Intensity and ratios of light affecting perception of space, co-presence and surrounding context, a lab experiment
Introduction
For many years, existing lighting codes and standards have relied mainly on illuminance levels on horizontal surfaces, likely because they are easier to measure. At the same time, research in lighting design has moved towards luminance-based metrics. Current standards include luminance, though illuminance is still the more commonly used measure in practice [1]. Fotios et al. state that the standards need to evolve and that parameters for the quantifying measures of pedestrian lighting should be based on vertical rather than horizontal illuminance measures, as vertical measures represent what the human eye perceives when observing the space [2]. Dubois et al. point out that illuminance measures the light falling on a surface from all directions while luminance measures light leaving a surface towards a specific location, implying that luminance better describes how the human eye perceive the brightness of a surface [1].
Lighting norms and standards often define minimum illuminance levels in relation to traffic and to people and the lighting requirements necessary for them to navigate and feel safe [2]. But there is an inherent contradiction between providing high-intensity of lighting and increasing perceived safety. High-intensity lighting enables you to perceive nearby details but might make surrounding areas appear dark and unpleasant. Therefore, in this study, we investigate how luminance intensity affects the perception of a space as well as how the ratio between the luminance intensity in the space and in the surrounding area affects perception of that space.
The study builds on a preliminary field study we conducted at two tram stations in Aarhus, Denmark to study the perceived qualities of light intensity in a complex context (see Fig. 1). The tram station study consisted of observations documented in a series of photos and short semi-structured interviews [3]. The study indicated that a high-intensity lighting can create a tense atmosphere and cause glare, making other travelers appear pale and the surrounding areas appear dark and difficult to perceive due to contrast. Analysis of traveler's perceptions suggested the potential of investigating how light intensity ratios and the hierarchy of light in surrounding areas affects user's perceptions the outdoor space they are situated in, their fellow travelers and the surrounding areas.
Lighting designers, architects and researchers have explored the perceived qualities of intensity and ratios of light. Using a phenomenological approach stresses the potentials of luminance intensity and ratios. In the book The eyes of the Skin, Pallasmaa [4] argues that most contemporary public spaces would be more enjoyable with lower light intensity and uneven light distribution. Pallasmaa describes the use of a constantly high level of illumination that leaves no space for mental withdrawal or privacy as an efficient method of mental torture. “Deep shadow and darkness are essential because they dim the sharpness of vision, make depth and distance ambiguous, and invite unconscious peripheral vision and tactile fantasy. Homogenous bright light paralyses the imagination in the same way that homogenization of space weakens the experience of being, and wipes away the sense of place.” The architect Zumthor illustrates another approach to the balance between light and darkness when he describes an idea about planning lighting by looking at a space as a “pure mass of shadow, where you put light in as if you were hollowing out the darkness, as if the light were a new mass seeping in” [5]. Pallasmaa explains, “the quality of an architectural reality seems to depend fundamentally on the nature of peripheral vision, which enfolds the subject in the space.” He continues, “the preconscious perceptual realm, which is experienced outside the sphere of focused vision, seems to be just as important existentially as the focused image. In fact, there is medical evidence that peripheral vision has a higher priority in our perceptual and mental system” [4]. The Lighting Designer Lam describes the architectural and social potential of light in the urban context: “Moving from the conception of ‘the more light the better’ to a more granular and refined understanding of light offers opportunities to create lighting solutions that respond to context, people and locality” [6]. As a tool for understanding the complexity of designing with the perceived qualities of different light levels, Cuttle defines three design characteristics in relation to brightness: (a) overall perceived brightness or dimness of illumination, (b) perceived difference of brightness of illumination between the design space and adjacent spaces, and (c) illumination hierarchy. The three design objectives highlight how brightness levels affect the appearance of a space, describing both the quality of light and visibility in the space and the quantity of light in the space [7]. Each of the scholars discussed above stresses the importance of the perception of differences in intensity and the need to understand relationship between relative intensities in terms of a spatial hierarchy with much greater complexity than even luminance level. The concept for this lab experiment is derived from research within the architectural tradition, as described in the introduction [[4], [5], [6]], and the following text describes the research within the lighting industry used to define the lab experiment and frame the test parameters.
Section snippets
Framing test parameters
Researchers have identified several strategies for investigating pedestrians' responses to outdoor lighting and their subjective assessments of lighting quality [[8], [9], [10], [11]]. In their research, Caminada and Van Bommel classify the objectives of requirements for outdoor lighting into four categories: detection of obstacles, visual orientation, identification of persons and pleasantness and comfort [12]. Previous research investigates whether lighting conditions for pedestrians in urban
Test setting
The light lab measures 5.8 m × 5.8 m, with a ceiling height of 4.2 m. One wall is painted matt white, and three walls are covered with black Molton curtains. The floor is covered with gray linoleum, and the ceiling is white with a rig for mounting fixtures.
We divided the lab into two light zones to simulate a waiting area and the surrounding context. We placed two chairs in the waiting area, one for the test participant and one for the interviewer. To simulate a shelter and provide lighting for
Results
We analyzed responses to the 12 questions separately, across all lighting scenarios. First, we looked for potential outliers in the responses but did not identify any (i.e., no participant was further away from the mean than three times the standard deviation). We separated the lighting scenarios based on the luminance levels in the surrounding area (i.e., LS1-LS3, which had 20 lux; LS4-LS6, which had 5 lux) as they resembled different times of day and/or different urban contexts. We then
Discussion
According to international and Danish lighting regulations [45], demands for illuminance intensity are defined in relation to the traffic flow and the pedestrian's ability to navigate and feel safe. Research has found that high illuminance uniformly distributed meets these criteria [8,15,27,29] and outdoor public space lighting designers and engineers tend to recommend high lighting intensities to support visibility and increase perceptions of safety. But in this lab experiment, we found test
Conclusion
There is an inherent contradiction between providing high-intensity lighting and increasing perceived safety. Bright lighting allows improved perception of nearby details but may make the surrounding context appear dark and unpleasant, leading to perception of decreased safety. High intensity in local lighting can also impair perception of the surrounding city and cast unpleasant light on people in the space.
To better understand how luminance intensity influences this situation, we designed
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This research is part of a Ph.D. project in urban architectural lighting and we would like to thank our industrial partners Schréder(BE) and Holscher Design (DK). Furthermore, we would like to thank the Lighting Design Research Group at Aalborg University Copenhagen, Denmark as well as the 30 test participants for their time.
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