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Setting the standard for street lighting

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How lighting expert Peter Raynham helped usher in a shift to safer, cheaper, more energy-efficient street lights in the UK.

We found that you needed slightly over half as much white light to get the same result as orange light.

Professor Peter Raynham

In 2003, the British Standards on street lighting were amended to reflect a landmark piece of research that demonstrated that people can identify faces better under white light than the orange sodium lighting conventionally used in cities, and at a lower level of illuminance.

There are signs that people have an aesthetic preference for lower, white light compared with yellow or orange light, but the impact of this change goes far beyond taste – it has significant implications for the environment too. By mid-2013, about 800,000 lanterns across the UK – about 10% of the total number of street lights – had shifted to using white light, equating to a saving of about 64TWh of electricity or £6m per year for local authorities, with the associated fall in carbon emissions.

The person who led this research was Peter Raynham, who arrived at The Bartlett’s Institute for Environmental Design and Engineering (IEDE) in 1996 after working for 20 years in the lighting industry. The escalation of his findings to the level of national significance was partly a result of his long-standing relationships with professional and public bodies, and his history as chair of several British Standards committees – connections that allowed him to place the findings in front of the right people.

10% of UK street lights had, by 2013, shifted to using white light – a saving of 64TWh of electricity or £6m per year.

Source: 'White Light for Street Lighting' (REF Impact Case Study)

Indeed, the impetus for the work came from the industry itself. “In the early noughties, people were noticing that white light seemed to do better – there was anecdotal evidence, but they couldn’t characterise it,” says Raynham, who is now Professor of the Lit Environment at IEDE. “The research answered a need. People knew something was going on, but they wanted to pin it down.”

Testing the theory

Raynham and his team set up a fake street in a disused building and tested the level of facial recognition under a variety of light sources, keeping in mind the premise – established in the early 1980s – that pedestrians needed to recognise each other at a distance of four metres. To their surprise they found that the colour of the light made a significant difference. “We found that you needed slightly over half as much white light to get the same result as orange light.”

The publication of the results in 2003 came at an opportune moment, because the British Standards committee was about to update its guidance on road lighting. “It decided you could drop the level of light by about a third if you used white light,” says Raynham. “Even though white light sources were slightly less efficient than high-pressure sodium yellow sources of the time, you would save about 10% to 15% of your electricity bill if you switched to white light.”

You would save about 10% to 15% of your electricity bill if you switched to white light.

Professor Peter Raynham

The British Standards have since been revised again and are due another update, with more complex formulas to calculate lighting levels, but white lighting remains at its heart and virtually all new street lights now are white LEDs.

Night vision

Raynham notes that there are still “big unknowns” in the field of night vision. For example, “as it gets darker vision tends to distort in a way nobody thought was happening,” he says, explaining that this may be a reason people feel less secure on the roads at night. He has also started researching why certain types of traffic collisions happen more at night.

This type of research that pulls together all facets of urbanism and social science would be much harder were it not for the multidisciplinary environment of The Bartlett, Raynham adds. “We’re not 100% aligned, but we’re all asking awkward questions and some of us occasionally get halfway sensible answers.”

The Institute for Environmental Design and Engineering is pursuing a deeper understanding of the interactions between the built environment and health, human wellbeing, productivity, energy use and climate change. It is part of The Bartlett School of Environment, Energy and Resources (BSEER) in UCL's Faculty of the Built Environment. Find out more: https://ucl.ac.uk/bartlett/environmental-design

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