Tunnel vision

In a first for UK lighting, TfL and Indal WRTL have teamed up to trial a linear LED scheme in the Upper Thames street tunnel in London. Amanda Allen reports

The first ever tunnel fully lit using LEDs was trialed in Holland in 2010. The work of Indal, the Vlake tunnel achieved a 50 per cent reduction in energy costs for the Dutch government. With the international interest the trial generated, it was only a matter of time before other countries followed suit.

Its counterpart is a trial in the Upper Thames Street westbound tunnel in London which TfL anticipates will reduce their energy consumption by 60 per cent.

Dana Skelley is director of roads at TfL and responsible for the strategic road network which includes13 tunnels – more than any other highway authority in the country. “As you can imagine, street lighting, including tunnel lighting, contributes hugely to our energy costs and to our CO² emissions, both of which we were looking to reduce,” explains Dana. “Another important factor we consider is maintenance because we want minimal disruption to the public. That’s why we wanted to look at LEDs – anything that can enable us to close tunnels less frequently is a plus for us.”

For the trial, which will last approximately 12 months, the tunnel has been fitted out with a total of 259 interior and boost lighting T-line LED luminaires from Indal WRTL, as well as their B-Scout control system, replacing approximately 350 250W high pressure sodium lamps.

Less is more

With reductions top of the agenda, the figures TfL are anticipating will be music to the ears of highway authorities the length and breadth of the country.

While TfL are estimating a 60 per cent reduction in CO² emissions, Indal WRTL are being more generous with their figures claiming a 75 per cent reduction could be achieved. In addition, TfL expect that the LEDs will reduce the annual amount of energy required from 368MWh to 68MWh leading to considerable cost reductions.

But it’s not just about cost reductions, according to Neil Morris of Indal WRTL. Other benefits include improved uniformity, visual guidance and colour recognition. “There is improved light distribution with the T-line system through our direct lens approach. When the light passes through the lens it can be accurately directed onto the desired surface providing more flexibility and efficiency by distributing the light directly where you need it. If you covered half the LEDs it wouldn’t change the lighting distribution of that luminaire it would just appear less bright,” says Neil.

Uniformity is also improved throughout the new scheme with a level of 0.99 being achieved. “Because the luminaires are mounted end to end they give a uniformity of 0.99, which is almost perfect. The former scheme was more like 0.7 resulting in a flickering effect on the driver’s dashboard,” explains Neil.

Maintain me

Maintenance is a major consideration for TfL causing significant disruption to London’s road network each year. The trial acknowledges this through its long life solution and remotely mounted drivers. “There is virtually no maintenance except for the drivers which aren’t mounted in the luminaires; they are mounted remotely. In this tunnel most of the driver enclosures are in the vent shaft which means they can be accessed while the tunnel is still running,” says Neil.

The temperature of the luminaire is controlled through the WRTL Coo-LED system – a combination of low-current, low-density LEDs with a large cooling surface. “Because of this, we don’t need cooling fins on the back of the luminaire, which you’ll find on nearly all other LED tunnel luminaires. Also the LEDs are spread out, helping to keep the temperature down.”

While improved maintenance was an important issue, the improved safety offered by a linear LED solution was also a major drawing point for TfL. “Because it’s white light, you have improved colour rendering allowing drivers to associate different colours and the distance between cars much easier,” says Neil. Neil also claims that the single white line of light down the centre of the tunnel improves visual guidance for drivers, marking corners in the tunnel and helping to keep drivers within their lanes. “The luminaires run back-to- back down the middle of the tunnel giving improved visual guidance and it’s about 25 per cent more efficient than lighting the tunnel from the sides.”

Another important safety issue to consider when designing tunnel lighting is how the drivers’ eyes will adjust to the different light level upon entering the tunnel. In this particular tunnel the lighting at the entrance is bright; being lit by five rows of luminaires mounted closely together which gradually reduce as you drive through the tunnel. “The lighting is bright at the entrance but it’s very expensive to light a tunnel like that all the way through. Based on the speed that you’re travelling, 30mph in this particular tunnel, the lighting intensity is gradually reduced based on how quickly the eye can react to the changing light level. It then rises again as you approach the exit but by not nearly as much,” says Neil.

Test of time

So far the figures seem to stack in favour of TfL and their ambitions of cost reduction but they will be monitoring the scheme closely over the next 12 months to see if the manufacturer’s claims are realised. “We have got 13 tunnels in total and it is our intention to ultimately have all 13 lit using LEDs. But we also want to keep in touch with the technology because it’s changing so rapidly. Doing this trial helps us to understand the different options available – we could find that by the time we do the next tunnel then there may be a different solution available,” says Dana. Whatever the solution, Indal WRTL will be keeping everything crossed in the hope that the trial is a success. I wonder how many luminaires it would take to light the Blackwall tunnel…

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