What makes people feel safe at night? On the science of street lights

Street lights in Kabul, shortly after they were installed for the first time in 2003. Image: Getty.

Winter is coming: the nights are drawing in and in the Northern Hemisphere the hours of darkness already outnumber the hours of daylight. Research has shown that darkness produces a big fall in the number of people out walking – and a major reason for this is that people feel less safe walking in the dark.

There may be an evolutionary explanation for why people feel less safe at night – we can’t see as well, and this may have exposed our ancestors to greater threat from predators. Nowadays, it’s not so much the prospect of being eaten by a savage beast that concerns would-be pedestrians, but the fear of being mugged or victimised.

Some studies suggest that new outdoor lighting can reduce crime rates in an area, but there is conflicting evidence on this. A large review of research found a link between new lighting and reduced crime rates, but improvements were seen in daylight as well as darkness, suggesting that street lighting is not the only factor. This review has also been criticised by other researchers, and a large statistical analysis found no link between crime rates and switching off or dimming street lighting at night.

Street lights may or may not have an effect on crime, but one thing’s for sure – brighter levels of light do make people feel safer when walking at night. This can lead to a significant increase in the number of minutes people spend walking each week. It can also reduce the number of people who avoid leaving their homes at night, reduce social isolation, improve physical and mental well-being and increase community pride.

Street lighting can improve the quality of neighbourhood life by making people feel safer – but, even so, it would be unwise to flood our streets with light at night. Street lighting costs money: the UK’s annual bill is estimated at around £220m. Artificial light at night may also have a negative impact on wildlife and the natural world, for example by stunting the growth of frogs and toads and preventing them from laying their eggs.

The skyglow from street lights also means we rarely get to see the true wonder of the night sky, frustrating astronomers and limiting our appreciation of the natural environment. For these reasons, lighting should be used selectively and efficiently – and this requires good guidance to help those responsible for installing and maintaining our street lighting.

The guidelines for street lighting in the UK and many other countries are currently based on questionable evidence. That’s why our lighting research group at the University of Sheffield undertook a programme of research to find out how lighting relates to feelings of reassurance after dark, and improve the evidence on which lighting guidelines are based.


Illuminating evidence

In one recent experiment, we asked people to walk along a number of streets in the city of Sheffield at night and rate how safe they felt. We also asked these people to walk and rate the streets in the day, to create a baseline measure of safety and to account for biases that may occur if safety ratings were taken only after dark.

The difference in safety ratings between the day and night walks told us something about the lighting on that street – the smaller the difference between day and dark ratings, the safer people felt due to the lighting. We compared our participants’ different ratings against measures of the lighting on each street, including the average illuminance (amount of light falling on the street surface) and uniformity (how evenly spread out the lighting was).

Today, average illuminance is the main measure used when installing and evaluating street lighting. But we found that, while increasing average illuminance was linked with improved feelings of safety, uniformity was more important for making people feel safe. So it might be more important to have evenly distributed lighting, rather than bright lighting, to make people feel safer.

Local authorities are undergoing major changes to their lighting, as they replace the traditional orange sodium lamps with new LED lighting. These new LEDs are more energy efficient, which saves taxpayers’ money. They also give councils greater control over the lighting they provide, for example by dimming and switching off when there are no pedestrians about.

Used properly, street lights can improve people’s lives and help neighbourhoods come alive at night. But there’s still a lot to discover about how people respond to street lighting and the impacts it has on society and the environment – experiments such as these can help to light the way.

The Conversation

Jim Uttley, Research Fellow, University of Leeds; Aleksandra Liachenko Monteiro, PhD Candidate, University of Sheffield, and Steve Fotios, Professor of Lighting and Visual Perception, University of Sheffield.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

Air pollution in London is now so bad it’s affecting lung development

Cough, splutter. Image: Getty.

Air pollution is known to contribute to early deaths from respiratory and cardiovascular disease. There is also mounting evidence to show that breathing polluted air increases the risk of dementia. Children are vulnerable, too: exposure to air pollution has been associated with babies being born underweight, as well as poorer cognitive development and lung function during childhood.

Cities including London are looking to tackle the social, economic and environmental costs of air pollution by improving urban air quality using low emission zones. In these zones, the most polluting vehicles are restricted from entering, or drivers are penalised to encourage them to take up lower emission technologies. London’s low emission zone was rolled out in four stages from February 2008 to January 2012, affecting mainly heavy and light goods vehicles, such as delivery trucks and vans.

But our new research, involving more than 2,000 children in four of London’s inner-city boroughs, reveals that while these measures are beginning to improve air quality, they do not yet protect children from the harmful effects of air pollution. It is the most detailed assessment of how a low emission zone has performed to date.

Young lungs

Our study focused mainly on the boroughs of Tower Hamlets and Hackney, but also included primary schools in the City of London and Greenwich. All of these areas experienced high levels of air pollution from traffic, and exceeded the annual EU limit for nitrogen dioxide (NO₂). What’s more, they have a very young demographic and are among the UK’s most deprived areas.

Between 2008-9 and 2013-14, we measured changes to air pollution concentrations in London, while also conducting a detailed examination of children’s lung function and respiratory symptoms in these areas.

Every year for five years, we measured the lung function in separate groups of 400 children, aged eight to nine years old. We then considered these measurements alongside the children’s estimated exposure to air pollution, which took into account where they lived, and the periods they spent at home and at school.

Our findings confirmed that long-term exposure to urban air pollution is related to smaller lung volumes among children. The average exposure for all children over the five years of our study was 40.7 micrograms of NO₂ per cubic metre of air, which was equivalent to a reduction in lung volume of approximately 5 per cent.

Changes of this magnitude would not be of immediate clinical significance; the children would be unaware of them and they would not affect their daily lives. But our results show that children’s lungs are not developing as well as they could. This is important, because failure to attain optimal lung growth by adulthood often leads to poor health in later life.

Over the course of the study, we also observed some evidence of a reduction in rhinitis (a constant runny nose). But we found no reduction in asthma symptoms, nor in the proportion of children with underdeveloped lungs.


Air pollution falls

While the introduction of the low emission zone did relatively little to improve children’s respiratory health, we did find positive signs that it was beginning to reduce pollution. Using data from the London Air Quality Network – which monitors air pollution – we detected small reductions in concentrations of NO₂, although overall levels of the pollutant remained very high in the areas we looked at.

The maximum reduction in NO₂ concentrations we detected amounted to seven micrograms per cubic metre over the five years of our study, or roughly 1.4 micrograms per cubic metre each year. For context, the EU limit for NO₂ concentrations is 40 micrograms per cubic metre. Background levels of NO₂ for inner city London, where our study was located, decreased from 50 micrograms to 45 micrograms per cubic metre, over five years. NO₂ concentrations by the roadside experienced a greater reduction, from 75 micrograms to 68 micrograms per cubic metre, over the course of our study.

By the end of our study in 2013-14, large areas of central London still weren’t compliant with EU air quality standards – and won’t be for some time at this rate of change.

We didn’t detect significant reductions in the level of particulate matter over the course of our study. But this could be because a much larger proportion of particulate matter pollution comes from tyre and brake wear, rather than tail pipe emissions, as well as other sources, so small changes due to the low emission zone would have been hard to quantify.

The route forward

Evidence from elsewhere shows that improving air quality can help ensure children’s lungs develop normally. In California, the long-running Children’s Health Study found that driving down pollution does reduce the proportion of children with clinically small lungs – though it’s pertinent to note that NO₂ concentrations in their study in the mid-1990s were already lower than those in London today.

Our findings should encourage local and national governments to take more ambitious actions to improve air quality, and ultimately public health. The ultra-low emission zone, which will be introduced in central London on 8 April 2019, seems a positive move towards this end.

The scheme, which will be expanded to the boundaries set by the North and South circular roads in October 2021, targets most vehicles in London – not just a small fraction of the fleet. The low emission zone seems to be the right treatment – now it’s time to increase the dose.

The Conversation

Ian Mudway, Lecturer in Respiratory Toxicology, King's College London and Chris Griffiths, Professor of Primary Care, Queen Mary University of London.

This article is republished from The Conversation under a Creative Commons license. Read the original article.