E&T spoke to the engineers behind the lighting architecture across London’s recently opened Elizabeth line which aims to promote a safe and efficient passenger experience.

Using LEDs to light up the stations, escalator shafts and concourses of the Elizabeth line was a bold move from Transport for London; especially as when they decided on its use back in the late 2000s, LED technology was yet to break into the lighting world.

But this did not stop Paul Kerrigan, the lead electrical engineer responsible for Crossrail’s line-wide lighting solutions and uninterruptible power supply, and his team from taking the plunge to make this a reality.

In fact, the Elizabeth line is one of the first sub-surface infrastructure projects to be lit entirely by LEDs, and the decision to use the technology was based on industry evidence that its use will help reduce energy consumption and maintenance requirements.

“We decided on its use during the very early development stages of LED technology. We had prototyped none of the designs then – it was purely artistic impressions and drawings of the concept,” Kerrigan tells E&T. “So, when it came round to design, we had to embrace the growing technology to develop the products.”

The new line traverses the capital, from east to west, with its entire central section – from Liverpool Street to Paddington – lying underground. The Crossrail team said the route made lighting design critical, not only for passenger safety but also for enhancing their experience within the subterranean environment. “The general use of indirect lighting within the concourses, escalator tunnels and platforms emphasises the spatial envelope rather than drawing attention to the luminaires themselves,” Kerrigan explains.

As a result, the Crossrail team used the light-grey, matt-textured, glass-reinforced concrete lining of the station and escalator tunnels to reflect light onto the passenger areas. This helps “create a sense of spaciousness within the underground environment”, according to Kerrigan.

Specialist LED lighting designer and manufacturer Future Designs created three bespoke lighting solutions that passengers will experience across the line: the Ikon uplighter, Ikon Emergency luminaire and the Plinth luminaire. David Clements, chief executive of Future Designs, explains its LED technology is “ultra-powerful” and will reduce the whole-life cost of the project.

Future Designs’ Ikon products sit on the wayfinding totems, which incorporate the company’s emergency lighting. It is an uplight designed to illuminate the area via reflection from the curved ceiling. It also incorporates emergency lighting, fire alarms and public help points.

“All the lighting on those totems, which is the only light source in that area, was a conceptual design that David developed,” Kerrigan explains. “And its process from concept to the end product flourished over time to what you see [on the line] today.”

Image credit: Paul Kerrigan BEng CEng MIET

The totem is the primary source of lighting in the station lower concourse; it combines wayfinding signage with the top section comprising a high-powered LED uplighter. The totem also houses six emergency lighting units located at various points both vertically and horizontally on the totem body. The team spaced such totems at 9m intervals, illuminating a tunnel area of 8.1m in diameter.

The luminaire provides uplighting onto the GRC wall and ceiling cladding material and distributes a consistent lighting level onto the floor surface, providing horizontal and vertical illuminance of 150 lux and 0.5Uo (uniformity). The top section of the luminaire is constructed from aluminium and acts as a passive heat sink, which controls the ambient operating temperature of the LED units (limiting them to 35°C) to maintain and prolong the life of the LEDs while also acting as a distinctive architectural feature.

The Crossrail team incorporated glass-laminated micro louvre into the totems located nearest to the base of escalators, to mitigate any direction glare that could be seen by passengers. They designed the totem for the subsurface environment, meeting the same requirements as the platform lights.

Meanwhile, the team designed the lighting levels on the escalators to meet the London Underground’s task-based ‘Lighting of Underground Assets’ document, which provides guidance for designers to provide a safe lighting level, enabling the effective performance of all task-based activities performed by the actions of passengers and staff, including the visually and sensory impaired.

The Crossrail team used a variation of lighting levels, from 200 lux on the horizontal plane at the point where passengers step on and off escalators, down to 100 lux on the vertical plane, which allows passengers to read display information.

The team also aimed for the illuminance to be relatively consistent across the line, with a uniformity (U) figure of 0.75 at the stepping-off point on the escalators, down to 0.4 U for general illumination of the concourse circulation areas. The design also complies with the London Underground’s requirement for all its lighting to have a colour-rendering index of 80 (Ra) or above – this is to improve safety and passengers’ visual experience.

Kerrigan and Clements told E&T that creating the lighting for the escalators was a particular challenge. “We wanted to give passengers a lighting level that would provide people with confidence and safety when travelling on the escalator as it is a rather confined space,” Kerrigan explains, adding that the lighting sits at the height of an average person’s waist. A secondary light source is a ribbon of LEDs set into the sides of the escalator to light the treads.

One challenge the team had to overcome on the line was the glare from the lights when passengers step on and off the escalator. “Although the luminaire on the escalator is static, people coming past it are moving, so it creates a moving light,” Kerrigan explains, stressing that the uplighters’ main task is to enhance the CCTV cameras, ensuring there is no glare should Crossrail need to use the imagery. “There was a huge amount of development to take away as much glare as possible,” Kerrigan adds.

Following many designs and tests, Future Designs developed a luminaire that tackles this issue – a design which Crossrail says is “unique” because it offers a high level of light output (50,000 lumens) “while glare is virtually eradicated”. And to achieve this, the LED light engine – the firm’s Plinth luminaire – has an optical arrangement comprising three layers of diffusion to provide a homogenous, uniform appearance with a 70-degree beam angle.

Image credit: Paul Kerrigan BEng CEng MIET

The escalator tunnel is illuminated by two independent lighting sources: an LED tape, which provides a compliant lighting level on the escalator tread (150 lux and 0.08Uo (uniformity)), and a luminaire recessed into the escalator deck. The deck light provides the vertical illuminance and the perception of a guiding light that will focus passengers to concentrate on the direction of travel.

The luminaires are spaced at regular intervals of 1.87m centres along the length of the escalator central deck and are 1.5m-long x 305mm-wide. The LED light engine has an optical arrangement comprising three layers of diffusion, which include a primary specular beam cover providing a homogenous uniform appearance, with a 70-degree beam angle.

Crossrail also took colour temperatures of the LEDs (CCI), across different sections of the line, into account to help guide people through the subterranean stations. Cool white lamps – with a colour temperature of 5,000-7,000K – are used in the transition spaces, such as its escalator tunnels and cross-passages, to encourage people to keep moving, while wayfinding areas and platforms, where people gather, have warm white lamps with a colour temperature of 3,000-4,000K.

For this, Kerrigan and his team drew from many American studies that have shown that using different colour temperatures in lighting can affect people’s movements in large public spaces as they are more drawn to areas with warmer lighting temperatures. “That’s the natural progression of movement within lit-up areas,” Kerrigan says. And Future Designs needed to take this knowledge into consideration when developing the products now seen on the line.

With the totem lights, the biggest challenge Future Designs had to overcome was getting rid of the heat from the LEDs. Here, the firm calculated the dimensions of the heatsink, which ensures heat is dissipated from the LED system, ensuring the longevity of the source. “It took us nearly two and a half years to work out a means to get rid of heat by drawing it downwards to a series of heatsinks,” Clements explains, adding it was one of the most difficult products the company has developed.

The luminaires used here are large – the units are 1.5m long, 305mm wide and weigh 85kg, and are spaced at 1.87m centres along the length of the escalator deck. And as well as the LED PCB, each unit contains an LED control gear. “If something fails, we can remove the entire light fitting and return it to the manufacturer,” Kerrigan says.

Meanwhile, two operatives can remove lighting fixtures on the escalator by standing on a stopped escalator. “Most fittings above the escalators are only accessible from scaffolding, which has to be done in engineering hours – so we never intended to put lights above escalators on Crossrail,” Kerrigan says, describing it as the “cleverest light fitting” on the line.

Both Kerrigan and Clements agree that the lighting infrastructure makes the Elizabeth line unique to all its predecessors seen across the London Underground and that they have met their goal to create a soothing environment to enhance the passenger experience. “We wanted to create a relaxed commuting environment that is the opposite to the poorly lit and cramped environment of the Central line, for example,” Clements admits. “And we believe that the lighting has a massive amount to do with this.”

Kerrigan adds that the lighting design and installation line-wide ensures passengers have a safe journey. Not only does the use of colour temperature and indirect illumination enhance different areas, but the lighting also accentuates the many architectural features across the project, allowing for a seamless journey ahead. “The Elizabeth line provides passengers with an unrivalled experience,” Kerrigan concludes.

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