LUMINOUS ELEMENTS

Thus far we have examined visible characteristics of lighting in terms of how lighting interacts with and reveals the surfaces and the objects within the room. Inevitably, luminaires have some impact on the appearance of the space. We can see many examples where the designers have sought to minimize that impact by concealing the lamps and building the luminaires into architectural details. These can take many forms: cornices to provide uplighting onto the ceiling; stepped ceiling perimeters to enable wallwashing; or low-brightness luminaires recessed flush with the ceiling. In all these cases the designers are expressing the wish to have illumination without luminaires.

Luminaires as design elements

There are alternative design approaches. When the Sun King, Louis XIV, had the Hall of Mirrors at the Palace of Versailles illuminated with one thousand candles, this spectacular vision was celebrated by having the candles mounted on glittering crystal chandeliers. When gas engineers introduced the next wave of illumination technology, it was popular to illuminate the parlour with a gasolier, being an elaborate multi-arm chandelier based on earlier cast metal candleabra. Derivative forms of decorative luminaires remain popular for domestic lighting, but also newer forms of ‘architec- tural’ luminaires are often used in commercial and recreational buildings. The renovated luminaires in the Philadelphia railway station shown in Plate 9 are switched on all day even though the daylight streaming in through the windows provides perfectly adequate illumination. These are planned elements in the design concept which are intended to be seen, but this raises a potential conflict. We have seen how the phototropic effect draws attention to the brightest elements in the field of view, so is the aim to reveal the space and its contents, or to display the lighting equip- ment?

There is a conundrum that is familiar to lighting practitioners: ‘One man’s sparkle is another man’s glare.’ The glittering chande- liers in a theatre foyer may be a source of irritation and discomfort to the clerk who sits at the ticket counter, so why does the management not install comfortable, low-brightness luminaires instead? The answer is that ‘the bright lights’ impart a festive atmosphere in this setting that sets the mood of the theatregoers and raises their sense of excitement. These visitors need to be able to read the seat numbers on their tickets, but this is not a sustained task and they can achieve this while they pass through

the space without sensing discomfort. Their responses mean more to the management than those of the poor ticket clerk, who has to learn to cope or seek a more comfortable occupation.

The shopping centre in Kowloon, Hong Kong, shown in Plate 10 has a lively and vibrant atmosphere. The brightness and sparkle of the unshielded luminaires is multiplied by reflections from an elabo- rate stainless steel sculpture that hangs through almost the entire height of the atrium. Luminaire brightness has been employed as a vital design element.

Luminaire brightness may become a real concern in workplaces, and here the factors that disturb the ticket clerk cannot be overlooked. Attention has focused onto the needs of office workers, and in particular, on the avoidance of bright reflected images of luminaires in computer screens. This concentration onto a single aspect has had unfortunate consequences, and has led to many dismally unattractive workplaces in which closely spaced, fully recessed luminaires concentrate their light output vertically downwards. Such lighting undoubtedly avoids bright images reflected in the computer screens, in fact the brightness of the luminaires can be so low that it may be difficult to see whether the luminaires are switched on. Nonetheless, the harshness of the illumination attracts criticism. The vector/scalar ratio is high, and the appearance of strongly directional lighting streaming downwards from a dark ceiling has been described as the ‘cave effect’. Perhaps the most surprising aspect of this form of lighting has been the vast number of office workers who have been subjected to its unpleasantness, as it has continued to be installed as the solution to the electronic office despite ample evidence to the contrary. At any rate, it has demonstrated that to design light- ing with the single-minded aim of making the luminaires almost invisible can lead to very unsatisfactory results.

Discomfort glare

In Section 2.2 we discussed disability glare, which occurs when the visibility of detail to be seen is reduced by scattered light within the eye from bright elements within the field of view, such as luminaires. There is another form of glare that is associated with the presence of bright luminaires in workplaces, and it is termed discomfort glare. There may be no noticeable loss of visibility, in fact, the effects of discomfort glare may not be apparent until after a prolonged period of exposure. It is for this reason that it is partic- ularly associated with workplaces in which workers have to maintain fixed viewing directions for long periods, and the symptoms are headaches, eyestrain, and fatigue. There are

substantial interpersonal differences in susceptibility to discomfort glare.

Discomfort glare has been the subject of several research inves- tigations. It has been found that subjective assessments of discomfort glare increase with the luminance of the glare source and its apparent size, and reduce with the ambient light level and the angle of separation between the glare source and the direction of view. Within certain limits, the effect of multiple glare sources is additive. There have been several attempts to devise discomfort glare rating systems, so that complete lighting installations can be assessed at the design stage, and a predicted value can be compared with a scale of limiting values related to various activi- ties and viewing conditions. The Unified Glare Rating is probably the most widely used rating system, and while designers may encounter limiting UGR values being prescribed for some specific situations, this is more a way of users seeking to avoid exposing their workers to unsatisfactory lighting rather than a useful tool to enable a committed lighting designer to devise an installation that is well suited to the situation. It is important that a lighting designer is alert to the difficulties encountered by some people in coping with sustained and visually demanding work, but it is generally more productive to devise ways of avoiding the causes of discom- fort rather than seeking to evaluate how much discomfort glare will be present. It may be added that studies comparing glare ratings with subjective assessments generally show poor correlation.

Luminaires and lighting design criteria

We have discussed the illumination hierarchy, for which the light- ing designer makes decisions on how to employ local variations of illumination to attract attention and express differences of empha- sis. In making these decisions, the appearance of luminaires may be given little attention and it is assumed that they will, as far as possible, be concealed. Even where a source of light is a focus of attention, such as an altar light or the Eternal Flame, this is unlikely to be a significant source of illumination and the lighting designer’s concern is to ensure that the appearance of the surrounding surfaces does not detract. Bright or otherwise conspicuous luminaires would tend to upset the planned effect of the illumina- tion hierarchy.

We have also examined what is meant by the sharpness of light- ing, and how this relates to the angular size of the luminaire and the highlight ratio. Consider a retail display of glassware. We have already seen how the appearance of glassware has almost nothing to do with illumination (Figure 2.32), and the appropriate strategy

for lighting involves the use of compact, high-luminance light sources which do not need to be mounted close to glassware. Should these sources be concealed? The highlights associated with the glassware are informative, revealing the forms, smooth- ness of surface, and the lustre of merchandise. The luminance of the lamps will inevitably be higher than the luminance of the highlights, and even though their brightness does not impart infor- mation about the glassware, it may add more sparkle to the scene and to the eye-catching qualities of a display. It is unavoidably a judgement call, and one that a lighting designer has to consider. After all, why does a formally laid out dinner table appear so entrancing when the crockery, cutlery and glassware are illumi- nated by candlelight? And who would want to conceal the candle flames?

To quote J.M. Waldram (1976) again, ‘If there’s nothing worth looking at, there’s nothing worth lighting.’ Well, it sometimes happens that a designer is confronted with a situation that needs lighting and in which there is little or nothing worth looking at. To flood the space with light can do no more than reveal its bland- ness. This can be a situation in which the luminaires become the things worth looking at. Generally, this book has addressed situa- tions where the designer’s objective is to bring electric lighting to spaces that have been designed by someone else, and the aim is to support the design objectives of the principal designer. A designer who steps beyond that role and undertakes to select or design luminous elements to be added to a space is moving into the realm of interior design, and there are many ways in which luminaires can become a vital part of the scene. The solution may be quite simple. Plate 11 shows a market café close to the water- front in Stockholm. The luminaires express the nautical location; they add sharpness to the lighting; and they radiate a glowing warmth. Some of these aspects fall outside the scope of this book.

There are many ways of measuring lighting. The ones that matter to a lighting designer are those that relate to the observation-based experience of lighting. It is for this reason that readers are encour- aged to accompany observation with measurement.

The two sections in this chapter deal with illuminance-based and luminance-based measurements. In both cases, light is evaluated according to the photopic-adapted visual response (see Appendix A1) which ignores colour. It is possible to obtain a chroma-meter, which is an advanced type of illuminance meter that gives readings of illuminance, chromaticity and correlated colour temperature, but usually designers rely on colour data given by lamp manufacturers. There are no portable meters that measure colour rendering.