Old, New, Dark, Blue - The Art of Lighting of Footbridges

July 17 2014 — by Mark Major
Education | Inspiration
Like the design and engineering of bridges, lighting design is both an art and a science; it aims to provide a creative solution to what is often perceived as a technical problem. In so far that any footbridge needs the application of artificial light during the hours of darkness, its illumination must be carefully considered. This is not only to meet the requirements for safety, security and accessibility but also to ensure that its form is properly revealed. There are also the considerations of the impact that any lighting equipment may have on the appearance of the bridge by day, access for maintenance, potential environmental impacts such as light pollution, capital and running costs – the list goes on. A successful lighting scheme might therefore be seen as one that successfully balances a number of design constraints to achieve an optimum solution. At the same time it is often the case that the very best designs also possess a little bit of ‘magic’ that help elevate the project to become a special experience - not only for the people using the bridge but also those viewing it from afar. This article briefly looks at the background, approach and key design criteria that are required to be considered when illuminating footbridges. It also touches on the way that changes in technology are allowing much greater integration of the lighting into the design of footbridges as long as provision is made for the light early within the design process. Finally it looked at some examples of how lighting has been applied through four cases studies – old, new, dark and blue.
1. Introduction
This paper seeks to outline an approach to the lighting of footbridges that goes well beyond the idea that their illumination is simply about ensuring that people can cross them safely after dark. That basic requirement is a given; the idea that light is needed to provide safe passage is an extension of the principles that apply to the provision of all public lighting within the built environment. In so far that a footbridge connects one route to another the requirement appears simple: if the paths either side of a footbridge are lit then the footbridge itself should also be illuminated to provide continuity. How that light is provided, its quality, quantity and effect and the key drivers and requirements for the design are all considerations that contribute toward the delivery of an appropriate solution. Whilst in some cases the provision of what might be termed ‘functional’ lighting to the route is sufficient it is increasingly common to find that an additional layer of light is desirable – one that serves to enhance the character of the bridge, create an identity and provide visual expression. Whilst this ‘aesthetic’ lighting may be regarded as ephemeral the value that it adds is considerable. After all, if great efforts are made to create an appealing appearance for a footbridge by day why should it not be similarly appreciated after dark?

In this paper I will be seeking to examine the background to lighting on footbridges, the approach that might be taken to their illumination, the various issues that need to be addressed and the way that technology is shaping our thinking. This will largely be done with reference to the work of our practice, Speirs + Major which has been responsible for the illumination of a large number of footbridges in the last two decades. To that end this paper must be seen as a first-hand account of lighting in practice rather than an academic text that draws upon a multitude of external references and sources.

2. Background
Looking to the past in the field of architecture and engineering can often provide clues not only as to the way to address the design problems of the present but also how things might develop in the future. This article therefore begins with a brief look at the development of the lighting of footbridges.

There is little evidence about the manner in which footbridges were lit until the evolution of industrialised light – first through gas and then electricity. That is not to say that there was no illumination prior to that point, undoubtedly there would have been some light provided in some way. Most likely however it would have been a reflection of the manner in which the adjacencies were treated through ad hoc arrangements of burning torcheres, oil or candle lanterns etc. It should also be remembered that prior to the organisation of public lighting systems people frequently carried their own illumination in the form of portable torches or were guided by servants or hired hands who carried torches before them.

Whilst organised street lighting had existed in European cities since the 15th century it was only at the beginning of the 19th century that regulated and maintained systems of public lighting began to appear more universally. This was initially through the introduction of gas lighting to major streets and thoroughfares. It is recorded that gas was used to illuminate major bridges as well as streets; by example following the successful introduction of the first gas lighting scheme to Pall Mall, London in January 1807 by William Murdoch, Westminster Bridge was lit in the same manner on 31st December 1813. Illustrations of the time show that the lighting of bridges was typically provided by clusters of glowing decorative lanterns placed along the line of the outer balustrade on either side of the bridge. The positions of such groups were often related to the architectural design rather than the need to achieve a consistent effect. The light provided by many of these arrangements would therefore have been patchy in the extreme when compared to the more uniform solutions of today.

Whilst such schemes provided light to both the thresholds of the bridge as well as the route across they also served to signal the crossing when seen from a distance. This provided some visual emphasis. Contemporary paintings of the time by artists such as Whistler and Turner make much of the effect created by such lanterns either seen through the mist or reflected in the water. In considering such solutions it can at least be seen that the early lighting of bridges, including footbridges, was both functional and aesthetic at the same time – and what is more ‘integrated’ with the architectural idea.

With the wider electrification of public lighting at end of the 19th century came a change: Whilst once again the lighting of routes across bridges generally followed the municipal standards that related to the provision of safety and security such schemes were often delivered through standardised sources and luminaires rather than employing purpose made and integrated architectural solutions. To that end, and in particular from the 1950’s onwards, many bridges found themselves being fitted with what might be considered as more utilitarian amenity lighting that solely met the basic requirement for lighting the deck. Such schemes often included arrays of electric lanterns or bulkheads mounted on simple street columns or brackets. These frequently used efficient but poorer quality light such as low pressure sodium lamps, mercury or fluorescent due to the relatively short life of other alternatives such as tungsten halogen. Whilst providing continuity with the local street lighting the character of such solutions often did little to enhance the appearance of the structure either by day or by night.

Notwithstanding this, the idea that bridges might receive additional decorative lighting found favour with floodlighting schemes being employed to illuminate the overall form or key parts of bridges such as arches, towers, cable stays, etc. Even existing historic bridges that had never previously been lit began to have cosmetic lighting treatments added to them as part of a perceived need for ‘beautification’. Such initiatives were often driven by local town halls with the encouragement of lighting manufacturers who sometimes even offered commercial incentives such as free or subsidised design. A good example of this was the floodlighting of Tower Bridge in London by Philips Lighting in the late 1980’s which was recently replaced by an updated scheme sponsored by GE in 2012 as part of the Olympic legacy.

Having said that, a large number of celebrated schemes for bridges have been designed by independent lighting designers across the world, including Motoko Ishii’s 1989 scheme for the Yokohama Bay Bridge, Yann Kersale’s influential lighting design in 1994 for the Ponte Du Normandie and Lighting Design Partnership’s award-winning lighting scheme for Ben Van Berkel’s Erasmus Bridge in Rotterdam in 1996 to name but a few.

The last twenty years however has seen progress being made, particularly with respect to footbridges, where the designer of the bridge has worked in close collaboration with a lighting designer or illumination engineer with the view to seeking ever more imaginative approaches to lighting, either through a return to solutions that are carefully customised as part of the architecture of the bridge or integrated to such an extent that the bridge itself appears to produce the light from within. Examples include the ground breaking LED lighting scheme in 1999 for a footbridge in Duisberg by LDE Belzner Holmes to the epic scale of the recently completed Margaret Hunt Bridge in Dallas by Santiago Calatrava. Our own practice Speirs + Major has designed a number of such solutions to footbridges over the last two decades including The Golden Jubilee Bridges, London, Gateshead Millennium Bridge, Infinity Bridge, Stockton-On-Tees and the Twin Sails Bridge in Poole.

3. Approach
Having briefly looked to the past the next part of this article examines an approach that may be taken to the lighting of footbridges. Like all methodologies it should not be seen as a guaranteed recipe for success, rather as a guide.

The starting point for lighting footbridges is always to ask the following: ‘Does the bridge need lighting - and if so why?’ In some cases the answer to this question is ‘no’. Such an answer certainly applies to structures which sit within an unlit context such as a sensitive natural or historic environment. It would generally be the recommendation in such settings that a footbridge remains in darkness to harmonise with its surroundings. Of course there are always exceptions to this rule and this paper looks at one such example as a case study: the Sackler Crossing at the Royal Botanic Gardens, Kew. In many other cases however the answer to this question is ‘yes’ in so far that the paths leading to and away from the footbridge are illuminated which in turn creates the need to light the bridge deck as a minimum to preserve the continuity of the lit route.

As well as lighting the route it might also be considered appropriate to provide additional lighting to help create an identity for the structure after dark. This could be to reinforce its presence as a landmark, celebrate its design, reveal its form – or all of these reasons and more.

Given this we can see that the proper illumination of any footbridge may reasonably consist of at least two distinct ‘layers’ of light:

The first of these may be regarded as ‘functional’ in so far that it provides the means by which people can cross safely from one side of the bridge to the other. The second is ‘architectural’ in that the role of the light is to reveal the form and surface materiality of the bridge. Both of these layers of light should be regarded as ‘aesthetic’ in that they actively contribute to the appearance, character and identity of the bridge at night. What is more the correct balance between these two must be achieved in a manner whereby any solution is fully integrated into the overall design rather than being merely cosmetic.

Beyond the idea of ‘layers’, one can also consider how the different ‘elements’ of a footbridge might be treated. Whilst every project is different most footbridges consist of common features such as the bridge deck and its soffit, the balustrade and handrail system, the principle structural support, thresholds where the bridge meets the land, points of access such as stairs and ramps where applicable, and so on. When approaching the lighting design it is often prudent to consider each of these elements individually as to whether they are required to be lit – or at least to provide support for lighting equipment. In some cases certain elements will remain unlit, in other cases the manner they are revealed after dark will be the inverse of the way they are seen by day. In certain circumstances lighting a specific element might be desirable but the technical complexity of doing so might prove extremely challenging. A good example of the latter is the arch of the Infinity Bridge at Stockton-on-Tees which features as a case study latter in this paper. The arch itself was so significant to the image of the bridge itself and the idea behind it that it was essential to express it after dark. At the same time the challenge of lighting a continuous structural form of that nature and without creating excessive light pollution presented a real challenge that created the need to locate the various spotlights required in specific positions and then to and provide safe access for their maintenance.

Having considered the form of the bridge through ‘layers’ and ‘elements’, the next key factor is the requirement for the light itself. This can be determined in terms of quality, quantity and effect.

Whilst there is no specific established means by which the quality of light may be measured it can generally be considered in terms of its ‘colour appearance’- how warm or cool it appears and ‘colour rendering’ - its ability to accurately reveal colour. These two factors are largely dictated by the choice of source which we will look at later in this article. What it is important to note however is that the chosen quality of light can influence the quantity of light used. Visual acuity can be much improved in relatively low levels of light by using fuller spectrum light sources and to that end source selection itself can greatly influence how much light is needed.

The best means of establishing the desired quality of the light is through sampling different sources, particularly in relationship to the colour and finish of the materials to be used. Whilst for many the qualities of light produced by different lamps such as sodium, metal halide and fluorescent are familiar the degree of variability in terms of both colour temperature and colour rendering can be so great that there is no substitute for witnessing the light. If a parallel were taken to the selection of a paint colour whilst we may decide that something is ‘red’, given the wide variety of ‘reds’ available a final selection can often only been made by looking at a swatch or sample. Selecting light is really no different in this respect.

Whilst the quantity of light required for the functional lighting will be very much dictated by the standards required of the route across the bridge the amount of light needed for the any architectural lighting is very much a matter of judgement. Whilst the former is generally measured in terms of the amount of the light falling horizontally on the bridge deck or provided vertically onto the faces of people (illuminance) the latter is better considered in terms of the perceived visual brightness of the lit surface (luminance). Whilst each of these aspects can be calculated and modelled in software the reality is that such a wide number of variables exist in terms of background illumination, degrees of reflectance and inter-reflectance of materials and finishes, that such predications may only be considered to be approximate.

What is also important to consider alongside the type and intensity of the light is the effect it will produce. Whilst lighting has the ability to enhance it can also do the opposite. This can be best understood by considering a person being lit by a single light source such as a torch. If the torch is held some distance away from the face straight on their character may be clearly and quite naturally revealed. Too much top-light and the eye sockets become dark and exaggerated with long shadows being created by the nose. Extreme side-light can create drama but only reveals one side of a personality. Put the source under the chin and a highly dramatic result occurs that completely changes your perception of the person. To that end the desired effect and degree of drama of any architectural lighting scheme for a bridge must be very carefully considered as part of the initial conception such that the final outcome and appearance of the lit form is clearly understood. Again, whilst this can be modelled as part of the design process the best way to understand the effect that will be achieved is through physical mock-ups, models and site trials.

Assuming an approach to lighting through the understanding of layers, elements, quality, quantity and effect is only one methodology for designing lighting. Either way the best lighting schemes for bridges also contain some special, undefinable ingredient – a bold idea, a visual narrative or an unusual interpretation. Certainly many of the most successful footbridge lighting solutions of recent years have something special about them that goes beyond a pragmatic or formulaic approach. This is where the ‘art of lighting’ resides – in the way in which the lighting designer might collaborate not only to evolve a solution that is specific to the project but more importantly create a memorable response. Whilst in some cases that requires ‘fireworks’ – a dynamic and bold approach, in many others such structures benefit from a sensitive, considered and more subtle approach.

4. Considerations
Having established an approach to the lighting of footbridges a number of issues are required to be considered that may act as drivers for the lighting design. As has previously been indicated lighting design, like so many other aspects of environmental design, often calls for the right balance to be struck between many conflicting requirements. Experience dictates that the following might be regarded as the key issues to consider:

4.1 Security
The primary function of any lighting scheme for a footbridge is to allow people to securely cross from one side to the other. It is well established that whilst lighting cannot prevent crime it can certainly deter it. Most importantly however it can provide people with the confidence to use a route. This is particularly important in respect of footbridges as the feeling can exist that once you have embarked upon the crossing that you may be in a position of being effectively ‘trapped’ in the event that something untoward occurs. To that end the key factor to be addressed is recognition – the ability to clearly see whether anyone else on the footbridge, and particularly someone approaching you, is a potential threat. The other is ‘perception’ i.e. the feeling that the bridge is well lit and safe. It is important to understand that confidence is created in public space after dark as much by the way in which the environment is lit as the actual amount of light used. On a footpath this is generally achieved by ensuring that there is a reasonably uniform distribution of vertical lighting that clearly reveals people – and in particular their faces. Ensuring that this happens on a footbridge is more difficult: a footpath can be illuminated by column mounted lanterns which can be made to distribute the light from above head height to achieve the desired standard. On a footbridge the use of columns is often undesirable for either aesthetic or environmental reasons - or both. To that end the proper lighting of the bridge deck, and in particular achieving the necessary vertical illuminance is often the primary technical challenge. As will be seen from the case studies that follow there are a number of techniques that can be employed other than column mounted solutions such as lighting from the handrails or the balustrade though any attempt at illumination that is below head height presents real issues with achieving sufficient illumination on faces. As a result there is often a reliance on reflected light, which in turn can influence decisions about the choice of the material and its colour for the bridge deck itself. A final point that should be made is that the adopted lighting standard for the illumination of the bridge deck must be carefully considered. It does not necessarily follow that ‘well lit’ means ‘brightly lit’ – indeed lighting that is too bright can make the eye adapt such that the surroundings become darker by contrast, especially at the thresholds. Quite often it is assumed that the lighting will simply be an extension of the lighting standard for the footways either side of the crossing. In many cases this is indeed the right standard to adopt though depending on the context making the footbridge slightly brighter can improve the perception of personal security as long as this doesn’t lead to problems of contrast. In other cases however it might be more appropriate to lower the level of lighting to respond to specific environmental requirements. Certainly where a bridge is crossing a naturally dark area such as a river it is often possible to greatly reduce the amount of light being used given the lack of competition.

4.2 Safety
The role of lighting in supporting safety on any footbridge ranks alongside security. Changes of level such as steps and ramps, lifts, thresholds and other potential hazards are all required to be positively illuminated. This often needs additional lighting to be provided at such points, but not so as to create excessive contrast, glare or other visual problems. The best solutions are those that carefully integrate lighting equipment at precisely the location required rather than general lighting being used e.g. lighting in the risers or the stringers of steps, downlighting in the architraves of lift doorways, etc. Other safety issues that must be considered relate to the context of the footbridge i.e. whether it is crossing a road, railway, waterway or has adjacency to an airfield. The lighting must be carefully considered in such cases such as not to cause a hazard to third parties. Examples include the use of coloured lighting that may be easily confused with signalling, glare that might distract drivers, upward light that may dazzle pilots and so on. The requirement for navigation lighting also needs to be considered. Whilst the structure of footbridges is often too low for aviation lighting the need to mount strobes or navigation lights for crossings over navigable waterways is a key design consideration that can often be overlooked in the early stages of designing a project.

4.3 Identity
There is often the desire to create an image for a bridge after dark that is not simply an expression of the lighting designed for security and safety. This recognises that the carefully considered composition of form and materials that is appreciated by day is often lost at night – or even on dark winter’s afternoons. Adding aesthetic illumination to create a specific identity can also often allow an element of re-interpretation and expression which reveals aspects of the bridge design that may not immediately be apparent during daylight hours. Whilst such lighting needs to be carefully considered in terms of capital and running cost, energy use, environmental impact, etc., where successful it can elevate the appreciation of the footbridge to new levels. Lighting provides a real creative opportunity not only to express the form and materiality but also to provide new interpretations thereby allowing the footbridge to be seen in a way that is simply not possible by day. This might be to illuminate different architectural elements such as pylons, cable stays, the soffit or supports to provide clarity and emphasis to the structural and architectural ideas. In other cases there might be the desire to simply illuminate the bridge in a sculptural manner as a whole. Lighting can also provide the opportunity to create a visual narrative adding dynamism and excitement to the project. This could include changing the lighting on an opening bridge to respond to its movement or relating the pattern and control of the lighting to relevant external influences such as tidal flow, wind speed or the like.

There are two primary considerations in terms of view: The view of the footbridge from a distance, and the view from the footbridge itself. In respect of the first this may be addressed by creating a lit identity as is outlined above though consideration should be given to the mid and near view and not just the way the bridge looks from a distance. In the case of the second, care needs to be taken such that the lighting does not compromise the appreciation of the context. Crossing any footbridge is often a special experience whether it is over a river, stream or some key topographical feature or across a road or railway. In all cases the view from the bridge is critical to the user’s experience. The view from a footbridge after dark can often be extremely different from that by day and to that end the lighting needs to ensure that extremes of contrast or even glare does not detract. This can generally be achieved by ensuring that the majority of the lighting is kept below eye level – that and by ensuring that the bridge does not become overlit. Other considerations might be that the context itself might be illuminated, either that or consideration is given to reflections in water or the lighting of landscape below the bridge or local to the thresholds.

4.5 Flexibility
Whilst the lighting to a footbridge rarely needs to be that flexible it is increasingly the case that both the level of illumination required and the extent to which any architectural lighting needs to be retained all night can be carefully managed through the use of lighting control. In some cases this might simply mean switching off certain non-essential lighting elements at an agreed time with the view to saving energy. In other cases it may be that the functional lighting itself is also dimmed or also turned off and then only activated by presence detection. Not only can such techniques save energy and reduce maintenance but more importantly can help reduce unwanted environmental impacts.

4.6 Accessibility
Recent years has seen the ability for those with special needs to have good access to public facilities become a fundamental and integrated part of design. The measures employed to meet the requirements for safety such as positive lighting to changes of level and thresholds go a long way to improving accessibility, though one group in particular that must be carefully considered are those with visual impairments. Whilst it is widely acknowledged that the degree of impairment varies greatly from person to person it is generally agreed that the avoidance of excessive contrast and glare are key. The latter is of particular importance as quite often the bridge design itself can mean that light sources are at low level or even set into the deck, or adjacent to the deck providing upward light. In such cases it is imperative that where such techniques are used that there are well shielded and carefully controlled so as to avoid any problems. Alongside the light itself the creative use of passive materials such as reflectors can also assist with way-finding. In some cases this can be the provision of contrasting materials on steps or the use of coloured markers to identify potential trip hazards such as are often unavoidable with bridges that are required to split or move.

4.7 Sustainability
Lighting is increasingly regarded as a social and economic tool. Not only can it bring people together and enhance their experience and enjoyment of public space but it can also create a positive benefit to the life of any city or town after dark. To that end the illumination of a footbridge might be viewed as an opportunity to make a contribution to the townscape after dark. At the same time light is a very visible form of energy use that creates unwanted environmental impacts. These include the use of energy which in turn depletes fossil fuels, the cost to the earth of embodied energy contained within lamps and lighting equipment and the issue of their disposal at end of life. Light pollution and over-illumination is also of concern. Upward light, if not carefully considered and properly directed, can make an active contribution to the sky glow that conceals our view of the stars. Alongside this unwanted artificial lighting can also impact on local bio-diversity such as bird, bat, fish and insect populations all of which can be adversely effected. To that end the artificial lighting must be used with great care; the amount of light must be properly considered and wherever possible shields, louvres and lenses ensure that it is properly directed to fall only where it is required.

4.7 Integration
Lighting can often be considered as a highly ephemeral and cosmetic exercise and as with the lighting of architecture there is a long history of lighting schemes being conceived as an afterthought or applied layer. Such solutions often result in the lighting feeling like’ ‘make up’ with the consequence that the equipment and electrical infrastructure that produce the scheme are also applied in an unsightly manner. Whilst exposed equipment may be unavoidable when lighting an existing structure such as a historic bridge, though even there every effort should be made to conceal the equipment and cabling as far as is practically possible, in respect of a new footbridge is perhaps unforgivable if the lighting solution is not properly integrated into the overall design from the start. To do this the idea of lighting the bridge and the realisation of the technical solution needs to be developed in parallel with the design of the structure itself. This in turn requires the lighting designer or engineer to become involved in the project early within the process such that they can work in collaboration with the rest of the design team to achieve the optimum solution. In many cases this can mean the need to provide specific holes in the structural members to accommodate cabling, lugs or bolts for the fixing of bracketry to hold equipment of the sizing of handrails or balusters to accommodate fixtures. The need to facilitate control gear, the location of distribution broads, time-clocks and detectors also all need to be taken into the account. Finally the requirement to provide safe access for maintenance and a clear strategy for both installing the fixtures and then cleaning and repairing them can sometimes require additional measures to be incorporated such as latch-way systems or rigging points for absailers. The earlier in the process all of these issues can be considered the more integrated the lighting will become.

Whilst the above are the key considerations it is recognised that many other factors can come into play. Both capital and running costs drive decision making by necessity. Other issues include the consideration of regular maintenance, the risk of vandalism, the long term replacement of the lighting system including its wiring and the disposal of lamps and equipment at the end of life. The latter is of particular importance as one of the most critical factors that has driven the design of lighting on footbridges in the last twenty years has been the changes in lamp, equipment and lighting control technology.

5. Technology
The background to the lighting of bridges as outlined at the start of this article illustrates that the prevailing lighting technology of the time has played a key part in the manner in which bridges have been lit. When all that was available was ‘flame’ it is perhaps not that surprising that little evidence exists for the design of more permanent lighting solutions.

Whilst gas lighting offered more permanence the mechanisms by which it was required to work also created constraints; the provision of pipework, the ability for lamp lighters to easily reach the mantels and the availability of the gas itself would all have been factors that limited the design.

It was therefore only when electric light became widely available that more elaborate and integrated solutions became possible, though in many cases the requirements for robust schemes that might survive the long term exposure to the elements meant that fixtures sizes and lamps types still provided some limitations, particularly on smaller structures. The need for access for maintenance has also always played a key role in the design of lighting installations.

As has already been alluded to many different electric lamp sources have been developed in the last one hundred years that have been successfully employed in bridge environments: these include the monochromatic yellow light of low pressure sodium, the warm orange glow of high pressure sodium, the cool blue-white of mercury and a wide range of metal halide and fluorescent sources. It has perhaps only been within the last five years however, with the advent of the solid state revolution in lighting through the development light emitting diodes (LEDs), that the possibility of truly integrated lighting on bridges has become a reality. Such technology can not only be miniaturised to fit in increasingly small fixtures but also carefully optically controlled such that both functional and architectural lighting can be easily achieved from sources that can be fully integrated within the structural design. The long life span of LED has also helped mean that maintenance is less of an issue though the failure rate and fragility of the electronics, plus the need to carry out wholesale replacement at the end of life, makes LED far from ‘fit and forget’. The need to house electronic drivers for LEDs also creates an issue; the driver is the component most likely to go wrong and therefore ease of access for replacement is essential. Whilst ‘mains on board’ technology eliminates this requirement the fittings are more bulky and often more expensive.

Despite some of the drawbacks however it is important to evaluate the possibilities offered by LED given the precedent for lighting technology influencing the approach to bridge illumination: The first benefit worth considering is the ability for LED to deliver the light. In all cases the distribution of the light is generally controlled by the optical arrangements of the lighting equipment. Where more traditional sources are employed such as discharge and fluorescent lighting the design of the reflectors and/or lenses to the fixtures themselves are the key to not only carefully controlling the light but also reducing unwanted characteristics such as excessive glare. The physical size of the lamp plus its relationship to the reflector that then go on to influence the overall size and design of the fixture, which in the case of exterior luminaires is often quite bulky. Whilst the principle is much the same with solid state sources such as LEDs a much wider range of different options exist from chips that sit within reflectors or that are encapsulated within their own micro-optical arrangement such that a smaller number of highly efficient points of light can deliver not only a considerable amount of light but also a specifically tailored distribution. Additionally these sources can be easily grouped according to the requirements of the bridge such that they can be accommodated directly into key elements such as handrails, balustrades, steps, etc. Whilst the spotlighting and floodlighting of the structure, soffit and other architectural component of the scheme are still likely to be carried out using LED’s housed within more conventional forms these are becoming much smaller or possessing lower profiles making them easier to conceal or integrate into the overall design.

Secondly, beyond the manner in which the optical design distributes the light, whether as a flat wide soft diffused wash, narrow focussed beam (or any manner of distributions that exist between those conditions) the lighting has always been able to be further controlled through the use of accessories such as louvres or cowls or by simply being able to angle or direct the fitting itself. In respect of the lighting of footbridges it is often advantageous to be able to adjust the fitting itself given the often complex nature of the forms that are being lit such as arches, cable stay arrangements, cambered soffits, etc. The only disadvantage of adjustment in the fitting is the considerable effort that is require as part of the final commissioning of the lighting system to ensure that all the fixtures are properly adjusted, that and the risk that they are then later put out of adjustment as the result of cleaning and maintenance regimes. Certainly once the lighting on any bridge is properly focussed and adjusted there is a lot to be said for having the ability to ‘lock it’ into position thereby guaranteeing that the distribution remains as the designer intended. Again, the newer LED solutions can obviate the need for many of these requirements through the ability to incorporate micro-louvres within the body of the fixtures themselves of for the optical arrangements to be more precisely tuned to match the form they are illuminating such that the need for final adjustment is reduced. The fact that lamps themselves have such a long life also obviates the need for maintenance crews to do anything more than to clean dirt off the face of the fixtures on an annual basis.

The final aspect to be considered with respect to new technologies is the manner in which the lighting is controlled. In the past this was often as simple as the lighting being on or off, perhaps controlled by a photocell and/or time-clock. With the advent of lower cost digital control systems providing flexible switching or dimming arrangements to allow different lit elements of the bridge to be controlled independently of each other is now cost effective and easy whilst the dimmability of LED also allows the relationship between differently lit elements of the bridge to be visually balanced. Access to proper lighting control can also assist with the automated operation of the lighting. Incorporating astronomic time-clocks which account for the changing time of dawn and dusk can also provide greater flexibility which when used with programmable photocells the scheme can respond to the presence of natural light. Additionally where movements on a footbridge are limited at certain times of night presence detection can also be employed such that the lighting dims up as someone approaches the bridge and dims back down again once they have used it. This method can be effective in saving energy and reducing lamp maintenance.

6. Case Studies
The following case studies briefly illustrate how the above approach to lighting has been both developed and applied in the case of four contrasting lighting schemes for footbridges. The case studies take an older example in respect of the Golden Jubilee Bridges in London (Hungerford Bridge), the design of newly completed bridge for the Lower Hatea Crossing in Whangerai, New Zealand, the lighting for the Sackler Crossing at the Royal Botanic Gardens, Kew, where darkness played a critical role and the lighting of Infinity Bridge where blue light was employed to great effect.

6.1 Golden Jubilee Bridges, London, UK (Old)
Client: Westminster City Council
Architect: Lifschutz Davidson Sandilands
Engineer: WSP
Contractor: Costain
Lighting Design: Speirs + Major
Completed: 2002

The lighting was developed in conjunction with the architect Lifschutz Davidson Sandilands. Their competition wining scheme allowed for two new footbridges to be ‘hung’ off an existing railway bridge across the River Thames.

The decks were lit through by metal halide spotlights concealed within the structural ‘angel wings’ that terminated the cable stays at the top of the pylons. This not only provided the illumination to the deck but had the effect of lighting the inner face of the cables. The lighting was brighter immediately underneath the arrays which created a rhythm of light such that the lowest levels of illumination occurred in the gaps between the cables, which in turn promoted views. The verticals of the balustrades were also lit both on the inside in white light with the spill light being captured through blue lenses to provide an accent to the outside. This highlight was complimented by the use of beacons of the same colour on the top of each pylon.

It was agreed to illuminate the main pylons. This was done such that only the inner faces of the pylons were lit. Not only did this help reveal the form and have the benefit of improving the perception of safety on the bridge but also allowed the presence of the footbridge on the far side to be seen from a distance, thereby reinforcing the architect’s concept.

The lighting scheme was popular when first switched on as its strong visual appearance created a memorable identity. Whilst a clear strategy for maintenance was resolved at the outset continuous under-investment meant that the original scheme became quite ragged. It was eventually replaced with RGB colour change LED lighting in 2012 in time for the London Olympics. Whilst the new solution follows the exact concept of the old the use of RGB has unfortunately resulted in a diffused, cold ‘dirty’ white effect rather than the warm, crisp whiter solution of the original.

6.2 Lower Hatea Crossing, Whangerai, New Zealand (New)
Client: Whangerai District Council
Architect: Knight Architects
Engineers: Peters and Cheung/Eadon Consulting/Northern Civil
Contractor: MacDow Transfield JV
Lighting Design: Speirs + Major
Completed: 2013
Photographer: Patrick Reynolds

Won as a competitive tender with Knight Architects in 2011, this 265m tidal river estuary crossing is a key component in the developing local road network, designed to reduce congestion in the city centre and improve access to Whangarei Heads and the airport.

Speirs + Major’s challenge was to highlight the “J” shaped ‘fish hook’ primary structure to create a night-time iconic image for the new crossing, while providing the necessary highway authority requirements for the various bridge users and considering the local dark sky environment as a natural resource. A tilting bascule structure, the “J” fish hook pivots to open the bridge for passing vessels. All luminaires are located at low level to reduce any vertical visual impact on the bridge design. The lighting has been planned to ensure the primary structure is lit both in the closed and open positions and considers the moving transition in between.

Each luminaire was chosen with consideration given to spill light, glare and maintenance. Where possible, luminaire positions and light were used for dual purpose. The highway lighting is provided from low level linear LEDs at the crash barrier, the pedestrian deck lighting from lighting built into the base of the balustrade structure, and the structural “J” lighting from both the base of the balustrades as well as LED projectors. Careful directionality and focusing were part of the design to ensure light was placed where required and any light pollution avoided.

Speirs + Major were fully involved in the concept and design development of the Lower Hatea River Crossing and were consulted on the implementation during the construction phases of work.

6.3 Sackler Crossing, Royal Botanic Gardens, Kew, UK (Dark)
Client: Royal Botanic Garden’s Kew
Architect: John Pawson
Engineer: Buro Happold
Contractor: Costain
Lighting Design: Speirs + Major
Completed: 2006

The S-shaped form of the Sackler Crossing appears to float just above the surface of the lake at the Royal Botanic Gardens of Kew. Constructed on a concealed steel frame, the deck consists of granite planks with solid bronze cantilevered vertical uprights providing the balustrade. The bridge reflects in the water and the water is reflected in the bronze of the uprights.

The lighting treatment is simple, understated and in tune with the mercurial nature of the design. Just under 1000 custom high-output white LED uplights are recessed in the granite planks of the bridge deck at either side, between each bronze upright. They gently illuminate the inner surfaces of the uprights, as well as reflecting light on to the deck and people crossing the span. The small-diameter fittings were developed with the single 1W LEDs set low down to minimise the visibility of the source. An additional frosted glass disc hides the bezel and reduces glare.

The crossing is put in context after dark with gentle highlighting to specimen trees on the adjacent island which creates visual interest and a focal point in the landscape. Cool white ceramic metal halide spots and floodlights are combined, some fitted with custom blue toughened-glass filters. Depending on the direction of approach across the bridge, the trees are either silhouetted in blue light with the front face picked out in white light, or vice versa.

As the Royal Botanic Gardens remain mainly dark at night, the bridge softly shimmers in the darkness as if lit by moonlight and reflects in the water of the lake.

6.4 Infinity Bridge, Stockton-On-Tees, UK (Blue)
Client: Stockton Council
Architect: Stephen Spence
Engineer: Expedition
Contractor: Balfour Beatty Civil Engineering
Lighting Design: Speirs + Major
Completed: 2007

The brief called for an iconic structure as part of the Stockton-on-Tees regeneration of the North Shore site. The resulting footbridge links the north and south shores and provides better access to business and jobs in the area. Designed by Expedition Engineering, the slender bowstring bridge cuts a distinctive silhouette across the river. A 230m-long concrete walkway is supported by a pair of asymmetric steel arches that appear to skip across the river almost like a pebble skimming water.

Speirs + Major designed the lighting in such a way that the iconic twin arches reflect in the water at night to form the mathematical symbol for infinity (∞). Cold white light was used to reveal the structural form and create the sense of a floating wave hovering just above the deck. The designers then bounced blue light off the water to light the underbelly of the deck and form a blue zone above the water. All the lighting equipment was carefully concealed. Floodlights are mounted on outriggers away from the bridge so that pedestrians aren’t aware of the fixtures or disturbed by their glare.

An unusual aspect of the project is the way light responds to the presence of people. Along the surface of the deck, lights react to the movement of pedestrians, guiding them down the walkway and signalling the approach of oncomers. The effect is created by low-energy, blue and white LED units concealed under the handrail. As people cross the bridge, handrail sensors trigger a change from blue to white, leaving a ‘comet’s trail’ of light in the pedestrians’ wake.

7. Conclusion
This article has briefly examined the background, approach and key design criteria that are required to be considered when illuminating footbridges. It has also touched on the way that changes in technology are allowing much greater integration of the lighting into the design of footbridges as long as provision is made for the light early within the design process. Finally it looked at some examples of how lighting has been applied through four cases studies – old, new, dark and blue. In conclusion it is clear that whilst there is some tradition of illuminating footbridges the art of lighting such structures is a relatively new and developing form that can not only make a direct and positive contribution to the experience of those who use a footbridge after dark but also to those that view it within its context. Whilst there are many important considerations to take into account such as safety, security, identity, flexibility, accessibility, sustainability, maintenance and cost if the lighting design is carefully developed in collaboration with the bridge designers using the benefits of new and exciting technologies such that it becomes a truly integrated part of the overall design then lighting can add considerable value to the overall project by not only delivering on the functional aspects of the scheme but by also celebrating the form of its architecture.