Chapter 1: Understanding Light

Seeing clearly: How lighting can make London a better city

Chapter 1: Understanding Light

A desire to illuminate

A deep, primordial response to light and dark is a constant across humanity. The dualism represented by these different states is at the heart of many philosophies, religions and beliefs. Darkness is commonly associated with danger, death and transgression, whereas light connotes life, salvation and goodness.

Perhaps because of these powerful associations, most of us rarely stop to consider the mechanics of light and dark. Light is something that makes us feel secure, so the idea has often been to provide what we think is “enough” of it. This has been a major motivation for outdoor lighting in London since its beginning.

Safety and lighting in London – a very brief history

The early history of street and public lighting in London reflects the concerns of the time. In the medieval era violence in the city was endemic, and the streets were dangerous places to be after dark. 5 At times people were simply forbidden from walking the streets at night, but on special occasions like holidays or feasts such restrictions would not be feasible, so lighting was required. 6

The earliest record of any public decree on lighting dates from 1405, with private citizens who lived on major routes being required to hang lanterns outside their houses on Christmas Day to ensure safe passage. Seasonal winter lighting became a fixture ten years later. In the following centuries, the provision of public lighting continued very much with safety in mind. Kensington Road, along the south side of Hyde Park, was such a notorious spot for robberies by highwaymen that in 1692 it became the first road in Britain to have glazed oil lamps set up along its length. 7

The advent of gas lighting in the early 19th century, followed by electric lamps in the late Victorian period, would exponentially increase the spread and uptake of street lighting in London. However, despite the vast changes in society and technology across the centuries, the provision of lighting in the public realm is still understood primarily through the lens of safety, much as it was five hundred years ago.

Safety, security and lighting

This section unpicks some commonly held assumptions about the relationship between light, safety and security. Rather than making claims about the efficacy of lighting as a standalone intervention, it discusses, with reference to the evidence, how lighting plays a role as one tool among many in placemaking and management.

Terminological clarity is also important here. There is an intuitive distinction between safety, which refers to the danger caused by accidents, and security, which refers to danger caused deliberately by other people (of which the most serious incidents could include violence).

Separating these two concepts is important, as the impact that lighting can have on each of them is quite different. The following section discusses how lighting relates to each one, and what all stakeholders should bear in mind when considering a lighting intervention or plan.


In making places safer after dark, attention should be paid to how lighting can make a place more clearly visible and easier to navigate. This means that light should allow people to see changes in walking levels, materials, and other potential trip hazards. Light should also enable people to clearly see “conflict areas” where different users of the road and street come together (such as junctions and crossing points).

Nonetheless, highlighting these different components and areas of the urban fabric is not just about putting spotlights on them and turning the brightness up. For instance, illuminating surfaces vertically or integrating lighting into street furniture can be more effective than lighting from poles, as it can more clearly define the structure or object in question.

Generally, preventing excessive contrast and glare is a more important aid to visibility than the level of brightness. Human vision varies across individuals, but the range of light in which a healthy eye can see is very large, ranging from less than 1 lux under moonlight far from urban light pollution 8 through to bright sunlight at over 100,000 lux. 9

Crucially, however, it takes between 20 and 30 minutes for the eye to fully adapt to extreme changes in lighting. 10 This means that having extremely bright lights punctuating darkness at intervals can actually make it harder to see, as the greater contrast is more challenging for the eye. This is especially so for older people, as aging often means greater visual sensitivity to contrast. 11


The relationship between light and security is more complex. Both the likelihood of actual harm being caused by another person and one’s perception of this likelihood are the result of many different influences.

Establishing causal links between crime and discrete environmental and social influences is notoriously difficult and should be treated with caution. Studies exist showing a relationship between “improved” street lighting and reductions in crime, 12 yet there are also studies which show no such relation. 13 Such studies generally run up against the difficulty of isolating the impact of lighting interventions from other variables which can influence security. 14

It follows that we need to be cautious when making claims that changes in light will result in changes in social outcomes such as security. One fundamental misconception is that night-time is more dangerous than daytime. A review of the data shows that overall in 2018 there were more recorded crimes during the day than at night-time, 15 and almost 60 per cent of violent crimes against the person happen during the day. 16 However, the types of crime that take place can be different. Though only a small percentage of crimes take place at night, alcohol-related crime is more likely to happen at night, and is also more likely to involve violence or sexual crimes than non-alcohol related crime. Clearly the impacts of violent crime are far worse than the snatching of valuables. Overall, the evidence points to the complexity of the relationship between different types of harm, crime, and night and day.

We also need to consider the diversity of Londoners themselves. As with most aspects of urban life, our experiences and perceptions are shaped by a number of influences, with age, class, gender, geography, ethnicity and disability all playing a role.

There is strong evidence to show that night-time mobility is patterned by these characteristics, 7 so before we can consider the effects of a particular lighting intervention, we have to understand the range of factors that impact whether someone is on the street at night 18 and how they move around. We also know that different demographic groups are thereby more or less likely to be victims of violent crime, broadly defined. 19

Data from the GLA shows how different Londoners perceive their risk of harm at night. While 19 per cent of Londoners overall do not feel “safe” (here the word is used as in the original source, not solely in reference to accidental hazards) at night, this figure rises for women, people on low earnings, people with a disability, Londoners aged over 50, and Londoners aged 18-24. Those living in outer London boroughs also felt less safe at night than those living in inner London. Polling on this question did not record perceptions by ethnicity.

Perhaps related to their perceptions of security, Londoners rank lighting differently among night-time policy priorities. Overall, “better street lighting” ranks fourth on the list of priorities, after “more visible police in public”, “more free and low-cost activities”, and “improved nighttime public transport”. 20 But amongst older Londoners, Outer Londoners, disabled Londoners, women, and those in lower occupational grades, better street lighting is given a higher priority. 7 So better lighting can help respond to these perceptions, and enable more residents to participate in city life after dark.

Beyond headline demographic data, there are also other factors at play. In particular, site-specific factors play a large role in determining both the reality and perceptions of security in a place after dark.

For example, during research for this report we spoke with a researcher commissioned as part of a multidisciplinary team to investigate lighting as part of a public safety strategy in an outer London borough. They explained how the council had received requests for increased lighting in one area from local residents. When the team conducted in-depth interviews with residents in response, they found that the request for increased lighting had come from members of one ethnic group who were convinced of the criminality of another, and so were determined to use the lighting as a deterrent. Further, some members of a third ethnic group thought that both of the first two parties were equally the problem.

It is clear in this example that lighting provision in the area is not actually determining fear of crime: rather, it is the problematisation of different communities, and local tensions on the ground. Dealing effectively with these kinds of complex social situation will require more than a change in lighting colour, intensity and positioning. Community-led intelligence and data on how a place and its people interact can be far more useful.

The final point to note is regarding CCTV. Concerns over the ability of CCTV cameras to accurately capture faces can result in over-illumination. However, with a new generation of lighting technology, white lighting and better colour rendering can give clear CCTV footage without increasing overall levels of light too much.

As we have seen, there are a wide range of variables underlying the actual and perceived risk of harm from other people at night. If well-used, lighting can certainly be a tool to improve our experience of the city and reduce inequalities in the use of public space. But lighting should not be treated as the single factor that can determine security at night over and above all other influences at play.

Placemaking after dark

Beyond safety and security, lighting can also make London a more welcoming, accessible, equitable and enjoyable city.

The COVID-19 crisis is bringing new urgency to this agenda. Improving our ability to walk around the city at night, spend time in places and interact with each other could boost London’s economic recovery. In the commercial and cultural centres of our neighbourhoods, as well as the city centre, we should make use of every opportunity to support the vitality of London’s businesses and boost footfall. There is substantial evidence that increased footfall and improved pedestrian access to commercial areas can support profitability. 7

Night-time legibility

Being able to navigate the city after dark is related to one’s ability to “read” a place at night. We find our way in a city by orienting ourselves in relation to paths, intersections or landmarks – yet these are not always recognisable at night. 23 So lighting “the right places” – such as entrances, passageways or vistas – is at least as important as brightness in helping us navigate the city at night.

Using lighting to improve wayfinding seems logical, but it does mean focusing our attention on how people find their way on foot, rather than lighting the highway first so that cars can follow the road network. As such, it requires analysis and evidence gathering to learn how people use and navigate a space. Being mindful of mobility impairments is also important when considering navigation at this level of detail.

Enabling social interactions

The ability to recognise faces and expressions contributes to feeling secure when spending time outside at night. 24 Again, this is not a simple matter of more lighting being necessarily better. Where light is projected from has a great impact on readability – and even lamps with similar illuminance (the formal measure of the amount of light falling on a surface) can appear more or less bright, or show colours in a different way. 7

Who the lighting is attempting to illuminate is also important, as some types of lighting don’t work for all skin tones. This is increasingly recognised in photography, cinematography and the creative arts, but not yet in public lighting. If we want good lighting which enables all to see and be seen at night, we need to make sure that colour temperature and rendering are sympathetic to all skin tones.

Activation of a space

Another way that lighting can contribute to the quality of experience in a place after dark is through the activation of a space. A well-established principle of urban design is that having people actively using a space and interacting with each other encourages more people to use it and enhances feelings of security – a principle that the London Night Time Commission has supported. 26 The more people spend time in a place after dark, the more social, economic or cultural activity can take place there. Conversely, lighting can also “tell” us to be quiet: dimming or using lower-level lighting in residential areas at specific times would help keep noise levels down.

Here the quality of light is as important as its quantity and positioning. Lighting can make a place feel distinctive and valued, which can in turn increase feelings of security. 15

Of course, space activation can be a more challenging task, as cultivating an enhanced “mood” in a place requires the creative and aesthetic sensibilities of a good lighting designer. In the words of an experienced lighting designer: “Lighting is an art as well as a science”. 28 But lighting is also relatively easy to experiment with and adapt based on the public response – making it a quick and affordable way of shaping the look and feel of a space.

Public art

Last but not least, lighting can also be used as public art, to make the city more beautiful, playful and interesting. As set out above, light and darkness trigger deep responses, which is why many artists use light as their material. The combined use of light and sensors also offers huge opportunities for easy public interaction with the artwork.

Interventions can be as simple as helping us to appreciate our heritage after dark. This is well understood by organisations such as Historic England, which works to ensure that we can enjoy heritage buildings at night as well as in the daytime.

Lighting also has the potential to make us see our city differently by night than by day – and some uses of light serve precisely that purpose. The French city of Lyon hosts a renowned Festival of Lights which includes creative and colourful light projections onto the city’s building facades. In London, the Illuminated River project presented in the next chapter is transforming the Thames and the City at night by lighting its bridges.

Mood and wellbeing

Safety and security are not the only ways that lighting can impact our wellbeing. People’s visceral response to light and dark is no surprise when you consider that humans are a diurnal species, meaning we are typically active in the day and asleep at night. Human biology has evolved a finely-tuned network of systems which work according to our own internal clock – known as circadian rhythms. Light is a key moderator of our circadian rhythms, as our body intends to perform its waking functions in the daytime, when it is bright. Artificial lighting can extend the hours of brightness and expose us to stimuli that interfere with our natural bodily regulation. As such, the global adoption of electric lighting over the last 140 years also has a dark side.

Some of the impacts of excess (or insufficient) light on the body are well known, and the effect that blue light from smartphones and laptops can have in disrupting sleep is well documented. 29 In contrast, the phenomenon of Seasonal Affective Disorder (SAD) is linked to reduced exposure to daylight in the winter hours, and the NHS even prescribes light therapy as a treatment. 30 While it is inaccurate to reduce the complex interaction of multiple biological systems with light to simple mechanical inputs and outputs, lighting should be treated more seriously and sensitively as a potential environmental stressor.

This principle also holds true beyond simple biological responses. The relationship between wellbeing, mood and mental health is complex, but it is recognised that our local environment plays a key role. 31 Our environment in turn reflects and reproduces social forces. Having negative responses and stigma attached to a place has been associated with poor physical and mental health. 32

Lighting is no exception here. Research has shown that poor lighting is often installed in places that are assumed to be unsafe. 33 Harsh, forbidding light that dissuades people from spending time in a place can result in an intimidating, institutional feel, reinforcing the negative perceptions which informed the lighting in the first place. This approach is often used on housing estates, where floodlights can make spaces uninviting. By way of contrast, consider the relaxing and pleasant atmosphere of a walk through a sensitively lit conservation area at night – or think of the invitation to linger and explore that an artfully lit historic centre of a European city can offer. 34

Finally, good lighting supports our wellbeing by encouraging us to be active after dark – for instance by taking up physical activity or engaging in discussion with others. Making sure that all have access to quality of place at night matters.

The natural world

Human beings are not alone in being affected by light and dark. The rest of the natural world has evolved under the same natural lighting conditions as us. Assessing all the impacts of artificial lighting on the natural world would be an impossible task, but there are some key takeaways that we can consider.

One is that artificial light at night covers a substantial portion of the Earth’s surface. At the last count, this was close to 25 per cent. 35 Globally, it has been estimated that the percentage of the world experiencing direct light emissions at night is increasing by about two per cent every year, including an increase in brightness in already-lit areas. In heavily urbanised areas of the world, the coverage of light at night is far higher. Almost 90 per cent of Europe experiences light pollution at night, and North West Europe is particularly bright. 7 The most recent figures show that the UK’s night-time light coverage is increasing at around three per cent every year – faster than the global average. 37

This encroachment of artificial lighting denies us the romance and numinous beauty of a starry sky, or the otherworldly magic of a walk illuminated by moonlight. It is a loss, but one which must be balanced against the benefits that artificial lighting brings us.

Less well understood is the impact on wildlife. Much of the conversation in the UK has focused on bats, perhaps because they are a totemic nocturnal animal, charismatic and endangered – and hence subject to protection. There are documented negative impacts on bats from light pollution in some instances, including changes in normal movement patterns, disrupted hours of activity, and reduced reproductive success. 38 However, these vary across species of bats, and it is hard to disentangle some impacts of light from other areas of human intervention.

Looking at other organisms and habitats, a recent review of evidence finds that artificial lighting has observable impacts across a wide range of organisms – both diurnal and nocturnal. Artificial light has broad impacts on the creation of hormones (such as melatonin) that regulate sleep, on the behaviour of organisms which move towards light, and on their hours of daily activity. 39 There is less evidence overall of light-induced changes to the balance of different species, or total numbers of species in particular settings. Where this does happen, it is highly contingent on light’s impacts on particular key species or groups, which differ substantially. 7 Some places and systems will be more heavily impacted than others.

With wildlife as with human behaviour, accounting for this complexity means treating light with the attention and care it deserves. The range of psychological and physical impacts that artificial light can have are substantial and not to be dismissed. In each particular context and application, we cannot expect all potential impacts to be known in advance – but we can and should commit to asking the right questions if we are to mitigate the effects of over-lighting.

As we have seen, good lighting requires taking a broad range of considerations into account. The next chapter looks at how we make decisions on lighting.

  • 5 Ackroyd, P. (2012). London: The Concise Biography. London: Vintage.
  • 6 de Beer, E. S. (1941). The Early History of London Street Lighting. History, 25(100), March 1941, 311-324.
  • 7 Ibid.
  • 8 Kyba, C., Mohar, A., & Posch, T. (2017). How bright is moonlight? Astronomy & Geophysics, 58(1), 1st February 2017, 1.31-1.32.
  • 9 National Optical Astronomy Observatory (2015) Quality Lighting Teaching Kit, Recommended Light Levels. Retrieved from:
  • 10 Major, M. (2015). “London”, in Isenstadt, S., Petty, M. M., & Neumann, D. (eds.) Cities of Light: Two Centuries of Urban Illumination, 152-158. London: Routledge.
  • 11 Owsley, C. (2011). Aging and vision. Vision Research. 51(13), 1610-1622.
  • 12 Welsh, B. C., & Farrington D. P. (2008). Effects of improved street lighting on crime.
  • 13 Campbell Systematic Reviews. DOI:
  • 14 Perkins, C. et al. (2015). What is the effect of reduced street lighting on crime and road traffic injuries at night? A mixed-methods study. Public Health Research, 3(11). Retrieved from:
  • 15 Cozens, P. M., Saville, G., & Hillier, D. (2005). Crime prevention through environmental design (CPTED): a review and modern bibliography. Property Management, 23(5), 328-356.
  • 16 GLA Economics (2018). London at night: an evidence base for a 24-hour city. Retrieved from:
  • 17 Ibid.
  • 18 Transport for London (2019). Travel in London: Understanding our diverse communities. Retrieved from:
  • 19 Smeds, E., Robin, E., & McArthur, J. (2020). Night-time mobilities and (in)justice in London: Constructing mobile subjects and the politics of difference in policy-making. Journal of Transport Geography, 82.
  • 20 GLA Intelligence Unit (2018). Night Time Commission – Opinion Research. Headline Findings. Retrieved from:
  • 21 Ibid.
  • 22 Ibid.
  • 23 See Living Streets (2018). The Pedestrian Pound: The business case for better streets and places. Retrieved from:; and Transport for London (n.d.), Economic benefits of walking and cycling. Retrieved from:
  • 24 Institution of Lighting Professionals (2012). Professional Lighting Guide 03: Lighting for Subsidiary Roads. Retrieved from:
  • 25 Ibid.
  • 26 London Night Time Commission (2019). Think Night: London’s neighbourhoods from 6pm to 6am. London: Mayor of London. Retrieved from: sites/default/files/ntc_report_online.pdf
  • 27 Cozens, P. M., Saville, G., & Hillier, D. (2005). Crime prevention through environmental design (CPTED): a review and modern bibliography. Property Management, 23(5), 328-356.
  • 28 Major, M. (2015). “London”, in Isenstadt, S., Petty, M. M., & Neumann, D. (eds.) Cities of Light: Two Centuries of Urban Illumination, 154. London: Routledge.
  • 29 West, K. E. et al. (2011). Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans. Journal of Applied Physiology, 110(3), 619-26.
  • 30 NHS (2018). Overview: Seasonal Affective Disorder (SAD). Retrieved from:
  • 31 The Health Foundation (2018). What makes us healthy? An introduction to the social determinants of health. Retrieved from:
  • 32 National Institute for Health Research (2019). Area reputation and health inequalities – scoping the evidence. Retrieved from:
  • 33 Sloane, M., Slater, D., & Entwistle, J. (2016). Tackling social inequalities in public lighting. London: LSE. Retrieved from:
  • 34 Lighting Community International (2020). Exploring city nightscapes. Retrieved from:
  • 35 Falchi, F. et al. (2016). The new world atlas of artificial night sky brightness. Science Advances, 2(6). DOI: 10.1126/sciadv.1600377
  • 36 Ibid.
  • 37 Royal Commission on Environmental Pollution (2009). Artificial Light in the Environment. Retrieved from:
  • 38 Stone, E. L. (2013). Bats and lighting: Overview of current evidence and mitigation. Bristol: Bristol University. Retrieved from:
  • 39 Sanders, D. et al. (2020). A meta-analysis of biological impacts of artificial light at night. Nature Ecology & Evolution, 5, 74-81.
  • 40 Ibid.