The Eastway tunnel is a 290m long structure on the A12 – one of the main trunk roads into London. The original lighting consisted of cornice mounted twin 58W fluorescent luminaires for the night and basic day lighting, interspaced with 250W and 400W HPS luminaires for the boost lighting. Lighting control was via a photometer and contactor based system.
Due to the restricted headroom in the Eastway tunnel it was not possible to mount any infrastructure over the roadway so all new lighting, cabling and control had to be mounted in the cornices over the kerbs.
The new lighting is part of the TRT Verso luminaires range customised with a lens arrangement bespoke for Eastway tunnel – the optics are arranged in a special configuration to achieve both the required road and wall luminance levels. These custom luminaires have 25% of the asymmetric lenses pointing towards the wall and 75% aimed at the road, enabling optimal light levels to be accurately achieved on all surfaces without wasting light and energy. By having the ability to configure the lenses in such a way, exactly the right percentage of lighting is cast onto each surface without over lighting, with a luminaire mounted in the cornice that has not been angled.
Lighting control is provided via a full feedback PLC controlled eMaster system. All control elements are located within the tunnel control room for ease of maintenance. From the control system, DALI networks enter the tunnel and loop through the driver enclosures providing communications to the luminaires. The eMaster uses the photometer mounted at the portal to accurately set the lighting level to the portal conditions required. The DALI drivers are mounted remotely from the luminaires in dedicated enclosures on the tunnel walls.
The dimming scheme offers significant energy savings over a switched stage system as it improves the resolution with which the lighting can match the luminance reduction curve. With this fully dimmed system the lighting can accurately match the requirements of the photometer; If the photometer demands 30% then the lighting will go to 30% output rather than jumping to a fixed stage of 50%, which would use 20% more energy than necessary, or risk underlighting by 5%.