Spatial planning for dark hours in Sweden – conditions and proposal for action

The purpose of this study was to investigate how the absence of daylight are handled within spatial planning in Sweden, and to propose measures for action. The study includes a review of spatial planning documents, interviews with planning officers, and an overview of how outdoor lighting is included within the Swedish Planning and Building Act (PBL). The result shows that planning documents according to the PBL generally present few specific analyses and proposals linking to the design and the use of outdoor environments during dark hours, such as lighting. Instead, outdoor lighting is often managed within lighting masterplans, that lack a common methodology and a formal planning status. Possible consequences include that spatial planning provides limited support for how different public interests should be weighed against each other in a nocturnal context, and that citizens have little formal influence over strategic decisions on outdoor lighting. As a proposal, we suggest developing spatial planning for dark hours (‘nattstadsplanering’ in Swedish), that integrates the use, the design, and the outdoor lighting within the same planning process, using the PBL as a framework. The proposal includes clarification of lighting regulations, methodology development, and knowledge dissemination, which requires further research and investigations.


Introduction
When night falls and daylight disappears, the use and the character of the outdoor environment change in a profound way.Most living species are biologically adapted to the regular light and dark patterns, that emerge from the rotating earth, and are either diurnal or nocturnal.As humans are diurnal, we generally spend most of our awake time in daylight, but ever since the invention of electric lighting, society has undergone a temporal revolution and is now active 24-hours-a-day [1].Outdoor lighting has made public spaces accessible and populated during dark hours and has large benefits for the individual and for the society [2].The extensive use of outdoor lighting [3], also has multiple negative impacts, including astronomical and ecological light pollution and impacts on humans, in terms of health and obtrusive light [4].Societies located in high latitudes, that are characterized by strong variation in daylength during different seasons of the year, such as Sweden, are especially depending on outdoor lighting.In December, the number of dark hours per day (sunset-sunrise) last around seventeen hours in the south of Sweden (Malmö) and twenty-four hours in the north (Kiruna).The light conditions at high latitudes dissolve the connection between the astronomical definition of 'night', when the sun is below the horizon, and the temporal definition of 'night', for example between 22-06 [5].The lack of daylight affects the use of public spaces.For example, in subarctic areas, darkness is seen as one of the most important climatic barriers for walking outside [6], and due to unsafety, many women avoid certain areas and means of transportation during dark hours [7].Furthermore, the experience of the townscape and the landscape alters completely, when the light from the sun and the bright sky is replaced by the dark vault of the night sky, with its subtle moonlight and starlight, and the layer of electric lighting.Through the quality and the quantity of light, in relation to the surroundings, outdoor lighting changes the character and the ambiance of the nocturnal city [8].The illumination of the city could be used to underline the interplay and the relationality between light and darkness, and to embrace them both [9].

Spatial planning for dark hours in Sweden
The background to this study, is that we, in our professions within architecture, urban planning and lighting design, have reflected on the idea that the daily shift from day to night should be considered more within spatial planning, to ensure that public spaces are well-designed and sustainable throughout the day and night.Within this study, we reflect on the concept of 'spatial planning for dark hours' ('nattstadsplanering' in Swedish), that should be seen as a perspective on urban spatial planning that considers the specific conditions that occur when there is no daylight.According to our definition, spatial planning for dark hours includes both the use, the design, and the lighting of the outdoor environment.In this context, 'night', 'night-time', 'nocturnal' and 'dark hours', refer to the astronomical night, i.e., the absence of daylight, regardless the time of day.A similar approach to urban planning, that focuses on a certain temporal or seasonal change, can be found within the concept of winter urban planning [10,11].In this study, we have used Sweden as a case study, to examine how the absence of daylight is handled within urban spatial planning, and if the national planning framework within the Swedish planning and building legislation (PBL) [12], could form the basis for spatial planning for dark hours in Sweden.

Research questions
The following research questions have been addressed: • In what way are the special conditions during dark hours, including outdoor lighting, managed within spatial planning according to the PBL, and within lighting masterplans?• Does spatial planning according to the PBL, and lighting masterplanning, consider relevant public interests for dark hours?Does the planning process provide citizens, authorities, and stakeholders the possibility to influence the night character of the outdoor environment?• How is outdoor lighting included within the PBL legislation?Could existing tools and processes within PBL form the basis for spatial planning for dark hours?

Limitations
This study has been carried out with the ambition to identify tendencies and possibilities as a basis for further research development.Even if there is other relevant legislation, this study focuses on legislation within the PBL.The research material, in forms of interviews and planning documents, is dated before 2017, when a new ordinance on building permission for light source facilities was adopted.

Relevant tools and processes within the PBL
To identify relevant tools and processes for spatial planning for dark hours, we have reviewed the PBL legislation with a focus on outdoor lighting.The review has included the Swedish Planning and Building Act and the Planning and Building Ordinance [12], relevant mandatory provisions and general recommendations from the Swedish National Board of Housing, Building and Planning [13,14,15,16], including relevant guidance on the legislation [17,18,19].

Public interests
The PBL [12] describes public interests that should be considered within all spatial planning.Regarding outdoor lighting, it follows from Chapter 2, Section 6, that light source facilities must be designed and placed in a manner that is suitable with regard to certain public interests.In addition, it follows from Chapter 2, Section 9, that outdoor lighting may not be located, placed, or designed so that the intended use could result in the impairment of the surroundings that would entail a danger to people's health and safety, or cause significant negative impact in any other way.Pursuing to the PBL [12], conflicts between different public interests must be consciously weighed against each other in an open and democratic planning process, considering the rights of individuals.In this study, a selection of public interests that are specifically affected by the presence or absence of daylight is summarized (figure 1).
Figure 1.Selection of public interests, specifically relevant for spatial planning for dark hours.In comparison to the PBL, some public interests have been reformulated and grouped by the authors.

Planning system
Pursuant to the PBL, the Swedish planning system, consists of spatial plans of different kinds (figure 2) [12,19].All planning documents within the PBL are generally subject for consultation, exhibition and review by the public, relevant authorities, and other stakeholders.
In the comprehensive plan, the municipality presents how the built environment should be used, developed, and preserved, including public interest considerations.The comprehensive plan is not legally binding but gives guidance for detailed planning and building permits.The comprehensive plan may be amended regarding a particular part of the municipality (amendment) or a particular public interest (addendum).On a regional level, the County Administrative Boards are responsible for planning material and supervision of national interests.Within this study, we have not found any guidance on how dark hours, including outdoor lighting, could be managed within comprehensive planning.
Within detailed development plans, the municipality regulates the use and the design of the built environment within certain geographical areas.The detailed development plan may not be more detailed than needed to fulfil the purpose of the plan.It follows from the PBL, Chapter 4, Section 12, that the detailed development plan can be used to determine maximum permissible values for disturbance through light, if there are special reasons [12].Within a detailed development plan, the municipality may also decide on exemptions from building permit requirements for light source facilities.Within valuable environments, building permit requirements for outdoor lighting may also be extended, using provisions in detailed development plans or area regulations [12,17,18].However, the guidance on provisions from the Swedish National Board of Housing, Building and Planning, gives limited support regarding outdoor lighting, bringing up the possibility without providing concrete examples [18].Regarding building permits, The PBL legislation valid until 2017 stated that light source facilities require a building permit within areas covered by a detailed development plan [20].Legal practice from earlier legislation has stated that normal street lighting does not require a building permit [17].In 2017, an amended ordinance clarified that a building permit is required for light source facilities within an area covered by a detailed development plan if i) 'the intended use may have a significant impact on the surrounding', or ii) 'it is placed on or adjacent to a building or a development area that is particularly valuable from a historical, cultural, environmental, or artistic point of view' [12,17].According to the Swedish National Board of Housing, Building and Planning, there are uncertainties in how to interpret the legislation [17].Light source facilities that require a building permit must demonstrate a good effect of design, colour, and material and may not be distorting [12].
Planning material and programmes, such as aesthetic design programmes, can be annexes to all spatial plans according to the PBL, and can be used to provide more detailed guidelines, for example regarding design principles.The municipalities can also develop other types of planning documents, such as policies, strategies, programmes, and guidance on different topics, that are not connected to the PBL spatial planning system.Lighting masterplans are generally developed within this category.

Methods
To analyze how the special conditions during dark hours, including outdoor lighting, are managed within spatial planning, we have interviewed urban planners and building permit officers in different municipalities.We have also reviewed a selection of planning documents according to the PBL, as well as a selection of lighting masterplans (table 1).Qualitative research methods have been used.The selection of municipalities has been made with the ambition to cover a spread of geographical locations and population sizes.The municipalities in the interview series were partly selected based on our knowledge that they had a certain interest or experience in planning for dark hours in some ways.The three most populated municipalities in Sweden have been excluded from the study, since we judged that they have special planning conditions.The identity of the municipalities, the respondents, the spatial plans, and the lighting masterplans are withheld for confidentiality reasons.

Interview series with urban planners and building permit officers
The interview series consisted of separate, individual phone interviews, that were carried out during 2015-2016.The ten respondents worked as urban planners or building permit officers at urban planning departments in nine different municipalities (table 1).The interview questions focused on how they plan for the special situations that occur during dark hours (table 2).In the interview, we asked for the respondents' opinions and professional experience within the municipality where they were based.The interviews were semi-structured, using yes and no questions, that were followed up with questions where the respondent could answer in an explanatory descriptive way, as a basis for conversation.The interviews were documented by notes.4 If planning for the special conditions during dark hours, including lighting, involved internal or external participation, and if so, in which stage of the planning process and with whom.

5
The respondent's interest in methodological support within spatial planning for dark hours.

Document review of planning documents according to the PBL
The document review included a selection of spatial plans, annexes and building permits (table 1), covering all municipal spatial planning levels according to the PBL, except for area regulations (figure 1).In this study, these are all referred to as 'planning documents according to the PBL'.The planning documents were selected and provided by the respondents in the interview series.The respondents had an explicit ambition to share material that they judged relevant for the study.Respondents from three of the municipalities chose not to share any planning documents, since they judged that they had no relevant spatial plans or building permits within their municipality.The documents were asked to have become legally binding between 2010−2015.Two of the detailed development plans in the study were adopted before 2010 but were important to review because they regulated the building permits included in the review.The review of the detailed development plans included the legal documents of regulation and recommendation (plan map and planning description), as well as aesthetic design programmes, that were carried out as annexes.As a research method, we have screened the spatial plans for selected words related to the 'dark hour perspective', including outdoor lighting.

Document review of lighting masterplans
The document review included lighting masterplans on both municipal and city district scale, from twelve municipalities (table 1).The selection of lighting masterplans has been based on internet search on the word for 'lighting program/plan/strategy/policy/guidelines' (in Swedish).In this paper, all these documents are referred to as lighting masterplans.The plans were dated between 2009−2015 and covered a spread of different consultant firms that had been engaged in the document development.
Consultant firms in which we had been employed ourselves, at the time of the document review, were excluded.The content of the lighting masterplans was divided into five categories (table 3).The sitespecific or specific lighting guidelines were divided into four detail levels (table 4).To review in what way the lighting masterplans considered public interests, we analyzed how a selection of related themes, such as 'natural values', 'light pollution', 'obtrusive light', 'biodiversity', 'cultural values/heritage', 'façade lighting', 'safety', 'accessibility', 'traffic environment', 'energy use' and 'economy', were managed within the plans.To analyze whether there was a common terminology and methodology, the document's titles and contents were compared.We also reviewed which representative bodies that had adopted the lighting masterplans and if the lighting masterplans had been subject for consultation.Guidelines using qualitative characteristics to describe how something specific should be illuminated.3 Guidelines using quantitative characteristics to describe how something should be illuminated.4 Guidelines that present a clear lighting principle of how something specific should be illuminated.

Spatial planning according to the PBL
In the interview series, the urban planners and the building permit officers explained that they consider the special conditions that occur during dark hours in their spatial planning in general, especially regarding safety and design.One example that was brought up in the interviews was that buildings were designed and located so that paths would be active and populated throughout the day and night.Most of the respondents thought that it is relevant and possible to manage the special conditions that occur during dark hours within spatial planning according to the PBL.Aesthetic design programmes, that are annexes to the spatial plans, were evaluated as the most adequate planning form to describe lighting principles within spatial planning according to the PBL.Several respondents considered that it, in some situations, could be relevant to regulate outdoor lighting in detailed development plans and building permits, but expressed an uncertainty about how the PBL should be interpreted regarding lighting regulations.The interviews clearly showed that the respondents interpreted the legal support for lighting regulations within the PBL in different ways.Many of the respondents requested methodology support on how to express lighting guidelines and regulations in spatial plans and building permits.They also requested clear guidance on how to interpret the PBL, as well as the Swedish Environmental Code [21], regarding lighting regulations.
The review of the planning documents according to the PBL showed that when the 'dark hour perspective' was taken into consideration, it was primarily on a general level, and rarely in connection to specific proposals.Proposals for outdoor lighting were more often described in the annexes.

Lighting masterplanning
In the interview series, the municipalities expressed a general need to plan outdoor lighting for larger areas.Almost all respondents had developed, or were developing, a lighting masterplan for either the entire municipality or for specific districts or sites.Most of the lighting masterplans that were reviewed within this study had been developed with the support of external consultants.
The review of lighting masterplans revealed that the plans lacked a common terminology, methodology and detail level.The content of the lighting masterplans that covered an entire municipality were often similar and on a general level.The lighting masterplans that covered one or several city districts generally contained more site-specific planning materials and guidelines, which had a wide spread of detail levels.The differences in content and detail level did not correspond to differences in document titles.Almost all lighting masterplans focused on the municipal's main city.
Only two out of sixteen lighting masterplans mentioned that certain lighting principles (façade lighting) could require a building permit.

Public interests
The review of the planning documents according to the PBL showed that when the 'dark hour perspective', including outdoor lighting, was considered in relation to public interests, it was most often highlighted in connection to safety.Some isolated proposals on how to reduce negative environmental impact from outdoor lighting were found within the planning documents.
The review of the lighting masterplans showed that traffic environment, safety, cultural heritage, façade lighting and energy use, were central themes within most of the plans.The lighting masterplans on a city district scale generally considered the themes in a more site-specific way, including more analysis and proposals, in comparison to the lighting masterplans on a municipal scale.Negative impacts from outdoor lighting were brought up on a general level by almost all lighting masterplans on a municipal scale, but by only half of the lighting masterplans on a city district scale.Site-specific or quantitative guidelines on how to limit negative effects from outdoor lighting were rarely included in any of the plans.

Democratic influence
The PBL provides citizens, authorities, and stakeholders opportunities to gain transparency and influence throughout the spatial planning process.Usually, it is also clear which representative body within the municipality is responsible for decision-making.The review of planning documents according to the PBL indicated that lighting proposals were rarely presented.The review of lighting masterplans showed that only one of the plans stated that it had been subject for consultation.The review also showed that the lighting masterplans had been adopted by various representative bodies.

Discussion
The result indicates that municipalities consider the special conditions that occur during dark hours within their spatial planning in general, but that the 'dark hour perspective', including lighting proposals, is rarely presented within planning documents according to the PBL.Instead, strategic lighting planning is often managed within lighting masterplans that lack a common methodology and a formal status, not linked to the PBL.Other studies confirm a lack of established common terms, definitions, and methods for lighting masterplanning [22,23].Especially, we have found limited guidance on lighting planning as an integrated part of urban spatial planning.For example, CIE [24] points out the importance of stakeholder inclusion and suggests lighting masterplans to be an essential part of the wider urban plan.However, they provide limited support on relevant processes.A reason could be that the planning and building legislation differs between countries, which underlines the importance of national guidance.
This study also indicates that spatial planning generally provides limited support for how different public interests should be weighed against each other in a nocturnal context.Since lighting masterplanning generally focuses on the municipality's main city, the lack of guidance is most significant for smaller villages, as well as rural and natural areas.Negative aspects of outdoor lighting, such as ecological and astronomical light pollution, were generally addressed to a lower extent than, for example, safety and traffic environments.However, it is important to note that both research and general awareness regarding light pollution and the need of darkness have increased since the planning documents within this study were produced.The increased awareness can be noticed within more recent Swedish lighting masterplans, that address light pollution and darkness to a higher extent.Another example is that several detailed development plans in Sweden have been appealed due to the risk that the planned buildings could harm habitats for bats, that are nocturnal and legally protected [25].
Since lighting proposals are rarely included in the planning documents according to the PBL, and lighting masterplans are rarely subject for public consultation, the result of this study indicates that citizens generally have a little formal influence over strategic decision on outdoor lighting.
This study also shows that the PBL offers many existing tools and processes relevant for spatial planning for dark hours.Several benefits of using the PBL as a framework for spatial planning for dark hours could be identified.To plan the use, the design, and the lighting of the built environment within the same process, and to treat lighting as one architectural tool among others, would support important public interests, such as aesthetic design and a favourable overall impression.In addition, the PBL provides the possibility to limit negative effects from outdoor lighting.The selection of public interests relevant for spatial planning for dark hours (figure 1), has several correlations with key aspects of sustainable urban lighting, identified by Zielinska-Dabkowska [26, p.25-26].Also, the PBL planning process would ensure that public interests are considered and weighed against each other, and that citizens, authorities and stakeholders would be given the opportunity to influence during the planning process.Another benefit is that building on and implementing established tools and processes, would gain an equivalent management, and support interdisciplinary cooperations.
However, there is no established methodology or guidance for how the 'dark hour perspective', including outdoor lighting, could be addressed within spatial planning according to the PBL.An important obstacle is the uncertainty of how the legislation concerning lighting regulations should be interpreted and implemented.Even if legislation for building permits for light source facilities have been updated since the research material in this study was conducted, uncertainties remain [17].Different interpretations of the legislation may lead to an undesirable diversity between municipalities.

Proposals
To promote well-designed and sustainable outdoor environments throughout the day and night, we propose to develop spatial planning for dark hours ('nattstadsplanering' in Swedish), focusing on public interests, the use, and the experience of nocturnal outdoor environments.Our proposal is that spatial planning for dark hours should be based on tools and processes within the PBL.When possible and relevant, the planning for dark hours should be integrated within the regular spatial planning, as a perspective on the overall planning situation.For a successful development and implementation, we propose the following measures of action, that include further research and investigations.

Clarification of the legal basis for lighting regulation
To be practically applicable, we propose that the legal basis for lighting regulations through building permits and provisions should be evaluated and clarified, both within and outside valuable areas.It should be clear which kind of outdoor lighting that may require a building permit since it 'may have a significant impact on the surroundings', or, since 'it is placed on or adjacent to a building or a development area that is particularly valuable'.Guidance is also needed regarding which planning material within comprehensive plans, detailed development plans and programmes, could support the municipality's examination of permits, as well as provisions in the plan map.As a response to the important sustainability challenge of light pollution, we propose to evaluate if and how building permits for light source facilities could form the basis for national and local regulations against obtrusive light and to protect the cultural and natural values of the night sky.Further research and investigations are needed to define which kind of lighting 'may have a significant impact on the surroundings' in this regard.As reference, the guide on the limitation of obtrusive light from the CIE [27] and the French legislation for the limitation of light nuisances [28] include different quantitative thresholds for outdoor lighting for different types of area.

Methodology development
We propose that methods for spatial planning for dark hours should be developed for all planning levels according to the PBL (figure 2).The different planning levels ensure a process from comprehensive to detailed spatial planning for dark hours and allow municipalities to adapt their planning to local conditions.The methodology development needs to include relevant definitions to support a common terminology.Tools for analysis and proposals should be developed with adequate detail levels, following the formal status of both guiding and legally binding spatial plans.The development of spatial planning for dark hours within comprehensive planning should focus on long-term guidance that provides the basis for more detailed planning, including building permits.The 'dark hour perspective' should, when relevant, be included within strategies for sustainable development and public interest considerations.We suggest that comprehensive planning could be used to describe the intended use and the desired characteristics of the townscape and the landscape during dark hours.This could include strategic guidance on the quality and quantity of outdoor lighting, including guidance on the limitation on obtrusive light within different areas.Comprehensive planning could also be used to give guidance on within which situations lighting regulation could be used to protect valuable environments.On a regional level, the County Administrative Boards should support the municipalities with planning material regarding the development and the protection of cultural and natural values connected to dark hours.Regional collaboration for comprehensive spatial planning for dark hours could be relevant for municipalities with similar nocturnal conditions.
The development of spatial planning for dark hours within detailed planning should focus on descriptions of how the area is intended to be used and experienced during dark hours.As a perspective on the overall design, the design of outdoor lighting should be included, in relation to public interests such as safety, townscape, cultural and natural values, and the limitations of obtrusive light.The methodology development should provide guidance on how lighting proposals can be expressed within the plan, including how provisions for the lighting can be used to ensure important values.The methodology needs to consider that detailed development plans are valid for a long period of time, while IOP Publishing doi:10.1088/1755-1315/1320/1/01201410 lighting technologies and knowledge evolve continuously.The methods also need to consider that the detailed development plan may not be more detailed than necessary.
We conclude that aesthetic design programmes, that are annexes to spatial plans according to the PBL, are an adequate planning form to describe more detailed design proposals, including lighting.We propose that lighting masterplans could be developed as annexes to spatial plans according to the PBL, giving them the same status as aesthetic design programmes.
Methods for spatial planning for dark hours should also be developed for situations where there is no ongoing planning according to the PBL.To meet the definition of spatial planning for dark hours, these plans (spatial plans for dark hours and lighting masterplans) would need to consider relevant planning material, site-specific public interests and be subject for a democratic planning process.

Dissemination of knowledge
When relevant lighting legislation has been clarified and adequate methodologies for spatial planning for dark hours have been developed, we propose that a broad knowledge dissemination should be conducted.The knowledge dissemination should include a national guidance, providing basic knowledge about light and the role of outdoor lighting in relation to public interests, as well as a summary of relevant legislation, adequate methodologies, and good practice for spatial planning for dark hours and lighting masterplanning.We propose that the Swedish National Board of Housing, Building and Planning should be responsible for national guidance and coordination.Together with regional support from the County Administrative Boards, national guidance would relieve each municipality to compile general lighting knowledge and practice, and free up resources for site-specific planning.

Conclusion
Within this study, the concept of spatial planning for dark hours ('nattstadsplanering' in Swedish) has been elaborated, with Sweden as a case study.According to our definition, spatial planning for dark hours includes both the use, the design, and the lighting of the built environment, and weighs relevant public interests against each other within a democratic and transparent process.After interviewing urban planners and reviewing planning documents and national guidance on planning and building legislation, we can conclude that there is no current, adequate methodology for how the 'dark hour perspective', including outdoor lighting, could be managed within urban spatial planning.However, we have identified many relevant tools and processes within the PBL that could be developed and applied.For a successful development, we highlight three key proposals, including legal clarifications on lighting regulations, methodology development, and knowledge dissemination.We believe that these steps will support sustainable and well-designed outdoor environments for nocturnal situations.

Figure 2 .
Figure 2. Overview of regional and municipal planning in Sweden.

Figure 3 .
Figure 3. Examples of relevant planning tools on a municipal scale: (a) shows guidance on obtrusive light [29], including environmental lighting zones according to the CIE [27], (b) shows guidance on development of dark infrastructure [adapted from 29], c) shows guidance on building permits for lighting, describing areas with high cultural values and areas covered by a detailed development plan.Illustrations by C Fraenkel.Published by courtesy of Nacka kommun and White arkitekter.

Figure 4 .
Figure 4. Example of relevant planning tools on a city district scale: (a) shows Lynch's five elements for analyzing a city [30] with a 'light and dark perspective' proposed by the authors, (b-c) show plans describing the structure of lighting and darkness on different times (for example evening/night or summer/winter).Illustrations by C Fraenkel.

Table 1 .
Municipalities and research material included in the study

Table 2 .
Summary of interview questions.
1If and how the special conditions during dark hours, including lighting, is managed within the municipal spatial planning practice in general.2Ifandhow the municipality manages the 'dark hour perspective', including lighting, within plans and documents that are not in accordance with the PBL's spatial planning system.3If and how the municipality manages the 'dark hour perspective', including lighting, within spatial plans and building permits in accordance with the PBL, and if lighting is subject for regulations.

Table 3 .
Content categories within the lighting masterplans.

Table 4 .
Detail levels of guidelines and proposals within the lighting masterplans.