Darker Cities due to the Energy Crisis and the need for context-specific urban lighting

Outdoor lighting has been dimmed or turned off in European municipalities due to the energy crisis. Dimming of outdoor lighting levels led to energy savings, advantages for biodiversity and less light pollution. But the dimming also triggers the basic human assumption that bright light is connected to safety and darkness is connected to fear. To discuss this basic assumption, human experience of dimmed lighting and perceived safety is explored through three case studies. One study explores human experiences of dimmed street lighting during energy crises, the second study investigates dimmed lighting levels around public transportation, and the third study is an example of a context-specific adaptation of street lighting in a residential area. The case studies reveal that dimmed lighting levels, minimized contrasts, and context-specific lighting can lead to an increased connectedness to the spatial and social urban context and an increased feeling of perceived safety. Thus, more light doesn’t always lead to more perceived safety. With a dimmed general lighting level, it is possible to introduce additional subtle lighting layers, structured in a lighting hierarchy to further enhance spatial and social qualities in outdoor contexts in the dark hours. in constructing both.


Introduction
In August 2022, energy prices in Europe rose to ten times the average from previous years [1].European municipalities therefore had to make decisions about how to lower energy consumption.Some municipalities lowered their energy consumption by dimming outdoor lighting, turning it off for selected periods of time or turning it off completely.However, dimming of outdoor lighting has both positive and negative consequences.The positive consequences of dimming lighting levels are not only energy savings, but also a reduction in light pollution [2], less circadian disruption for humans during nighttime [3], and better conditions for biodiversity in the dark hours [4].Furthermore, when the general lighting is dimmed, the lighting designer gets an opportunity to add subtle layers of lighting, which adds a spatial composition to the urban context which is related to social needs in the dark hours.
The negative consequences of dimming the outdoor lighting levels are mostly related to concerns in relation to crime, personal security, and traffic safety among local citizens [1].These concerns are often related to the basic assumption that bright light will reduce the risk of crime and increase f eelings of perceived safety, while darkness will increase a feeling of danger.This basic assumption is 1320 (2024) 012015 IOP Publishing doi:10.1088/1755-1315/1320/1/012015 2 based on culture and history, where darkness is often perceived as something negative [5].While the benefits of lighting are many, as Peter Boyce describes, we do need lighting to create perceived safety for pedestrians and traffic [6] [7].However, the need for lighting varies from place to place and general lighting regulations should be evaluated in relation to context-specific spatial and social needs.
Studies about perceived safety among women show that a higher lighting level is not always related to an increased feeling of safety [8].Likewise, other studies show that when lighting levels are lowered and balanced between lit zones and contrasts thereby are eliminated, surroundings and people become visible, and this leads to a feeling of safety [9] [10].To fully understand the complex connection between dimmed lighting and human experience of perceived safety, there is a need to further investigate the human and social dimension of lighting in the specific context that is being lit.To achieve more accessible, sociable, and sustainable cities, there is a need to investigate the nocturnal urban experience in terms of people's emotional, cognitive, and motivational perceptions [11].
The following three cases describe people's experience of dimmed and context-specific outdoor lighting in relation to three different types of outdoor lighting: 1) public roads, 2) public transportation and 3) local roads in a residential area.The three cases are chosen to discuss three types of areas where dimmed outdoor lighting affects the experience of outdoor areas.The basic assumption about dimmed lighting being related to an unsafe feeling is evaluated in the three cases to obtain a nuanced perspective on the positive and negative consequences of dimming the general lighting level in outdoor environments.
Case study one describes studies of people's experience of dimmed lighting in Copenhagen Municipality during the winter of 2022/23 [12] [13].Case study two describes people's experience of dimmed lighting around public transportation at a tram station in Aarhus, Denmark [10].Finally, case study three, describes how residents took an initiative to change the street lighting in their residential area of Humleby in Copenhagen.These three cases have been chosen because they concern dimming of urban lighting, and in two of the cases lighting has been adapted to context-specific conditions.The three case studies relate to a sustainable agenda, especially the UN Sustainable Development Goal 11.The dimmed and context-specific lighting can lead to inclusive, safe, and sustainable urbanization.Furthermore, case study three is an example of how a lighting project can be carried out, with participatory planning and management, to reduce environmental impact and secure an acceptance of the new design among locals in the residential area [14].Recent research shows that to ensure sustainable solutions in urban contexts it is necessary to co-design with local communities and ensure local participation in the process [15].By engaging local citizens when lighting is planned for their community, an ownership is developed in relation to the lighting design and to the neighbourhood [16] [17].Furthermore, by engaging locals, lighting can be carefully planned to live up to the Sustainable Development Goals in the dark hours and create urban environments that meet the UN target: 'Leave no one behind'.

Background
The general lighting level in lit urban zones is essential for how the urban space is experienced.If the lighting level is too high and contrasts are too large, our experience of the urban space can be destroyed in the dark hours.This can influence our feeling of safety.Contrasts in lighting levels can be between a lit object and the lit background [18] or contrast between two lit urban zones in the urban space [10].If contrasts in lighting levels are balanced and the general urban lighting level is dimmed, it becomes possible for the lighting designer to add subtle layers of lighting, planned in a lighting hierarchy according to context-specific spatial and social qualities in the specific urban space which is being lit.

Contrast in lighting levels between urban lit zones
To minimize contrast and create balanced brightness levels, it is crucial to create comfortable and safe urban spaces because the human eye is sensitive to light exposure.Therefore, when examining human experience of lighting levels in the urban environment, it is necessary to consider how human night vision functions.The human eye is sensitive to changes and requires time to adapt from one level of light to another.As an example, the human eye requires approximately 20-30 minutes to adjust from sunlight to darkness.The process of adjusting can be divided into three stages of sensitivity: photopic, mesopic, and scotopic vision.Photopic vision occurs when there is a luminance greater than 5 cd/m2.This allows for fine, detailed perception as well as colour perception.Scotopic vision occurs when luminance levels drop below 0,005 cd/ m2 and is characterized by an inability to perceive colours and a reduced ability to resolve details.The stage of sensitivity between photopic and scotopic vision is called mesopic vision, which occurs when luminance levels range between 0,005 and 5 cd/m2.Mesopic vision enables detail and colour perception when luminance levels are close to photopic vision; this ability is reduced as the luminance levels drop to the range close to scotopic vision [19] [20].
As the eye is very sensitive to changes in lighting levels, large contrasts in lighting levels should be avoided or designed with care.If, for example, a brightly lit commercial sign is placed in a dark spot, it will make the surroundings appear even darker.The contrast makes details, textures and shapes disappear.Bright light in shop windows or lighting on construction sites can also make large contrasts and make the surroundings look darker.Contrasts can also appear between lit urban zones with different activities or if one zone is brightly lit because the area is perceived as unsafe.But contrasts can make the space appear unsafe because the surroundings become invisible when the contrast is too high.Brighter is not always better, as Yang et al. claim when studying how women experience perceived safety in urban lit contexts [8].Lighting and darkness need to be balanced between lit zones [10]; when a general balanced layer of light is established, other layers of lighting can be added in a lighting hierarchy.To make the lighting hierarchy function optimally, it must be developed based on context-specific needs and spatial and social qualities [21].

Layers of Light
From the theatre, we know that lighting can produce any atmosphere needed to enhance the drama of the play, to direct the attention of the viewer or to provoke certain emotions [22].In architectural lighting design, some of the same principals of lighting are used, but there are limitations in practice that are not limitations in the theatre.The lighting designer Hervé Descottes refers to the 'instruments of lighting' when describing lighting characteristics, and he divides them into six principles of lighting: 1) illuminance, 2) luminance, 3) colour and temperature, 4) height, 5) density and 6) direction and distribution [23].These principles of lighting can be seen as different tools to create a lighting setting and need to be balanced to be able to distinguish the one from the other with the human eye.Together the principles represent layers of light in a lighting hierarchy.The lighting designer Richard Kelly worked with a lighting structure in his lighting design projects.He defined three layers of lighting needed to create a successful lighting design, where each layer of light has a role in the spatial composition.Kelly distinguishes between three kinds of lighting layers: 1) ambient luminescence, 2) focal glow and 3) play of brilliants.Through an interplay, the three layers need to be balanced to provide a perception of visual beauty [24].The ambient luminescence provides the general illumination of a space: it "makes surroundings safe and reassuring".The focal glow "makes it easier to see", the light is focused and conveys information about an object or a space to attract the viewers' attention.Finally, the play of brilliants "stimulates the spirit".Here, the light gives information or an experience.It "excites the optic nerves, and in turn stimulates the body and spirit, quickens the appetite, awakens curiosity, sharpens the wit.It is distracting or entertaining".These three layers of lighting need to be balanced and be a part of a holistic lighting design concept [24].For example, if the ambient layer of light is too high, it will not be possible for the human eye to see the play of brilliance.

Aim
Our night vision is sensitive to bright lighting levels and contrasts, as explained above.Therefore, it is important to lower and balance general lighting levels and add a variation of layers of light composed in a lighting hierarchy.
The aim of this paper is to explore, through three case studies: • if humans experience an urban space as safe in a lowered lighting setting, • if changes in contrast in lighting levels between urban lit zones make a difference in the perceived safety of those zones, • if an adaptation of the lighting to context-specific conditions can influence the human experience of an urban space.

Case studies
The outline of each case study is described in the following chapter: the methods used to explore the human experience of the changes in lighting levels and the result of each study are presented.

Case study one -Copenhagen municipality: human experience of dimmed lighting
In august 2022, the lighting department in Copenhagen Municipality planned a strategy for dimming urban lighting to ensure energy savings [13].The ideas for where and how to dim the lighting were discussed with the local police to make sure that lighting was not turned off in areas with high crime rates.Street lighting was dimmed 10%, effect lighting was turned off in most places (figure 1), and lighting was switched off between the hours of midnight and 5am in 25 parks.The Copenhagen Municipality lighting department only received a few complaints from citizens due to the changes in the outdoor lighting levels, and no complaints at all from the police.
Since 2009, the Copenhagen Municipality has each year made a 'Perceived Safety Investigation' to examine if Copenhagen citizens experience the city as secure and safe.Since 2020, the citizens' satisfaction with the lighting has been a part of these investigations, and in 2023 there has been a special focus on human experience of dimmed lighting levels [12].The company Epinion conducted this investigation for the Copenhagen Municipality and used both quantitative and qualitative methods to test how the savings on lighting in 2022/23 have affected Copenhagen citizens' perceived safety.The analyses in the report are based on responses from the last four years' perceived safety investigations in Copenhagen municipality (2020 to 2023).The database therefore consists of more than 13,000 questionnaire responses in the period spanning the past four years.Quantitative data sources from 2022-2023 consist of 6,000 questionnaire responses about citizens' experience of the lighting in their neighbourhood and their satisfaction with the lighting.This information is compiled with geographical data on the lighting in Copenhagen, including the city's light lines, light zones, and lighting systems, as well as data on the population composition and crime committed in the Copenhagen area.Qualitative data sources consist of a mobile ethnographic study among 22 female citizens, spread over six city districts.Over a period of two weeks, citizens have answered thematic tasks about their experience of safety and lighting in their district [12].
The results showed that most citizens found the lighting sufficient, although satisfaction varied from city district to city district.The lighting was experienced as good when it created a cozy atmosphere from different sources and levels.When there were too few light sources, too high contrast or the light became too warm in colour, the lighting was perceived as insufficient.When it came to the question of whether the savings on lighting in 2023 affected the security of the citizens, the result was that none of the citizens questioned had noticed the dimming of the street lighting.The dimming of the lighting level didn´t make the citizens less satisfied with the lighting and didn't lower the perceived safety of the citizens in the evening and night hours [12].

Case study two -Aarhus tram station: human experience of dimmed and balanced lighting.
Case study two represents an example of human experience of dimmed lighting at a tram station in Aarhus, Denmark.Studies were performed at tram stations to explore human perception of dimmed and balanced lighting in an urban social situation where people share an outdoor space and interact IOP Publishing doi:10.1088/1755-1315/1320/1/0120156 [10] [11].The intention of the studies was to explore how test participants experienced the tram station, the surroundings, people in the urban space, and the waiting activity at the station in two different lighting scenarios with different lighting levels.
The methods used were both quantitative and qualitative.Measurements were performed to define the lighting levels, and ethnographic methods were used to perform interviews.Experiences of lighting and darkness can be difficult for humans to describe as a vocabulary is lacking [25].Both measurements and interviews were performed first in the existing bright lighting setting, with a high contrast between the lighting level at the station and the lighting level in the surroundings.Secondly, the test participants experienced an approx.80% dimmed lighting setting, the lighting level now being balanced in relation to the lighting level in the surroundings.
The results indicated that a dimmed lighting setting created a more relaxed atmosphere at the station compared to the existing bright lighting setting.Furthermore, as it was possible to see people in the surroundings from the waiting area at the station in the dimmed lighting setting, the feeling of perceived safety and connectedness increased [10].The photos reveal the lighting settings and the influence the contrast in the lighting levels have in relation to the visibility of the surroundings.When the lighting level in the sheltered waiting area is dimmed, and the lighting doesn't reflect in the vertical glass surfaces, the surroundings then become more visible (figure 3) than in the bright lighting setting (figure 2).What are also revealed in the dimmed lighting setting are the commercials at the station and their very bright surfaces, which produce a high level of contrast.

Case study three -Humleby, context-specific street lighting in a residential area
Case study three is an example of how important context-specific lighting can be for a local community.Humleby is a residential area built in 1885 in Copenhagen.The residential area has a special character, and the residents were not satisfied with the glary street lighting that was installed by the municipality.Therefore, they spent two years planning how to change the street lighting into a lighting setting more suited to the context-specific character of the place.The lighting design project was carried out in collaboration with the lighting architect Gunvor Hansen and installation was financed by residents in Humleby and Copenhagen Municipality.
The problem with the street lighting was that the fixtures were positioned too high.This caused the lighting to come through the residents' windows.The lighting was too bright and had a cold colour temperature.In the new lighting solution carried out by lighting architect Gunvor Hansen, fixtures were positioned lower than before.A grid was positioned in the fixture to adapt the distribution of light to the design of the individual streets.Thereby, no spill-light came through the windows of the houses in the area.
The project is included in this paper as an example of a lighting project that was initiated and partly financed by residents in a housing area.A lighting designer was involved to ensure lighting quality and that all context-specific qualities were taken into consideration in the final lighting solution.It is an example of participatory design and how a local community can strengthen their sense of belonging in the local neighbourhood with the right lighting design for the dark hours.The photos illustrate how the street lighting lights up the facades and the spill-light coming through the windows before the position of the fixtures were lowered (figure 4).Subsequently, they illustrate how the street lighting only lights up the street, when positioned lower and a grid is installed in the fixture to direct the light (figure 5).

Discussions and findings
Before the energy crisis, legal requirements for lighting have been decisive, but now it has become necessary to circumvent this legislation, due to the need for energy savings.This change can give us valuable knowledge about how people experience dimmed lighting levels, and it can create the basis for new perspectives to the assumption that more light provides more perceived safety, and that darkness is experienced as unsafe.
The findings from case study one display that the test participants who were interviewed about the dimmed lighting in Copenhagen Municipality had not noticed the 10% dimming of the street lighting, and that the dimming had not lowered the feeling of safety.
In case study two, the dimming of the lighting was more significant.An approx.80% dimming of the lighting at a tram station in Aarhus, generated an unsafe feeling among 20% of the test participants.The remaining interviews showed that test participants had a positive experience of the dimmed lighting setting.They experienced that, when the lighting levels were balanced in the specific context and the contrast between lit zones disappeared, it was possible to see the surrounding space and people.This led to an increased feeling of connectedness to the place and an increased feeling of safety.
Case study three is an example from praxis, an example of how a few changes in the design of a lighting solution can have a great impact.The amount of lighting was reduced, and the improved lighting setting added quality to the experience of the neighbourhood in the dark hours instead of a lighting solution that caused contrast and inconvenience to the residents living in the area.
It is important to recognize that there is a need for using both qualitative and quantitative methods to research human experience of outdoor lighting.Legal requirements are primarily based on a tradition of quantitative research [8]; however, there is a need to create awareness among decision makers about the spatial and social potentials of lighting in urban environments.There is also a need to discuss lighting levels in relation to the risks that we as humans experience in outdoor environments: including the risks of being involved in an accident and the risks of being a victim of violence or threats.It has been found that for pedestrians, the risk of being a victim of a crime is what people fear the most [26].
During the field experiment at Nørreport tram station in Aarhus, even though the tram passes very close to where one waits for the tram, only a few test participants mentioned the fear of being involved in an accident [10].During the design process, the fear of accidents and the fact that the tram driver could be glared by the lighting on the station and therefore not be able to see the people waiting, was the parameter that was discussed the most, according to Holscher Design, and not the fear of crime.
Studies from Melbourne University [8] concerning the relationship between urban lighting and perceived safety also show that brighter lighting is not always related to a higher degree of perceived safety.Likewise, their results reveal that when contrast-ratio is unbalanced, pedestrians tend to feel unsafe.These studies also investigated other lighting parameters, such as colour temperature, colour rendering and uniformity in urban lit contexts to look for connections between perceived safety and lighting parameters.
The dimming of lighting due to the energy crises has revealed that in many cases lighting can be dimmed without reducing perceived safety.When the general lighting levels are dimmed, this leaves room for introducing subtle layers of lighting in outdoor environments, which can create inviting and safe places for urban citizens.

Conclusion
The three case studies show that it is possible to dim the general lighting and create more value.It is not in all places that it is necessary to add extra layers of light to highlight the character of the place, sometimes it is 'just' the right distribution and balance between lighting and darkness, which can make a difference and lead to better lighting solutions."Too much light wipes away the sense of place", as the architect Juhani Pallasmaa describes [27].The sense of specific places, i.e., their context-specific spatial and social qualities, are necessary to take into consideration when a lighting solution is planned in the urban context.
The results from the three case studies have led to three concluding findings, which can be considered in future urban lighting design solutions: A. Lighting Hierarchy: dimming of general lighting levels and supplementing with layers of light in a lighting hierarchy will make the space inviting, safe and sustainable and ensure that context-specific spatial and social qualities are enhanced.All three case studies reveal that it is possible to lower lighting levels and still establish safe and inviting outdoor environments.Case study one, lowered street lighting, case study two lowered lighting around public transportation and case study three lowered lighting levels in housing areas.The lowered general lighting levels allow for subtle layers of lighting in outdoor environment.A lighting hierarchy can be established which enhances social interaction, draws attention to context-specific qualities or activities can be established.
B. Balanced Brightness Levels: consider balanced brightness levels in the general lighting.With a balanced brightness level between lit zones, the local space and the surroundings, a holistic lighting design can be established.
Case study two demonstrates how high contrasts in lighting levels in an outdoor environment can create the experience of dark areas.While when lowering and balancing lighting levels a safe and inviting outdoor environment can be established.
C. Context-Specific Lighting: enhance spatial and social qualities.Context-specific lighting should be developed and co-designed with the citizens living in the area, hereby ensuring social and sustainable solutions.Case study three is an example of how a local community took the initiative to change the street lighting in their neighbourhood.The new contextspecific lighting in Humleby is an example of how a few adjustments can create a solution where lighting is only where it is needed.