Uniform vs. uneven lighting: Accommodation of multiple users’ preferences in study rooms

Uniform lighting in public spaces like study rooms in libraries, is still a common practice. However, uniformly lit spaces are unable to simultaneously meet the needs of multiple users and can create dull environments. The objective of this research is to analyze users’ behavior under different lighting conditions in study rooms and investigate whether alternative lighting designs, which step away from uniformity, could be more beneficial than uniform lighting, from a human performance and well-being perspective. A uniformly lit study room in the library of KTH was chosen as the main case study of this investigation and was thoroughly analyzed and evaluated through qualitative and quantitative research. Under the initial hypothesis that the lighting in this study room does not meet its users’ needs and fails to create an inspiring and comfortable environment, three additional study rooms in different Swedish libraries were comparatively analyzed through observations, interviews, and questionnaires, so as to better understand individual users’ needs and lighting preferences in study rooms. The research revealed the existence of various types of users with different personal preferences regarding lighting in order to feel comfortable and alert. A new conceptual lighting proposal is presented for the study room in KTH library, following an uneven lighting approach that utilizes different lighting zones to accommodate individual needs and affect the sense of comfort, alertness, and ultimately, the well-being of multiple types of users.


Introduction and background
The quality of lighting depends on the interaction between lighting, place, and person [1].Architecture can serve as a canvas to showcase the complexity of natural light [2].Light has the power to highlight architectural features, promote historical and aesthetic qualities, and elicit emotional responses.The satisfaction and preference of a space also involve an emotional component, influencing how it makes viewers feel [3].Some spaces are perceived as more inspiring than others, and light plays a significant role in creating such an atmosphere.Different lighting typologies and distributions can lead to varying perceptions and emotional responses within a space.For instance, uniform lighting can create a sense of detachment in space as well as less tension [4] compared to non-uniform lighting.Studies have shown that spaciousness can be enhanced with uniform lighting, while non-uniform and peripheral lighting can reinforce the experience of privacy [4,5].
Nowadays, it remains common to use artificial lighting to create even, uniform and sometimes characterless light effect in space.Standards promote this as well.This is probably a "relic" of the older types of lighting, like fluorescent lights, that had a typology and an illuminance output that supported bright and uniform lighting atmospheres.Although artificial lighting was invented to support visibility, during the last few years, more and more examples of "recommended illuminance levels being far in excess of levels required to satisfy visual performance needs" [6] are appearing.The norms and recommendations for illuminance levels, as well as common practice, may need to be reevaluated since in many cases they "exceed what is necessary for effective visibility" [7].Moreover, research has shown that rooms with non-uniform luminance distribution require less light to achieve equivalent brightness than those with uniform distribution, suggesting potential energy savings through lighting design [8].
Uniform lighting, although providing consistent illumination and accurate color representation, can feel static and unnatural, lacking variation and scale of importance [9].Pallasmaa points out that homogenous bright light can diminish the imagination and weaken the sense of place, affecting mental well-being and feeling of privacy [10].In contrast, non-uniform and varied lighting is common in natural environments, where sunlight produces dynamic patterns of illumination, color, and intensity.Humans are naturally connected to nature and have a collective memory of the effects of natural light.The preference for seeing without being seen and spatial arrangements that support movement and exploration can be attributed to this connection [4,11,12].
Throughout history, electric lighting has been associated with happiness, knowledge, cleanliness, and health.Light symbolizes truth, wisdom, and progress, while darkness is often linked to ignorance, oppression, and lack of control.Moreover, the transition between light and dark is associated with imagination, intimacy, and the supernatural [13].All these symbolic meanings, combined with the physiological effects of lighting, make the interplay between light and dark a fascinating subject.
Contrast and dark zones play an important role in highlighting the unique characteristics of architectural spaces, supporting visibility, and aiding orientation.Contrast is fundamental to vision and visual quality [14], while shadows and darkness create ambiguity, inviting peripheral vision and tactile fantasy [10].Focusing on light at vertical surfaces, brightness contrasts, and departure from uniformity can enhance spatial experiences and orientation [15].
However, contemporary office spaces and educational environments often employ mostly uniform lighting, which might be counterproductive to individual well-being, productivity, and costeffectiveness.Exploring alternative lighting designs that move away from uniformity could be helpful for fulfilling the vision of creating sustainable and comfortable lighting environments that cater to various needs.By understanding the interplay between light and dark and embracing the natural variations found in nature, architectural spaces can be enhanced, promoting beauty, comfort, and inspiration.
This investigation aims to shed light on the benefits of varied lighting options that can support individual well-being, productivity, and energy savings in contemporary educational spaces like libraries.The author's close connection with educational and library environments, as a recent student, influenced the choice to focus on library environments and study rooms.The hypothesis is that uniform lighting is inadequate to create sustainable and comfortable lighting environments that accommodate diverse needs.To explore this hypothesis, a uniformly lit study room in the KTH library in Stockholm will be thoroughly analyzed and evaluated.A new conceptual lighting proposal will be presented to correspond with the lighting preferences, visual comfort, and circadian rhythms of the space's diverse user types.

Research question
Main question: Is uniform or uneven lighting better for study rooms in libraries, in terms of well-being, concentration, alertness and comfort?Secondary questions: What is adequate light?Why do we overlight interior spaces?Why do we avoid shadows, dark zones?What do users need to feel comfortable and alert?1.2.Sustainable statement In order to promote sustainable practices, it is essential to prioritize the well-being of users and be aware that there is not one specific, correct way to study.In order to design quality study environments, the consideration of the multiple needs and preferences of users is crucial.Using as much natural light as possible and lighting control systems that follow the circadian rhythm and provide artificial lighting when and where is needed, can lead to sustainable designs that better support physical and mental health (correlation with UN Sustainable Development Goals 3 and 4 [16]).Implementing varied, energyefficient illumination with motion sensors in study rooms, using eco-friendly, recyclable materials for fixtures and setting illuminance thresholds responsibly after correct evaluation of standards (correlating with UN SDG 7) can lead to a more sustainable future.

Method and procedure
The study focused on a study space in the ground floor of the northern gallery in KTH library (Figure 1) to explore the possible negative aspects of uniform lighting.The space appeared uninteresting and had fewer visitors than other parts of the library.In order to better evaluate the chosen case study area, three additional study areas in Swedish libraries were visited and evaluated: the annex in Kungliga biblioteket, the southern wing of Stockholms Stadsbibliotek and the study hall at Ekonomikum, in Uppsala University.Personal observations and questionnaires to users were used to gather information concerning user preferences and the relationship between light distribution and comfort, alertness, and concentration.The research aimed to provide data for a new lighting proposal for the main study area in KTH library, which was assumed to be less advantageous than other study spaces (Figure 2).Both qualitative and quantitative research in the four study areas were expected to validate this assumption.

Areas of analysis Main Case Study Area -KTH Library:
The KTH library was renovated in 2002 by Ahrbom & Partners and was originally a machine laboratory designed by Erik Lallerstedt in 1917.The main study area of analysis on the ground floor of the northern gallery in KTH library, formerly a water gutter, can now accommodate around 30 seated people and is adjacent to the library's emblematic main hall, which receives ample daylight through skylights.Secondary Case Study Areas (see Table 1): Kungliga biblioteket's annex, designed by Murman Arkitekter and completed in 1997, is a glass-covered space with study desks around a staircase that receives abundant daylight.The southern wing of Stockholms Stadsbibliotek's historical building is a double-height room with desks for up to 10 users each.High windows provide direct and diffused daylight.Finally, the Ekonomikum study hall in Uppsala University, created in 2019 by Sweco Architects, aims to provide a peaceful and dimmed space with carefully placed light sources to accommodate diverse user preferences and promote concentration.

Qualitative study and participants
Four different study rooms in four Swedish libraries were visited and evaluated, first by the author and then by available users of the spaces.The evaluation involved observations, Visual and Physical lighting theory [14], questionnaires, and small interviews.The author's subjective evaluation included notes on available fixtures, light distributions, adjustability of the fixtures, connection with daylight, and general behavior of the users.The main topics of the questions asked to the users were visual comfort, concentration, and general lighting preferences between bright/uniform and dimmed/uneven light scenarios.The participants in the questionnaires were users of space present at the moment, mostly students aged between 18 and 35 that voluntarily agreed to be engaged in a conversation and anonymously be part of the research.In Kungliga biblioteket, Stockholms stadsbibliotek and Uppsala Ekonomikum, 8 users of each study space answered a questionnaire and evaluated the lighting conditions of the space through V/P Lighting theory [14].5 males and 3 females in Kungliga biblioteket, 3 males and 5 females in Stockholms stadsbibliotek and 3 males and 5 females in Uppsala Ekonomikum.Additionally, 31 people, 16 males and 15 females answered a questionnaire and evaluated the lighting conditions of the study room on the ground floor of northern gallery in KTH library, which is the study space that will be further analyzed in order to develop an improved lighting scenario.The evaluation took place on four different sunny dates in May at around 2:00 PM each day.Finally, 4 users of KTH library study room, 2 males and 2 females, were extensively interviewed about their subjective impressions concerning the study area.

Quantitative study
The quantitative study was conducted solely in the main case study area of the KTH library.Illuminance was measured on a formed grid in the space, with an illuminance meter placed at desk height levels (0.72m) during daytime (1:00 PM) to assess the overall uniformity (Figure 8).Additionally, luminance was checked on the desks, floor, and ceiling using the FusionOptix app and a luminance meter during daytime (1:45 PM).Finally, CCT and flicker from existing fixtures were measured using a spectrometer.

Limitations
The three secondary case study areas in Kungliga biblioteket, Stockholms Stadsbibliotek, and Uppsala Ekonomikum were not analyzed in the same level of detail as the main case study area in the KTH library, resulting in an uneven comparison.Fewer users participated in the questionnaire and interviews and less formal analysis of the lighting conditions was conducted.

Results
Through observations, the four analyzed study rooms were categorized into four different types based on their connection with daylight (skylight type, embracing type, uniform and neutral type, introverted and concentric zoning type, see Table 1).The qualitative research conducted in these four types of spaces revealed that different lighting conditions, with varied connections to daylight, attract different types of users with different needs (Figures 3-4).Users appreciate the lighting conditions and light distribution individually in the study areas they choose to work in, and they can be classified into different types based on their preferences for a comfortable and inspiring environment that helps them concentrate and stay alert while studying (Table 2).Evaluation of the case study rooms by their users indicates that they are mostly content with the lighting conditions.Natural daylight is highly appreciated by all.Among the users, those using the study room in the KTH library were the most dissatisfied with the lighting.They commented that the space feels oldish, uninspiring, dimmed, small and oppressive due to the low ceiling, and it lacks diversity or smaller private zones (Figure 7).Consequently, it is not their preferred choice compared to other rooms in the KTH library.However, it is frequently chosen as a seating area simply because it is rarely crowded.
The quantitative study in the KTH library's study room showed that the desks have lower horizontal illuminance than what is recommended by standards.
Finally, the conceptual design proposal presented for the study room in KTH library, which is the least pleasant and appreciated by its users among the four analyzed library areas, aims to incorporate multiple and adjustable lighting conditions in order to affect positively the users of space and create a varied and uneven light atmosphere that simultaneously accommodates the individual needs of multiple users in terms of concentration, alertness and comfort.Table 1.Observation of space and lighting conditions in the four case study areas.

Types of users and evaluation of case study areas
Table 2. Analysis of six identified users' types with different preferences in lighting conditions.

Literature Review
Three articles related to: a) the effect of light distribution on comfort, concentration, calmness, and energy efficiency [18], b) the comparison between adjustable and static lighting and their impact on human behavior and mood [19], and c) the contribution of light distribution and contrast to the perception of space [20], were analyzed as references for the conceptual design proposal (Table 3).
Table 3. Indication of the main findings through experiments, in the articles of the literature review.

Conceptual design proposal for the KTH library's study room
All the aforementioned results, along with some comments from the library administration, were used to develop a new conceptual lighting proposal for the KTH library's study room which aims to accommodate the needs of multiple users and introduces light zones with different light distributions and adjustable lighting (Figures 9-10, Tables 4-5).Table 5. Representation of the lighting conditions corresponding to users' needs, in each light zone included in the conceptual design proposal.
The design proposal tries to incorporate the needs of all user types identified and creates divided light zones that collectively form an inspiring, comfortable, and human-centered environment that is IOP Publishing doi:10.1088/1755-1315/1320/1/01200710 compatible with users' circadian rhythm and well-being, addresses their need for privacy or socialization [21], establishes a connection with daylight and the perception of time, and fosters a sense of orientation within the space.

Discussion
The research identified different types of users with varying lighting needs in the four case study areas.
The qualitative research showed that users' lighting preferences generally matched the provided lighting atmosphere in the study rooms, except for the KTH library's study room.For instance, users in the annex of Kungliga biblioteket, with abundant daylight, preferred bright environments for concentration, ranked privacy as the least important factor, and all of the participants in the questionnaire chose the bright and uniform lighting scenario.Conversely, users at Uppsala Ekonomikum, evaluated as an introverted space, preferred dimmed and warm environments with adjustable lighting and various light zones, considered privacy and comfort as top priorities, and all of them preferred the warm and varied lighting scenario in the questionnaire (Figure 5).While lighting conditions were not the primary factor influencing users' choice of study space, the extreme preferences in these two cases suggest a strong compatibility between user type and space type, indicating that users may select study areas that meet their needs or become accustomed to the provided lighting over time.However, educating users that are not familiar with the effects of illumination on their health and well-being, including the impact of correlated color temperature (CCT) on circadian rhythms, is essential.
The Uppsala Ekonomikum study room was evaluated most positively by its users, and that indicates an appreciation of the zoned lighting (Figure 6).Light zones are "(spatial) groupings of the lighting variables (intensity, direction, distribution and color)" [22] that, while interacting, can affect significantly the perception of space.Moreover, uneven and varied lighting leads to a variation in lighting conditions within the same space, which can consequently lead to an inspiring and versatile spatial environment with multiple lighting choices that can accommodate different needs.Interestingly, Uppsala Ekonomikum was at the same time the most disconnected study room from daylight, which was a factor much appreciated by participants in the questionnaires in all the four study rooms.Upssala Ekonomikum's example shows that careful lighting design that provides a pluralistic light atmosphere and adjustable lighting that can be controlled by users, reduces the discontent due to lack of daylight, at least to an extent.
It is supported by researchers and lighting professionals that contemporary public spaces, like study rooms in libraries, should be equipped with adjustable lighting, not only to allow individual use and control by users, but also to allow automated control (advanced dimming with daylight sensors and tunable white OLEDs) in order to be human-centric, follow the needs of users concerning circadian rhythm and emotional well-being, and be energy efficient and sustainable.According to Myriam Aries, "during the day, bright light (1000-2000lux) in a combination of daylight and electric lighting improves mood and motivation levels" [23].When there is not much daylight, artificial dynamic lighting could abstractly represent daylight and its visual effects, in order to reduce the results of its insufficiency and affect emotionally the users that could feel more connected to nature (e.g.projections of shadows of trees or water).
Concerning energy efficiency, controllable zoned lighting that is used when it's needed together with task lighting, uplighting, and wallwashing, can save energy comparing to the uniform downlighting of the study room in KTH library.The area was found to be adequate to standards in terms of lighting power density, however it was also found to have poor lighting that doesn't fulfill the wishes of users and could be improved.Standards (like EN 12464-1 [24]) are the only recognized tool for evaluating light quality.However, they still rely on a simplified understanding of how vision functions, which can lead to the installation of excessive lighting systems that can have negative impacts on both well-being and energy consumption [25].Careful reinterpretation of standards and zoned lighting with control systems and adjustability can be the means to create sustainable study room environments that satisfy their users.
Finally, as was mentioned in the introduction, although uniformity is not commonly found in nature, it was established together with an effort of overlighting, as a regular way of illuminating offices and public spaces like schools and libraries, at least during the last 60 years.Maybe we still broadly create uniform and overlit environments because it's an easy and quick method in terms of design and installation, or maybe because we are used to it.However, it is important to realize that less brightly and evenly lit environments could broaden the palette of perception and enhance the overall spatial experience.

Conclusion
From all the conducted research and since uniformity can accommodate the needs of only one category of users, uneven lighting seems more appropriate than uniform lighting for public study spaces that have the responsibility to satisfy multiple types of users and their individual needs concerning concentration, alertness and comfort.However, uniform lighting can be beneficial as a controlled scenario for certain situations like cleaning or workshops.Moreover, high-quality study environments should consider the diverse needs and preferences of users, avoiding a one-size-fits-all lighting approach.Prioritizing the well-being of all types of users in study rooms involves providing varied and uneven lighting atmospheres that facilitate both privacy and socializing, giving prominence to existing natural light, and implementing automated control lighting systems that align with the circadian rhythm and the daily passing of time.The conceptual proposal in this research took into account all of these insights and integrated them in the design in order to ameliorate problems with the existing study room in KTH library, with a primary objective of creating spaces that support physical and mental health through lighting, while corresponding to UN Sustainable Development Goals and the vision of a more sustainable future.Further research with added scopes should be conducted in the future concerning users' lighting preferences in study rooms and other public spaces, as well as real-scale testing to investigate the combination and cooperation of different light zones in space, as a whole.

Figure 1 .
Figure 1.The KTH library study room.Left: Ground floor plan of KTH Library (the analyzed area is marked), middle and right: existing situation, plan and lighting fixtures of the study room.

Figure 2 .
Figure 2. Factors that affected the formation of the design proposal.

Figure 3 .
Figure 3. Factors that affect the formation of a type of user in study rooms.

Figure 4 .
Figure 4. Connection of the four different study rooms with daylight and observation of how this affects the formation of different types of users with different needs concerning lighting.

Figure 5 .
Figure 5. Results derived from questionnaires answered by users of the study spaces in the four different case study libraries.Preference between uniform -bright -cold and varied -dimmed -warm lighting atmospheres in study environments.

Figure 6 .
Figure 6.Diagrams with users' opinion about the luminous atmospheric quality in Uppsala Ekonomikum's and in KTH library's study space.Green: positive comments, grey: negative comments.

Figure 7 .
Figure 7. Section and plan showing the perceived uniform light distribution.

Figure 9 .Table 4 .
Figure 9. Plan of the new conceptual proposal with different light zones that accommodate the needs of different types of users.Table 4. Proposed lighting scenarios for the study room in KTH library.

Figure 10 .
Figure 10.Section and perceived light distribution of the new conceptual proposal with different light zones that accommodate the needs of different types of users (daytime scenario).