CAROLINE HAYES examines the regeneration of the lighting scheme at a UNESCO World Heritage Site in England, where modern controls and solid-state lighting are used to enhance the building’s features while project specifiers remain sensitive to the architectural integrity of the monument as well as potential light pollution concerns.
In the north of England, the town of Durham is guarded by dual, imposing monuments — its castle and the city’s cathedral. As the 25th anniversary of the castle and cathedral’s status as a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site approached, a regeneration of the lighting scheme was planned. The aim was to enhance the aesthetics of the Norman monuments, highlight the architectural features, subtly distinguish the two buildings when viewed from a distance, vary lighting for special events while protecting the local wildlife, and significantly reduce energy costs.
William the Conqueror commissioned the castle to be built in 1073, to defend the settlement on the peninsula along the River Wear. It became the residency of Bishops of Durham, and buildings were added and altered to suit the needs of the day. Across the green is the cathedral, which dates from 1093 and is acknowledged as the largest example of Norman architecture in England. It is the only cathedral considered to retain most of its contemporary Norman craftsmanship and one of the most important examples in the UK.
|The LED-lit entrance to Durham castle.|
The World Heritage Site monuments were lit by large, exterior, high-power-projector high intensity discharge (HID) floodlights placed at ground level that had been installed in the 1960s. They were deemed to be at the end of their serviceable life and also outmoded. There was no attempt to conceal them and they gave a flat wash of light across the buildings, rather than accentuating features. In addition, the lamps and the control gear used were not energy efficient.
A new scheme was required to reflect the modern role of the castle and cathedral, where nighttime visitors are encouraged, and where special events can have a customized lighting system to add aesthetic appeal or highlight areas of interest. Another requirement was to save energy — a target of 33% reduction was set — as well as to reduce light spill for the student accommodation quarters in the castle, and also for the Pipistrelle and Natterer bat populations locally.
|The new solid-state lighting system accentuates some of the historic stonework at Durham Castle.|
Stainton Lighting Design Services and Urbis Schréder designed the scheme, which was installed by AK Lighting and Signs. Anthony Smith, director, Stainton Lighting Design Services explained that the plan was to change the viewing experience during the hours of darkness and to provide a landmark lighting scheme, which would stimulate the area’s nighttime economy.
There was also some confusion among visitors who viewed the castle and cathedral from the city below — from certain viewpoints, the cathedral tower appeared to rise from the castle. A way to distinguish the two buildings, using the lighting scheme, was added to the plan.
"A primary aim was to maintain a subtle, but observable contrast between the color temperature of the castle and cathedral," said Smith. This would allow the site to be viewed as a coherent World Heritage Site, while allowing the individual buildings to retain their identities. To offer an alternative viewing experience by day and night was another priority, which required luminaires to be located unobtrusively where they could not be easily seen. The floodlights were placed closer to the buildings than the ones they replaced, between 1 and 3m (or 3–9 ft) from the buildings. The closer positioning also eliminated the need for additional window reveals as the new system produced less light spill into the buildings’ windows. This was a particular benefit in the castle keep and the parts of the cathedral that are used for student accommodation.
|The Norman architecture of Durham Castle and Cathedral, seen from the city of Durham below.|
The proximity of the customized Urbis Schréder Neos 1, Neos 2, and Noctis 225 LED floodlights and bespoke Philips eW Reach floodlights serve to highlight the fabric and fine masonry work of both buildings without being visible themselves. Paul Johnson, Urbis Schréder’s regional sales manager, north of England, explained the pains that the project went to in making the lighting unobtrusive, with the Neos being coated in a color that was specifically selected to match the stonework against which it was positioned. Similarly, the Noctis floodlights were positioned flush into the ground so they could light up specific areas without being visually intrusive. The castle courtyard, Johnson added, is an area of high traffic and so again, unobtrusive lighting was a requirement for the free-flow of pedestrian foot traffic. High-power Cree XP-E and XR-E LEDs were used in the floodlights, with seven optic types provided by Carclo.
Each light was tailored to where it was to be located. Johnson declared, "All Neos lights are, to some degree, bespoke, but none as bespoke as this — 95% was non-standard," he said, referring to the individual light combination of the 64 LEDs used in each light. Stainton specified the combination of wide, medium, and narrow, and horizontal and vertical beams, including those with 90˚ for a low horizontal line or a long vertical line on particular areas. For each floodlight, a specific position was designated, with a specific lens combination.
|Less light spill throughout the property benefits the students boarding in the castle keep quarters during term time.|
Despite the options and configurations, all variances in color temperature were within 100K. The customization was also practical. Smith points out that although the specification for each luminaire was bespoke, the selection of LEDs will allow replacements to be provided with the exact same characteristics.
Some of the detail that the lighting made more prominent was commented on by long-term members of castle staff, who reported that they had not noticed some of the interesting stonework features before.
Part of the design concept regarding distant views of the buildings was to provide a subtle but observable contrast between the color temperature of the castle and the cathedral. Two color temperatures were selected for each building — 3000K and 3500K for the castle, and 3500K and 4000K for the cathedral. "The variance in color temperatures on each building offers contrast and depth to the abutment areas," commented Smith. "However, as the main color temperatures are 3000K on the castle and 4000K on the cathedral, the color difference of 1000K is still evident when the buildings are viewed from a distance."
The historical nature of the buildings, parts of which stood on consecrated ground, meant that great care had to be taken with situating the luminaires. A key planning constraint, reveals Smith, was that the existing cable network was to be reused wherever possible and, where clipped cable was replaced, the fixing holes had to be reused. Although 46 luminaires were removed and more than 250 installed, no new holes were able to be drilled into the fabric of either building, meaning that cable power or control had to use existing cable routes. There are only two locations where a luminaire has been set in an existing location. The use of lead P-Clips throughout was specified, and these were manufactured by contractor AK Lighting and Signs specifically for the project. This seamless positioning all had to be achieved despite the 500% increase in the number of luminaires used throughout the buildings.
The archaeological heritage also meant that there was a risk of finding buried artifacts that could cause costly delays. This was another reason to use only existing cable routes or previously undisturbed ground. Equipment was limited to being buried 300 mm below ground level. Groundwork was therefore undertaken early in the installation phase to minimize the impact of any archaeological finds. There were constant archaeological checks, in case any articles of interest were found. As testimony to the care taken, more than 1 km (or more than 3000 ft) of new underground cable was installed — the majority within the cathedral’s medieval graveyard — without any delays to the project.
|Close but discreet LED-based floodlights illuminate the Norman architecture that inspired later Victorian-Gothic design at Durham Castle.|
Cabling and luminaires on the roofs of both buildings represented a particular challenge. A robust platform was needed to mount each luminaire but also had to provide termination control and power circuits. The platform also had to be unfixed so it could be moved for repairs to the lead roofing; it had to be heavy enough not to shift or tip in the wind, but light enough to be taken up to the roof manually, as a crane or similar was not practical in this case. The solution was to carry component parts up to the roof and assemble the roof-mounted luminaires there. As a result, no part weighed more than 20 kg (approximately 44 lb). In all, eight mounting arrangements were used. The design was also used for four lanterns in the courtyard, which required mounting height of 1.4m (approximately 4 ft, 8 in.) and 0.5m (approximately 1 ft, 7 in.) outreach from a free-standing bracket.
Another vital part of the project was to preserve the wildlife around the area. A bat survey was undertaken and identified three existing roosts for bats. Most of the bats around the site are Pipistrelle bats but there are also Natterer bats, which are relatively rare and which forage in trees and vegetation. Both species are characterized by roosting in the crevices of old buildings.
To respect the wildlife, no roosts were lit and foraging sites or commuting routes were not lit directly. In these areas, timers and movement sensors were used to switch lighting on 90 minutes after sunset and off 90 minutes before sunrise.
The LED lighting used high output bins with low or nonexistent emission of ultraviolet (UV) or blue light to mitigate the environmental impact of the scheme. Trees and ground cover were not lit and existing lighting of trees and ground cover was removed. Where lighting was necessary, it was directed and featured low spill. A close offset approach to lighting buildings avoided unnecessary spillage. Louvers and glare guards were fitted, as appropriate, to luminaires to reduce spillage.
An ecologist inspected the final, installed scheme and the design was commended for its ecological considerations.
One of the main aims of the original plan was to design a control system that could reconfigure the lighting for specific events. Rather than a hard-wired system, which would require new cable routes, a partly wireless DMX (Digital Multiplex) system was decided upon. This is one of the most common protocols used with LED technology and offers control and flexibility, says Smith. Johnson believes this is the first part-wireless DMX implementation.
Luminaires were grouped into zones that connect wirelessly to the main DMX controller. Each zone has a DMX receiver, which uses a traditional cable link between the luminaires to form the DMX network. A problem encountered in constructing the wireless systems was that the building did not always lend itself to an ideal line of sight between transmitter and receiver. Some of the walls are 2m (6 ft) thick. The radio signals, says Johnson, were sent over the building and around with repeaters and aerials. Radio surveys verified the prime locations for the two transmitters and five receivers used in the wireless system. Remote access to the DMX controller was via the LPC1 lighting controller from Pharos. It has 512 channels and real-time control of playback selection and lighting levels for lighting sequences and automation. This was also adapted by Urbis, who built the housing for the drives and control gear.
As a result, special events can have a specific lighting sequence. There are five to six programs set in the control "HQ" sited in one of the cathedral offices and the porter’s lodge in the castle, but, says Johnson, for "serious slideshows, other sequences can be programmed via a PC to produce color schemes and to highlight particular areas."
One of the main causes for celebration of the project is that it was awarded third place in the Auroralia 2013 Best Initiatives in Urban and Sustainable Lighting category for its energy savings. Despite more luminaires being used than in the original lighting scheme, the target of 33% energy savings was surpassed, with an annual energy consumption reduction of 78%. Smith adds that even if the scheme used the same switching protocol as the original, it would achieve energy savings of 60%. The final installed lighting will save approximately £18,500 (around $30,360) per year in energy costs at today’s prices, he says.
CAROLINE HAYES is a contributing editor with LEDs Magazine.