concept and tool in relation to a case where multiple light-zones merge, and with that challenge possible limitation of the light-zone(s) concept and tool.
Le Corbusier’s apartment consists of three main parts: the atelier towards the east, the dwelling area towards the west, and a top storey with a guest studio and roof garden. The foyer serves as the central link between these three parts (Fig. 5).
One enters the foyer next to a sculptural stairway opposite a blue wall with a long horizontal window. Two large pivoted doors lead from the foyer to the dwelling area and the atelier. The wall and the pivoted door towards the dwelling area are dark brown, as is the back of the door to the atelier. The tiles on the floor are sand-coloured. The rest of the space’s surfaces are white, with the exception of the steps that have a dark greybluish hue.
At first, the foyer’s daylight is perceived as one (fairly uniform) entity of light. That impression can be confirmed by daylight measurements on a horizontal level. However, the space, and in particular the stairway, clearly imply a composition of light and shade.
When analysing the space on the basis of light-zone(s), one can divide the foyers daylight into two principal light-zones: one is created by the long horizontal window, placed at the top of the blue wall; the other is created by a glass pavilion on the top floor (Fig. 6).
The light-zone of the horizontal window illuminates the entire space except the ceiling, the blue wall, the floor area just in front of the blue wall and the risers in the lower part of the staircase.
The light-zone created by the roof pavilion also illuminate most of the space except the ceiling and the upper part of the walls, the staircase’s cylindrical base and the risers in the lower part of the staircase.
As a result, the form-giving characteristics of light and shade of the staircase are as follows: the risers are divided into a darker base and a brighter top because the top risers are illuminated by both light-zones, whereas the base risers only receive reflected light from the surfaces of the space. The treads are uniformly lit, mainly by the roof pavilion’s light-zone, yet with an evenly decreasing luminance downwards. Finally, the cylindrical base is illuminated from the horizontal window’s light-zone, where the main lighting direction is perpendicular to the staircase and thus makes the base’s form stand out by means of it being shaded because of its curvature (cosine low).
This composition of space, staircase, and merged light-zones has consequences for the way one moves, as well as the way space and staircase are visually perceived.
The movement can be divided into two axes: a horizontal movement between atelier and dwelling area, and a vertical movement from the foyer to the roof (garden). The horizontal movement is motivated by the light-zones of the horizons towards east and west, while the vertical movement is motivated by the roof pavilion’s light-zone from above. The vertical movement varies as one ascends and descends the stairs. The way up is experienced longer than the actual amount of steps one takes, because it is divided into a darker base (that one leaves) and a brighter top (to which one rises). The descent is ‘difficult’ and slow, as one is ’washed’ down the steps towards ‘darkness’ by the intense light-zone of the roof pavilion. This is emphasized by the fan-shaped sequence of the evenly lit treads which are ‘tricky’ to distinguish. Of course, the ‘lack’ of an outer banister doesn’t make it quicker. Descending the stairs makes one utterly aware of the bodily movement, an awareness that is an important part of the perception of the foyer. Even though the roof pavilion’s light-zone makes the vertical axis prominent, the actual physical movement is not straightforward, because the base of the staircase (as one’s starting point) is ‘hidden away’ in the shade.
The ‘light-zone of the horizon’, which constitutes the horizontal movement, generally has a profane meaning, representing everyday life and rituals. The vertical movement is motivated by the predominantly vertical flow of light from the roof pavilion. A vertical daylighting direction constituting the ‘light-zone of the the sky’ generally holds a sacred meaning, in this case representing the rising from the foyer’s relative dimness to the full daylight and 360° panorama of the roof garden, that Le Corbusier called his ‘meditation space’14.
The visual perception of the foyer is equally as refined. Le Corbusier has described his foyer as the origin for his notion of l’espace indicible. More specifically, it was his experience of the foyer with one of his own paintings hanging on the northern wall (at a particular occasion)15. I choose to believe that the painting can also be a methodology to see. Le Corbusier can presumably be called a cubist painter. One of the ‘effects’ of cubism is to represent objects simultaneously from multiple viewpoints, in order to create a perception of ‘a/the fourth dimension’. The three-dimensional staircase can be seen in a similar way in reverse. One can see the composition of light and matter as plan, section, and elevation at one glance: The fan-shaped sequence of evenly lit threads as plan; the division of risers as section; and the cylindrical base, with its form-giving shading, as elevation. Such ‘effects’ are only part of the vivid composition of light, space, and colours. Another is that the top and base of the staircase can, when seen from the atelier, change positions because the brighter top of the staircase seems to advance in space while the darker base perceptually ‘diminishes’ and ‘moves’ further away. Thus, the three-dimensional space can turn twodimensional or relate to other dimensions. However, the foyer’s composition can’t be observed from one viewpoint only. The experience of the space accumulates as one moves into and through the foyer.
As opposed to the form-giving effects of the merging light-zones on the staircase, the distribution of light on the walls of the foyer is fairly uniform. Here, the lack of form-giving shadows on the wall surfaces emphasizes the colours. It’s perceived somewhat like the coloured wall surfaces ‘dismantles’ and are perceived as purely geometrical figures ‘floating’ in space according to the perspectives of colours.
The spatial and form-giving characteristics of daylight in Le Corbusier’s foyer seem inexhaustible. In relations to the lightzone(s) concept and tool it would be fair to conclude that the merging of light-zones holds a potential to give form to compound objects like the staircase.
This study of Le Corbusiers foyer confirms the thesis that light-zone(s) motivate movement (locomotion) in space. Despite the fact that the foyer’s daylight can be analysed as two principal light-zones, the daylight of the foyer acts as a shadow-zone in relation to the light-zones of the dwelling area, atelier, and roof pavilion. This also shows that the light-zone(s) concept is malleable. With reference to the discussion about light-zone(s) vs. darkness-zone(s), the perception of light-zone(s) always depends on adjacent light-zone(s).