Peterborough’s updated Longthorpe Footbridge is unusual in using SON-equivalent 1800K LED to replicate the ambience of its original 1970’s lighting.
Originally constructed in 1970, a 30m-long footbridge at Longthorpe in Peterborough, provides a much-needed thoroughfare across the busy A47.
In a project that began in 2022, National Highways has now introduced a new footbridge to replace the old structure, including with new shallow-access ramps at 5% gradient to make it more accessible for cyclists, walkers and wheelchair users.
What is intriguing about the scheme from a lighting perspective, however, is that the new structure is lit, yes, by modern LED lighting, but to just 1800K, so in essence to match the old yellow-hued SON lighting.
The scheme was provided by DW Windsor, which worked with engineering, management, and development consultants Mott MacDonald to provide lighting for the road, bridge, and ramps.
The scheme called for replacement columns on either side of the footbridge, with eight ‘Kirium Pro’ luminaires providing illumination for both the road and overpass.
However, to maintain the ambience provided by the original SON lamps along the A47, a special request was made to implement a lighting solution that matched the old light levels and colour temperature.
‘HIGHLY UNUSUAL’
‘It is highly unusual to have high-pressure sodium, or a high-pressure sodium-equivalent, on a stretch of fast road, as a new scheme. So, we were not expecting that. But this scheme shows that it can work,’ concedes Alan Grant, design and development director at DW Windsor.
The 1800K LED lighting was provided by manufacturer NICHIA, which had developed a range of LEDs to be an ideal mercury-free alternative to high-pressure sodium lamps.
‘Talking with NICHIA, they told us they had a SON-equivalent 1800K LED. SON is probably about 1950K, but an LED and a SON lamp at 1950K don’t look the same. So, they reduced the colour temperature to get the corresponding appearance,’ Alan explains.
‘So, we were aware of it, and then this project came along, which was for functional street lighting. We had been expecting this lamp would have been more for people who wanted something more heritage, or for ecological reasons, perhaps for schemes in an Area of Outstanding Natural Beauty or where the colour of light enhanced the colour of the stone.
‘Our initial thought was, “a SON-equivalent in a functional product, really?”. We were pretty surprised, as it is a main road. But they wanted something to blend in with the existing HPS scheme, and so, of course, we looked at what would be the best solution. We knew we had the NICHIA product, so then it was a question of matching the light/lumen output that was required. We did the work and delivered the products.
‘It really does show that customers can have what they’ve had since the 1950s, or probably even before then, everything from high-pressure sodium all the way up to metal halide equivalents but now as LED. You can have exactly the same appearance of light from LED. Your colour rendering will improve, your life goes through the roof and your energy use will fall through the floor. So, it is fantastic.
‘The takeaway of this, for me, is that nowadays you can have the appearance of the colour of the light that you want. If you need to match to what you’ve had before, you can now have that. It’s now about what do you want to use, and the reasons behind that. It all just adds to getting what the specifier wants,’ Alan adds.
- This is an abridged version of the cover article that appears in the October edition of Lighting Journal. Click on the link to the edition to read the full article.