US tunnel to install sodium lamps as ‘LEDs not ready yet’

The operator of a tunnel in America’s north east is set to install high sodium lamps because it claims that ‘LEDs haven’t been tested in a tunnel’.

A spokesperson for the Washington Department of Transportation said the lighting refit of the Mount Baker and Mercer Island tunnels in Seattle would use SON lamps and not LEDs as the latter had not been proven in tunnel conditions.

The spokesperson told local news station KIRO 7, that the improvements would actually make tunnel lighting 50 percent brighter by early 2017. The project is part of an ongoing upgrade to Interstate I-90.

Drivers who regularly use the tunnels have long complained that the contrast between the dark tunnel and the brightness outside often creates a traffic slowdown with people braking as their eyes adjust to the changed light conditions in the tunnels. There’s anecdotal evidence that traffic flows are better on overcast days, when the contrast between the tunnel and the open road is less pronounced.

However, the decision to use the relatively old technology of high pressure sodium over LEDs will be seen as controversial in the lighting industry. Earlier this year, the 10.7 kilometre Toven Tunnel in Nordland, Norway, became the world's longest lit entirely by LED lighting.

In what was seen as a vote of confidence in LED technology for tunnels, the operator – the Norwegian Public Roads Administration - opted for LEDs over traditional technologies to achieve low energy and high controllability.

The lighting has either meets or exceeds all lighting requirements in the relevant standards, with a luminance level in the inner zone of 0.7cd/m2, which exceeds the requirement of 0.5cd/m2. The efficient LED lamps typically use 21 per cent less energy compared to conventional alternatives. When combined with the intelligent lighting controls employed at Toven tunnel, this figure increases to 70 per cent to secure substantially lower energy costs.

The use of LEDs in tunnels is the theme of the world’s first Road Tunnel Lighting conference, which takes place in Barcelona on 8 and 9 October 2015. Entry is free for tunnel operators and consulting engineers. See the full programme and register for a free place at www.tunnellightingconference.com.

Picture: Matthew Rutledge