Lighting for critical conversational environments: A scoping review

Abstract

Little is known about the impact of lighting in rooms designated for critical conversations in counselling or policing contexts, such as therapy, clinical interviewing and police interviews. Lighting may affect bodily stress, discomfort, nervousness, anxiety, mood and self-disclosure. The aim of this study was to map and report research on how illumination affects people’s perception, mood and interaction in healthcare and policing contexts. A scoping review was conducted in which six databases were searched. Twelve studies were included: ten quantitative, one qualitative and one mixed method. The results were presented in two overarching categories: impact of lighting on communication and behaviour. The first category consisted of four sub-categories. The second main category depicted methods and experimental design. The findings indicate that this specific area remains relatively under-researched. The studies were mostly experimental and consisted of small samples. An improved understanding of lighting in contexts for critical and personal dialogue can support professionals, patients and organisations, not least in psychiatric healthcare and other socially vulnerable settings. In addition, our results may inform future design intervention studies and the configuration of rooms designated for conversational and policing environments where critical conversations are conducted.

1. Introduction

1.1 Rooms for conversation and interrogation

This scoping review focuses on lighting in settings where personal and critical conversations take place, specifically within healthcare environments and police interrogation rooms. Critical conversations are understood as sensitive personal dialogues that may be experienced as uncomfortable and emotionally challenging. The conversation room in healthcare environments and the interrogation room share spatial and relational similarities, typically in the arrangement where two (or more) individuals interact. In interrogation settings, the individuals generally face one another directly, whereas in the conversation room, there is greater flexibility in terms of proximity and facial orientation, allowing for regulation of interpersonal distance and gaze. In interrogation rooms, lighting fixtures are commonly integrated into walls or ceilings to prevent their use as harmful objects, reflecting a design focus on control and safety. While both spaces are shaped by asymmetric power relations, the intended beneficiary differs. In the therapeutic conversation room (hereafter referred to as the conversation room), the vulnerable and intended beneficiary is typically the patient. The person being interrogated, by contrast, is usually in a more constrained and vulnerable position. In both environments, the distribution of power is unequal in relation to control over the physical setting, including ownership of space and light, both in a literal and emotional sense.

This scoping review was conducted by a multidisciplinary research group with backgrounds in lighting, design, architecture, healthcare environments and criminology. The review is guided by a focus on theoretical perspectives on the interaction between light, physical space and conversation in therapeutic and policing contexts.

1.2 Previous research

Previous research has seldom focused on light distribution in relation to spatial experience and atmosphere. However, lighting design pioneers Flynn, Spencer and Martiniuk^2–4 found that people prefer spaces with illuminated walls and tend to turn towards them. They also found that an atmosphere of intimacy or privacy could be created with low-intensity lighting near the observer, combined with varying light patterns placed higher and further away, preferably with more wall-oriented lighting. When vertical lighting was combined with warm-white lighting, it created a spatial experience of relaxation. More intense lighting was associated with emotions of activity and efficiency. ⁵ In addition, brightness contrast was found to play an important role in sustaining visual attention. ⁶ Flynn’s experiments have been repeated with similar findings. ⁷ The importance of vertical lighting for catching visual interest has also been reported by Loe, Mansfield, Rowlands and McIntosh.^8,9 These findings are now included in guidelines for office work. ¹⁰

The spatial experience can be more important than we realise, and vertical lighting reinforces the spatial boundaries. Hesselgren^11,12 and Dalkvist and Gärling ¹³ found that the light level is crucial for the experience of being enveloped by a space. In their experimental studies, spatial enclosedness increased with the light level up to 100 lx, but it decreased when the light level was too high. In addition to wall-oriented lighting, the directionality of light also matters. In an experimental study conducted in an auditorium, it was found that the directionality of light, in combination with the light distribution and the light level, impacted whether the audience felt invited to participate in a discussion. Light can therefore also be understood as a tool for creating more or less democratic social situations. ¹⁴ Furthermore, Wänström et al. ¹⁴ found that interviewees lowered their voices and listened more intensely when the room was darker. Moreover, Sanders et al. ¹⁵ found a relationship between nonuniform lighting, low light levels and voice volume. Light patterns also contribute to spatial experience. Madsen ¹⁶ studied light zones in daylit rooms and defined them as being separated, connected or overlapping. Lindh^17–19 further developed Madsen’s light-zone concept and found that light zones can be experienced together as a pattern, contributing to the room’s perceived width, height or depth. Very large spaces can trigger a sense of exposure and aloneness, whereas cramped spaces may trigger a fight-or-flight-reaction, which is deeply rooted in our neurological system.^20–22 It has also been found that light zones can impact people’s experiences of being enclosed or excluded from a lit room. ¹⁴

Studies of atmosphere and mood are commonly based on colour temperatures and light levels.^23–25 Most studies on room atmosphere have been performed in retail environments.^26–29 General studies on atmosphere and light distribution are less common. However, the vast majority of lighting designers apply Kelly’s ³⁰ three main principles for creating spatial atmosphere: focal glow, ambient luminescence and a play of brilliants; these principles are based on variations of light distribution. Stidsen et al.^31,32 investigated the light atmosphere in hospital wards with a focus on light distribution and suggested that hospital care spaces should be designed with three zones in mind: the patient zone, the care zone and the visitor zone.

Facial expression and eye contact are vital for the outcome of a conversation. Vertical lighting from above, which creates hard shadows, may contribute to an intimidating facial impression, whereas softer contrasts and a warmer light, reflecting from the sides, can create a friendlier and softer impression. How light illuminates a face is highly important, as shadows can either make facial expressions and emotions easier to interpret or distort our perception of a person’s state of mind.^33,34

In interrogation rooms, as in any environment for critical discussion and investigative interviews, materiality, colour, light and the interior configuration play a crucial role. Kassin et al. ³⁵ discuss the risk of false confessions in police interrogations and refer to Inbau et al., ³⁶ stating that placing people in a ‘…small, bare, windowless, soundproofed room, seated in a hard-back chair’ is recommended for confrontational approaches. This description of the environment aligns with common cultural representations, particularly in black-and-white films, of suspects being interrogated in stark, windowless rooms illuminated by harsh overhead lights. The former archetypal environment aligns with Inbau’s ³⁶ recommendation that ‘diffused, overhead lighting is more appropriate’ for interrogation rooms. However, creating these harsh environments may be only one part of a cluster of factors that create ‘situational risk factors’ pushing individuals towards false confessions. ³⁵ On the other hand, some of the literature discusses how people’s perceptions of a certain style of room can impact the situation; if the idea of the ‘hard architecture’ ³⁷ is not met, it can affect both the interviewer and the interviewee in different ways. ³⁸

1.3 The effect of lighting on conversation

Carr and Dabbs ³⁹ studied the impact of verbal disclosure and eye contact in dim or bright light, and at near and far distances between an interviewer and an interviewee when discussing intimate questions (sexuality). They found that eye contact decreased and that people took more pauses in their speech (latency to talk) in dim lighting. Participants perceived the dim lighting as very intimate, but inappropriate for the task. Gifford ⁴⁰ studied the effect of light level (dim vs. bright) and home décor on interpersonal communication when paired participants sitting face-to-face silently wrote letters to each other. Brighter lighting stimulated more general communication (both general and intimate). Lower lighting was associated with more intimate communication, but over time, lower light levels dampened all forms of communication. Gifford focused solely on light level and did not explore other lighting aspects, such as light distribution. Baron et al. ⁴¹ investigated illuminance and colour temperature. In dim lighting, participants appraised a fictive employee as having higher performance than in bright lighting. Participants exposed to warm-white lighting showed stronger preferences for resolving interpersonal conflicts. When participants received a small gift (candy) in warm-white, low lighting, their willingness to donate increased, compared to bright lighting. Miwa and Hanyu ⁴² found that dim lighting (as opposed to bright lighting) increased participants’ self-disclosure. Their dim lighting increased feelings of relaxation and pleasantness. It also induced a favourable impression of the interviewer and increased speaking time. It is unusual for studies to focus on light distribution in rooms in relation to atmosphere. Still, this was the primary focus of a study in a group therapy room at a psychiatric hospital. Mathiasen et al. ⁴³ tested two different light distributions: one using ordinary tubular luminaire lighting with a character of general lighting (3000 K), illuminating a large part of the room, compared with pendant lighting over the table (2700 K). Naturally, more aspects than light distribution differed; the colour temperature and uniformity also shifted. The patients in the study preferred the low-positioned lighting over the table, which they described as pleasant, relaxing, cosy and homelike, while the general lighting scenario was described as institutional.

It is not just lighting that impacts room perception. Patterns, colours and materials also impact spaces, sometimes regardless of the lighting and sometimes together with the lighting. A horizontal pattern may widen the impression of the room, and a vertical pattern may increase the perceived room height.^17,18,44 Earlier research has found that furnished rooms feel smaller than unfurnished rooms, but half-furnished rooms feel larger than both furnished and unfurnished rooms.^22,45

1.4 Theoretical approaches

This review intertwines two theoretical perspectives: caring and policing. Taking on a caring perspective, place and space are understood not only as physical phenomena, but as something that we live through our bodies, where, among other factors, light level, light distribution and colours shape space as it becomes place. The perception of spatial dimensions can be altered through lighting levels on surfaces, which creates patterns, contributing to the impression of spaces within a space.^14,17,18 The concept of space has two meanings; on one hand, it deals with the physical place, not necessarily, but often delimited by four walls. However, a space is constituted by the meanings that people ascribe to a place. ⁴⁶ Lefebvre ⁴⁷ describes the experienced space, which, without physical walls, can also be experienced as a tangible spatial unit.^47,48 A place can also be defined by its location and its reputation as a landmark in people’s consciousness, that is, a socially constructed place. ⁴⁹

Disclosing, confessing or opening up are desired actions in the context of the physical environments. One way to understand the role of the physical environment in supporting such actions is that the dedicated room, whether an interrogation room or a therapy room, shall provide affordances^50,51 that support the human senses and nervous system in the action of disclosing. The design of the physical environment can either increase or decrease people’s stress levels. ⁵² However, there appear to be differing views on whether increased stress reactions, as an effect of the design of the interrogation room, are desirable or not.^35,38

In the policing context, the design of interrogation rooms influences the overall experience for both the interrogators and the interrogated suspects or witnesses. In interrogations, the literature discusses the necessity of altering physical space, so-called context manipulation, to influence both comfort and to maintain control and power dynamics. ⁵³ In addition, traditional interrogation techniques of suspects are designed to create a sense of surprise and confusion, which can have long-term psychological effects. This highlights the necessity of considering the intersection between the psychological impact of lighting design and interrogation methods. ⁵⁴

Evidence-based design (EBD) is a methodology that integrates research findings into the design process to improve outcomes. ⁵² The design should balance functionality with aesthetics to create a comfortable and engaging environment. In healthcare settings, evidence-based modifications have led to improved scores in room atmosphere and safety, by reducing stress and promoting well-being. ⁵⁵ Key design features in EBD include a user-centred approach, functional and/or aesthetic enhancements and empirical validation. In addition, EBD aims to minimise physical and psychological barriers to communication. ⁵⁶ While EBD has been extensively applied in healthcare settings, its principles can also be adapted to other forms of conversational rooms to enhance user experience and functionality. In conclusion, environmental factors have been emphasised as important within EBD, particularly light, lighting and spatial design, which can also be linked to stress and, in turn, influence human behaviour.

In a caring context, the counselling and therapy room is regarded as central to creating a safe and protected environment in which the client or patient can feel comfortable opening up. In both therapy and counselling, it is common for clients to experience vulnerability when sharing thoughts and emotions, which underscores the need for comforting, homelike environments.^42,57 Control over the environment, such as the ability to choose where to sit, what to face, or the amount of exposure to light, has also been identified as an important factor in promoting comfort and a sense of safety.^3,58,59 Similarly, therapists express a need for control, as the therapy room functions not only as a space for critical conversations but also as a professional work environment. Creating an environment that is comfortable for professionals is also crucial, as dissatisfaction with the physical setting may indirectly influence their behaviour towards clients. ⁵⁸

In therapeutic alliances and encounters in the context of caring and intimate critical conversations, personal disclosure may be at stake. According to Logstrup ⁶⁰ and Martinsen, ⁶¹ there are always active power structures in such meetings. The interplay between the individuals and how power is exercised that shapes the outcome of the meeting. Therefore, it is of interest how lighting may impact such meetings.

1.5 Rationale

The relationship between light and darkness is complex. Light makes things visible, gives information and provides visual guidance so we can orient ourselves in spaces and places. Darkness, on the other hand, can provide a feeling of being in a refuge, protected, excluded or invisible. There is little research on atmosphere and spatial experiences in relation to light. The research is predominantly limited within a quantitative paradigm.^43,62 The focus of the current study is on how light affects the dynamic relationship between the two communicating participants in contexts for closed and/or critical conversations, particularly in enclosed spaces and places designed for sensitive and intimate conversations. With more knowledge in this area, it will be easier to design lighting in a room that promotes comfort, encourages openness and facilitates self-disclosure. Therefore, this scoping review aims to map and report research on how illumination affects people’s perception, mood and interaction in spaces. To exemplify, this can be a room for critical conversations held in a healthcare context, such as therapy or interrogation. Such conversations are often characterised by unequal power relations. The following research questions have guided our study:

1. What conclusions can be drawn from the included studies that have relevance for lighting design for conversation rooms?

2. How does lighting affect behaviour, mood and interaction in caring and policing contexts?

3. What methods and study approaches have been used in the selected dataset?

2. Method

This scoping review maps the extent and content of research published in the above-described research area and provides a foundation for future research studies. Scoping reviews are suitable methods for exploring current knowledge, especially in an inter- and transdisciplinary field.^63–65 The review comprises all aspects of how lighting affects the experienced spatial atmosphere, including light level, light distribution and spectral distribution.

2.1 Review method

This scoping review followed the framework established by Arksey and O’Malley, ¹ which consists of five steps: (1) identification of the research problem, (2) identifying and selecting relevant studies, (3) charting data, (4) extracting and (5) summarising and reporting the findings. Moreover, the reporting of the search process was guided by the PRISMA ⁶⁶ protocol, and the quality of the included studies was appraised using Hawker et al.’s tool. ⁶⁷ This has facilitated consistent assessment across qualitative, quantitative and mixed-methods research.

2.2 Identifying and selecting relevant studies

The structure of Population, Exposure, Outcome (PEO) was used to construct a search string, define inclusion criteria and guide the search and selection process. MeSH terms and CINAHL headings were used to ensure the identification of adequate search terms. Based on the PEO structure, three primary concept blocks were developed (Table 1).

Table 1

The PEO structure and related search terms

The PEO structure	Related search terms
Population (1) (People)	B1 People (18 terms): Patient–Physician Interaction, Physician–Patient interaction, Patient–Psychiatrist, Professional client relations, Client relations, Therapeutic alliance, Conversation partners, Conversation leader, Interrogator, Investigator, Interlocutor, Dialogue partner, Discussion leader, Conversation leader, Facilitator–respondent, Patient–therapist, Patient–psychologist
Exposure (2) (Lighting)	B2a Lighting (8 terms): Light*, Illumination, Lighting design, Light planning, Light ergonomics, Light environment, Light architecture, Visual comfort B2b Type of lighting/Light quality (7 terms): Light level, Light distribution, Light colour, Colour temperature, Brightness, Lightness, Illuminance, Luminance
Outcome (3) (Environment)	B3a Meeting (16 terms): Caring encounter, Therapeutic environment, Interrogation, Investigation, Meeting B3b Behaviour (8 terms): Talking, Conversation, Therapy, Question, Answer, Speaking volume, Listening, Seating, Sitting, Interacting, Taking initiative, Body language, Posture, Attitude B3c Place (12 terms): Room, Conversation room, Environment, Hospital, Detention B3d Atmosphere (13 terms): Atmosphere, Spatial atmosphere, Human atmosphere, Emotion

In total, 82 distinct search terms and combinations were used to operationalise the PEO components (see Supplemental Material). A comprehensive literature search was conducted systematically across six databases (CINAHL, ProQuest Central, PubMed, PsycINFO, Scopus and Web of Science) using a combination of MeSH terms and free-text searches in titles and abstracts, together with two of university librarians. The search was structured into three blocks and combined with a Boolean operation. The complete search string consisted of keywords presented by the PEO structure, blocks 1, 2 and 3 (Table 1) and was applied to all databases. Rayyan was used to screen the selected papers, filtering for exclusion criteria that might have been missed in the initial screening (Table 2).

Table 2

Overview of inclusion and exclusion criteria

Purpose	Criteria
Inclusion	• Peer reviewed • Published between: 2009 and 2024 • English or Nordic language • Main focus on experiences of lighting or illumination • Care or interrogation environment • Therapy/consultation rooms • Secluded rooms • Interactions between individuals
Exclusion	• Reviews or conference papers • Grey literature • Light therapy or cyclic light • Paediatric context • Virtual reality • Telemedicine • Daylight • No social interactions • Physiological responses

2.3 Relevance screening

Finally, a total of 1804 papers were imported into Rayyan, a tool for literature review and screening (https://www.rayyan.ai/) ⁶⁸ . We did not use the built-in AI function. The papers were divided into four groups (n = 451) and screened by two researchers per group based on titles and abstracts. To increase validity, the references were screened by the authors interchangeably in various constellations. During this initial screening stage, 1766 papers were excluded (Figure 1). Most exclusions were due to the terms light or illumination being used metaphorically rather than in their literal sense, for example, in phrases like ‘shedding light on an issue’, ‘illuminating a problem’ or ‘highlighting a topic’. Additionally, many papers did not involve actual social interactions and were therefore excluded as they fell outside the scope of this study. Therefore, two additional searches were conducted. Firstly, a manual search was conducted in which the authors handpicked suitable papers from the following journals: Lighting Research and Technology, Leukos, HERD, Counselling and Psychotherapy Research, Journal of Environmental Psychology, Environment and Behaviour, Clinical Psychology and Psychology Research.

Figure 1

The PRISMA 2020 flow diagram, showing the search process

Secondly, an AI-assisted search was performed using Research Rabbit, a search tool that combines snowballing and pearl-growing strategies to identify related papers based on the key studies (https://www.researchrabbit.ai/). A selection of publications from the initial search, along with background papers, was used to conduct the Research Rabbit search. Following the screening of titles, abstracts and full texts, a total of 12 relevant papers were included in the dataset for the final analysis (Figure 1).

2.4 Data-charting process and quality screening

A quality assessment was performed on the selected papers; they were read in full and evaluated using the pre-defined criteria described by Hawker et al. ⁶⁷ The 12 included papers were assessed concerning their relevance to the research questions and methodological quality. Through Hawker’s appraisal tool, each paper was independently evaluated across the nine domains, including sampling, data analysis and ethics, and each domain was rated on a four-point scale from good, fair, poor, to very poor (Appendix 1).

Although quality assessment is not a required component of scoping reviews, it was conducted to provide additional context regarding the robustness of the existing evidence. The appraisals were compared and discussed in the research group to ensure consistency and rigour in the quality evaluation process. All included studies were assessed independently, by at least two researchers.

2.5 Extraction of the data

The extraction of the data was conducted according to the practical/pragmatic approach proposed by Popenoe et al. ⁶⁹ Extracted data were organised into a matrix summarising each study’s design, population and main findings. The following areas were also identified in each study: the type of the environment, experimental design or surveys with photos, context, type of activity, description of the lighting conditions (temperature, colour, window), conclusions related to the light/illumination, the composition of the research group and drawings of the room layout/blueprint (Appendix 1). Ten studies were quantitative, one qualitative and one was performed within a mixed-methods design.

2.6 Analysis of the data

Each paper was summarised by two authors, according to the description by Hawker et al. ⁶⁷ We identified topics and sorted them into sub-categories and categories. Tables were used for thematic sorting according to Popenoe et al.’s ⁶⁹ description. Based on our research questions, key contents were tabulated for analysis (Appendix 1). Examples of the identified themes include experimental lighting set-ups (e.g. bright vs. dim) in relation to spectral or light distribution, context of the meeting, spatial context, experimental procedures, study participants and methodological approaches. Some themes are more descriptive, while others are more abstract, such as different types of meetings. Within each theme (e.g. bright vs. dim lighting), the findings were organised according to similarities and differences.

3. Results: Impact of lighting on communication and behaviour

3.1 Contexts in the dataset

The majority of the selected 12 papers presented quantitative experiments in laboratory environments, predominantly conducted in Europe (see Appendices 1 and 2). In the selected studies, different forms of meetings are addressed; these differences also create different conditions for meetings in relation to lighting. However, the conditions for the meeting situations vary between involuntary and voluntary meetings. In addition, the degree of interaction may vary depending on which hierarchical structures are active in the room and on different power relationships.

Although we systematically searched several databases for papers specifically addressing lighting in policing contexts, there was a clear absence of such studies compared to the caring context. As a result, only 1 of the 12 papers included in the dataset was conducted in a policing environment.

3.2 Light levels

Most studies focused on light levels in terms of bright–dim. Some papers dealt with light and colour aspects, and a few mentioned other aspects such as daylight, decoration and furnishing (Appendix 3).

Ru et al. ⁷⁰ found that bright light increased self-control and satisfaction, and decreased perceived anonymity. They further suggested that bright light can promote prosocial behaviour. Similarly, Steidle and Werthe ⁷¹ described that a brighter room was associated with higher self-awareness and self-regulation. According to Ishikawa and Kasumi, ⁷² dim lighting, in turn, was perceived as friendlier and more relaxing. Speaking times were longer with shorter pauses, and the distance to the interviewer was assessed as shorter. Participants also leaned forward towards each other. Excessively high light levels can be counterproductive, according to Cui et al., ⁷³ who found that the emotions of a patient peak at 200 lx, but at higher light levels, the emotional factor decreases. When using a picture inquiry, Okken’s ⁷⁴ research team detected a link between threatening situations, brightness and perceived spaciousness. When a threatening situation occurred (e.g. a message of a diagnosis), participants perceived the room as more spacious with increased brightness.

3.3 Spectral distribution

Regarding spectral distribution, Davis et al. ⁷⁵ concluded that coloured light had a positive effect on concentration and productivity. Cui et al. ⁷³ found that nurses prefer a higher colour temperature, compared to patients who prefer a warmer, lower colour temperature. In line with Cui et al.’s results, ⁷³ Sinclair ⁷⁶ describe how therapists and clients, rated lighting and feelings about lighting slightly differently. These groups had somewhat different priorities, with therapists to a greater extent emphasising the importance of being able to control the lighting, whereas client’s priority was that clinical rooms with bright lighting were unwelcoming.

However, Mehta et al. ⁷⁷ found that it was difficult to measure disclosure in relation to environmental lighting. Kuijsters et al. ⁷⁸ connected different colour temperatures to emotional responses in terms of cosiness and anxiety. Their study included not only different colour temperatures but also varying light distribution and light levels in different parts of the room, and their cosy scenario was found to reduce anxiety, while the positive mood scenario increased participants’ willingness to talk.

3.4 Interior and furnishing

There were studies that combined brightness variables with different levels of decoration and furnishing. For example, Davis et al. ⁷⁵ showed that coloured light had a positive effect on concentration and productivity. Moreover, Hoogesteyn et al. ⁷⁹ noted that the decorative interrogation room was assessed as more homelike and relaxing; it included floor lamps and table lamps, while the other scenario only had general lighting from the ceiling. Sanders and Lehman ⁸⁰ used qualitative methods, letting patients furnish their ideal therapy room. They described the importance of natural light from windows, which opened up and brightened the room.

3.5 Meeting context, mood and behaviour

Not all studies explicitly discussed meetings and conversations per se (Appendix 3). However, they emphasised the effect that lighting and the physical environment had on mood, self-awareness, disclosure and emotional regulation, factors that are crucial for the outcome of any meeting in which a critical conversation takes place. The types of meetings discussed in four of the studies can be grouped into three categories: interviews (Ishikawa and Kasumi), ⁷² investigative interviews (Hoogesteyn et al.) ⁷⁹ and counselling conversations with a therapist.^76,80 The remaining studies focused primarily on self-disclosure or mood, but not necessarily within the context of meeting another person. Moreover, it is notable that all reviewed studies were conducted in constructed laboratory settings and did not contain data from real meeting contexts.

In six studies, the individuals’ handling of a meeting, in terms of behaviour or self-disclosure, was the main subject. Behaviour was included in studies on social and cognitive behaviour, ⁷² impulsive behaviour, ⁷¹ peripheral activity awareness ⁷⁵ and altruism. ⁷⁰ Self-disclosure was the main subject in two studies: Mehta et al.’s study ⁷⁷ on self-disclosure and Hoogesteyn et al.’s study ⁷⁹ on police interviews. Counselling or therapeutic meetings were addressed in three studies: Sanders and Lehmann’s, ⁸⁰ Sinclair’s ⁷⁶ and Okken et al.’s. ⁷⁴ Care situations were addressed two studies. One of them focused on lighting to improve the mood in the elderly, ⁸¹ and the second examined the emotional and visual effects of the luminous environment of a cardiac ICU on both patients and nurses. ⁷³ Only one study included both young and elderly participants for studying low- or high-arousal ambience, ⁸¹ which can be seen as important for all the above studies.

3.6 Methods and experimental design

Ten of the included studies employed an experimental design and followed a theoretically driven, quantitative approach to test hypotheses (Appendix 2). They focused on measurable outcomes and statistical analysis in their efforts to verify or falsify the hypotheses of their studies. Nevertheless, in most of the studies, the cohorts were relatively small and primarily consisted of university students or people of a young age.^{70–72,74,75} The data collection was primarily based on self-assessment or surveys, both based on Likert scales.^{71,74,75,77,79}

In addition, photos and written reflections were collected from participants, who were encouraged to cognitively imagine and evoke different feelings (trust, fear, etc.) in relation to different lighting setups.^74,78,82 In general, the studies relied on similar statistical methods, using non-parametric or parametric tests such as ANOVA, t-tests and the Mann–Whitney U-test. However, regardless of the choice of statistical method, the studies assumed that self-assessment data could be treated as ordinal data and that the data always met the standardised data distribution requirements: normal distribution for parametric tests and non-normal distribution for non-parametric tests (Appendix 1). No discussion was presented to the readers on the appropriateness of applying parametric methods to ordinal data. Moreover, the limitations sections lacked depth and critical reflection on the fact that many studies did not consider light level and colour temperature, two vital aspects in lighting research. Finally, the only qualitative study ⁸⁰ used semi-structured interviews and co-creation, whereas the mixed-methods study ⁷⁶ used survey data.

Several studies claimed to investigate a single lighting variable, yet their experimental setups differed on more than two dimensions without explicitly acknowledging this (Appendix 3). For example, studies that examined differences in light level (bright vs. dim) also varied in light distribution, luminaire placement and spectral distribution. This concerns Mehta et al., ⁷⁷ who compared general ceiling lighting with the light from a single compact fluorescent lamp. Similarly, Hoogesteyn et al. ⁷⁹ compared two scenarios, one decorative and one simpler, but the lighting conditions were not directly comparable. The decorative room included a greater number of luminaires, including floor and table lamps, whereas the standard interview room relied solely on general ceiling-mounted lighting. The same imbalance can be found in older studies by Gifford ⁴⁰ and Carr and Dabbs, ³⁹ who both used ceiling light for the bright scenario, but a table lamp for the dim scenario. In contrast, studies that identified light distribution as the primary variable differed in other respects between scenarios, such as uniformity and spectral distribution. ⁴³ However, these authors explicitly intended to study a complex room environment and did not claim that the two scenarios were fully comparable; rather, light distribution was presented as the dominant variable.

4. Discussion

To sum up, all studies applied their chosen methodology adequately, but there seems to be a lack of both large-scale quantitative studies and qualitative studies regarding the experience of lighting in social situations.

4.1 Reflections on the findings

The 12 papers in our review followed previous research in both focus and experimental set-up. Dim–bright studies of a conversation situation have previously been carried out by several research groups.^39,40,42 Only a few of the previous studies have studied illuminance in relation to colour. ⁴¹ None of the selected papers focused on light distribution, but a few of the papers that built up the background section of this study did.^31,32,43 Surprisingly, light distribution has not been the focus of more studies, since light variations and shadows are the aspects that create and emphasise spatial boundaries in the room.^21,83 Ceiling light is used in most studies. Most papers referred to the studies by Flynn et al. ² They show that light distribution (a low-placed light source and peripheral wall lighting) has a large effect on the experience of a room as intimate and private. Several studies showed differences in light distribution, but none discussed the topic. It is only recently that differences in light distribution, as in Flynn’s study, have been tested in a conversation study in a healthcare environment. ⁴³ The reason why earlier research has been so focused on light levels and overlooked other aspects is discussed by Mathiasen et al. ⁴³ Light levels are the only guidance that is clearly specified in the international lighting standards. ¹⁰ Most of the researchers in the current dataset were psychologists rather than lighting researchers. More lighting knowledge is likely needed to be able to consider other aspects beyond the light level. Today’s equipment, with LED light sources and programming of light scenarios, provides increased opportunities for creating experimental set-ups that can be varied across comparable scenarios. We also have better equipment for measuring light distribution with luminance photos. Overall, light level is easy to measure and instruments are inexpensive, but a luminance camera remains prohibitively expensive. With current LED light sources, we also have more possibilities to control complex lighting scenarios.

Several of the papers studied self-disclosure, self-awareness, self-control, self-confidence or perceived anonymity.^70,71 These themes are also found in the older papers.^40,42 Dim lighting is described as promoting personal and intimate conversations, while bright lighting is beneficial for general conversations. In a conversation session, it could be an advantage to be able to remain more anonymous, partially concealed by dim lighting. If you want people to disclose more personal information, it is beneficial that they feel anonymous. Sometimes dim lighting feels safer, but if a person is not acquainted with the therapist, s/he may feel unsafe meeting in dim lighting. Overall, dim lighting seems to have been more appreciated and beneficial for sensitive and open conversations in both newer and older studies.^39,42,72,73 Dim lighting was also associated with a more positive impression of the conversation partner in older papers.^41–43 However, Gifford ⁴⁰ found that dim lighting over time had a declining effect on communication. The findings of Cui et al., ⁷³ that there can be a threshold when a room becomes too bright, align with Hesselgren’s study,^11,12 where spatial enclosedness decreased with brighter light. This is also in line with Okken et al.’s ⁷⁴ results that brightness was linked to spaciousness and anxiety. Kuijsters et al. ⁷⁸ also found a relationship between lighting and anxiety. Patients and staff may have different preferences for lighting ⁷³ ; nurses may relate to work lighting, while patients refer to their home environment. Mathiasen et al. ⁴³ described that bright light was associated with institutions.

4.2 Limitations and review method reflection

As stated earlier, the research group in the current study has expertise in healthcare environments, policing contexts and interior and lighting design, and represents knowledge within both the qualitative and quantitative paradigms. This background, together with the group’s aim to develop future interventions related to police interrogation settings, motivated the database search in the policing context, despite the limited findings. With this research gap identified, the motivation to continue lighting research in these contexts is strengthened. Both contexts, therapy and policing, relate to each other within a broader caring perspective, where the boundaries between care and custody are closely intertwined.

The database search was based on keywords, abstracts and titles. The nine papers that were found by handpicking did not meet the formulated PEO requirement and were therefore not detected by our database search. In the handpicked papers, either light or space-related terms were missing in KEY-ABS-TITLE, but the content was covered in the full papers. Some papers did not use terms related to room or space in the title, abstract or keywords.^{70,71–73,75,77} However, other handpicked papers lacked lighting-related concepts.^76,80,82 Therefore, authors of scientific papers need to be more careful about finding keywords. Perhaps we could have covered even more keywords in our own search, or truncated the search concept environment* to also capture the concept environmental? Other search concepts that appeared in the papers’ keywords that we did not search for include self-disclosure, self-awareness, self-regulation and self-control, terms that are apparently central. We did not search for counselling, interviews or psychological distance. We searched for ambiance (-s)”, but not for ambient, which should also have been truncated.

It was difficult to find the right combinations of search terms. As an example, the term physician–patient relations produced over 30 000 hits in medical databases such as CINAHL, Scopus and PsycINFO, but fewer than 2000 in Web of Science and ProQuest Central. In contrast, the terms patient–psychiatrist relation and psychiatrist–patient relation produced no more than 72 hits in any database. The term client relations yielded between 1500 and 6000 hits in Scopus, Web of Science and ProQuest Central, but only 22 to 633 hits in the medically oriented databases.

5. Conclusion

Most studies focused on light levels, while colour aspects and light distributions were less researched. The atmosphere created in a room depends on a complex relationship between light, colour, material, texture and furnishings. Meetings in rooms for critical conversations tend to involve hierarchical power relationships. The lighting design can either support or hinder an equal relationship between both parties. When the lighting supports a sense of homeliness and comfort, it benefits self-disclosure. According to the current dataset, bright light is beneficial for increased self-control, self-awareness and self-regulation, and it decreases anonymity. On the other hand, dim light can increase relaxation, shorten distance between people and increase speaking time. Coloured light in combination with dim lighting can have an effect on the willingness to talk; it can also affect the experience of cosiness, which may relate to reduced anxiety. Light distribution is apparently an under-research area. The studies in the dataset displayed different samples and different contexts. Despite these limitations in sample diversity and size, the authors of the studies often claimed that their findings were broadly generalisable to a wider population. Therefore, we recommend a more stringent design with larger samples that can be compared to each other. In addition, more studies performed within a qualitative perspective are needed, as lighting itself is related to lived experiences. Moreover, design principles and techniques for interrogation rooms can benefit from integrating the EBD principles for healthcare settings, since they promote a sense of safety and comfort, without reducing the sense of security and improving the overall experience for both staff and subjects.^84,85

Finally, the findings of this review may also be informative for other conversational settings beyond the scope of the present study, such as employment interviews or salary negotiations.

From this perspective, there are some implications for future research which we want to highlight:

• Further methodological development may be beneficial for the field, as several studies appear to replicate earlier designs rather than explore alternative approaches.

• There seems to be a need for additional research examining spatial light distribution in rooms.

• The complexity of the room environment, including colours, contrasts, materials and furnishings, may benefit from greater consideration.

• Investigating complex environments with multiple interacting variables could offer valuable insights, although such approaches may require qualitative or mixed-methods designs.

• Research on lighting in interrogation rooms remains limited, suggesting a potential area for future studies.

Supplemental Material

sj-pdf-1-lrt-10.1177_14771535261434525 – Supplemental material for Lighting for critical conversational environments: A scoping review

Supplemental material, sj-pdf-1-lrt-10.1177_14771535261434525 for Lighting for critical conversational environments: A scoping review by U Wänström Lindh, C Thodelius, B Lindahl, S Olausson and F James in Lighting Research & Technology