Achieving visual balance for screen-based tasks in multifunctional bedrooms: roles of task illuminance, correlated color temperature, and color rendering

Abstract

Student dormitory bedrooms increasingly function as multifunctional spaces for rest and intensive screen-based work, yet typical bedroom lighting is set to standard or minimal levels rather than tailored to the visual demands of digital tasks. This mismatch can produce tonal and illuminance contrast that impair comfort and performance. An experimental study was conducted in a controlled dormitory setting. Eight lighting scenarios were evaluated by combining daylight with either direct or indirect task lighting at CCTs ranging from 3,000 to 6,500 K. Visual balance was assessed using three performance metrics: task to ambient illuminance ratio (Rlx), correlated color temperature difference (ΔCCT), and color rendering index difference (ΔCRI). Measurements were collected across three daytime periods. Direct lighting combined with daylight consistently achieved task-to-ambient illuminance ratios within or close to recommended range, whereas indirect wall-bounced lighting generally produced under-illuminate task planes. Task-light CCTs of 3,000–4,000 K reduced spectral contrast between the laptop screen and surrounding room surfaces, resulting in the smallest ΔCCT values. Lower CCTs, particularly 3,000 K, also produced higher color rendering quality and the smallest ΔCRI values between task and ambient zones. Lighting configuration had a limited effect on color rendering consistency compared with CCT. The findings indicate that visual balance in multifunctional student bedrooms cannot be achieved through ambient lighting alone. A warm-to-neutral task-lighting strategy (3,000–4,000 K) combined with direct task illumination provided the most balanced performance across illuminance, spectral contrast, and color rendering metrics. These results offer practical guidance for designing residential study environments that better support visual comfort and screen based work.

1 Introduction

Traditionally, bedrooms—particularly in student dormitories—have been perceived as spaces primarily intended for rest and sleep. However, the widespread adoption of digital technology has altered this perception, transforming bedrooms into multifunctional spaces that also function as study areas, workstations, and settings for extended laptop use (Alom et al., 2023; Dişli and Arslan, 2023; Li et al., 2022). This shift was accelerated during the COVID-19 pandemic, when remote learning and work practices necessitated prolonged use of personal devices within confined residential spaces.

Although bedrooms are still commonly designed with a primary emphasis on relaxation, often incorporating calming features such as neutral wall colors (e.g., white, light beige, and soft gray tones) and wooden furnishings, such designs are insufficient to meet the evolving functional demands (Al-Qamadi, 2024). Many conventional bedroom lighting schemes rely on a central ambient light source—such as ceiling-mounted recessed downlights—which provide broad, diffused illumination intended primarily for general visibility and relaxation (Al-Qamadi, 2024; JEM Energy Inc. and CEATI International, 2010; Shishegar and Mohamed, 2022). However, such setups are inadequate for supporting screen-based tasks, which require more localized and precise illumination to enhance visual acuity and reduce strain during activities such as reading fine text or performing detail-oriented tasks on laptops (Shishegar and Mohamed, 2022; Canazei et al., 2019).

This disparity between traditional bedroom designs, which focus on relaxation, and the growing need for higher visual acuity for screen-based tasks necessitates a reevaluation of lighting strategies in these spaces. The challenge lies in accommodating both restorative and productive functions without compromising the wellbeing or performance of the occupant. This gap in current lighting design underscores the need for innovative solutions that integrate task lighting with ambient illumination to better support extended screen use in multifunctional bedroom environments.

2 Fundamentals

This section introduces the theoretical foundation for optimizing lighting in multifunctional student bedrooms, where visual balance—the relationship between screen luminance and surrounding surfaces—is critical for reducing eye strain during digital tasks. To maintain safety and comfort, general screen-based tasks require horizontal illuminance of 300–500 lx and a task-to-ambient illuminance ratio () between 1.00 and 1.67 control local contrast. Beyond intensity, neutral CCT settings of approximately 4,000 K and a CRI ≥80 are recommended to promote alertness and color fidelity, particularly in warm-toned dormitory environments where artificial light must act as a “spectral bridge” between cool screens and ivory surfaces to achieve spectral unity. The efficacy of these standards is further influenced by the ergonomic configuration of task lighting, contrasting direct lateral illumination—which provides targeted intensity—with indirect, wall-reflected approaches designed to diffuse light and mitigate veiling reflections. Finally, these fundamentals are synthesized into a research framework that evaluates how visual balance, spectral unity, and color-rendering consistency collectively contribute to balanced visual conditions throughout the day. In this study, visual balance is defined as the overarching condition describing the perceptual equilibrium among the self-luminous laptop screen, the task area, and the surrounding ambient environment during extended screen-based work. Within this framework, spectral unity refers to the tonal coherence between light sources and reflected room surfaces, while color-rendering consistency describes the uniformity of color fidelity across both task and ambient zones.

2.1 Visual balance and lighting requirements for screen-based tasks

Screen-based tasks, such as studying and working on laptops, require a carefully designed lighting environment to ensure visual comfort and minimize visual strain (Han et al., 2021; European Committee for Standardization, 2002). Visual balance—defined as the appropriate relationship between the luminance of a self-luminous screen and the luminance of surrounding room surfaces—plays a central role in reducing eye fatigue during prolonged laptop use (Han et al., 2021; Xu et al., 2025). Achieving visual balance ensures that screen brightness is appropriately complemented by ambient lighting, thereby preventing excessive luminance contrasts that may cause discomfort or impair focus (Yan et al., 2025; Shamsul et al., 2013; ISO 9241-3, 1992).

The Illuminating Engineering Society recommends horizontal illuminance levels of 300–500 lx for general screen-based tasks, with up to 1,000 lx for detailed visual work (ANSI/IES RP-1-22, 2022). Both the absolute illuminance level and its spatial distribution across the task area and adjacent surroundings significantly influence the speed, safety, and comfort with which individuals perceive and perform visual tasks (European Committee for Standardization, 2002). Illuminance levels in the surrounding areas should align with those of the task area to maintain balanced luminance distribution within the field of view, as large spatial variations can induce visual stress and discomfort. Although the illuminance of surrounding areas may be lower than that of the task surface, it must not fall below the minimum values specified in Table 1 of relevant lighting standards.

To operationalize the requirements outlined in Table 1, the present study expresses the standard in terms of an illuminance ratio between the task area and its immediate surroundings, determined through Equation 1.Where is the task illuminance on the horizontal workplane and is the illuminance of the immediate surrounding areas within the near-field view. Table 1 specifies the lower bound . Based on these tabulated limits, the implied ratios are as follows: when (as must be not less than ); for ; and for . As the experimental conditions in this study target typical desk-task illuminance levels ranging from 150–500 lx, the operative task-to-surround constraint derived from Table 1 is summarized as Equation 2.

This ratio range was adopted to control local illuminance contrast in the near-field visual environment and to maintain balanced luminance transitions between the task surface and its immediate ambient surroundings during prolonged work periods. In this study, the ratio is applied specifically to near-field workstation conditions in screen-based dormitory environments, where students engage in extended digital tasks on laptops, thereby operationalizing localized task-to-ambient visual balance within the immediate field of view.

Beyond illuminance, light quality metrics such as correlated color temperature (CCT) and color rendering index (CRI) play a pivotal role in ensuring visual comfort (WELL v02 L08, 2020), with the established standards for these variables summarized in Table 2. The WELL v02 L07, 2020, feature requires either a CRI ≥90 or a CRI ≥80 with R9 > 50 to ensure accurate color perception and reduce eye strain. Similarly, European Committee for Standardization (2002) specifies that a CRI (Ra) ≥80 is essential for tasks requiring high visual acuity, including those involving digital screens. A neutral-white CCT of approximately 4,000 K is commonly recommended to balance visual comfort and alertness during prolonged screen exposure (U.S. Department of Energy, 2024; Van de Perre et al., 2023). By contrast, lower CCT values (e.g., 3,000 K) promote relaxation but may reduce cognitive stimulation, whereas higher values (5,000–6,500 K) enhance alertness yet increase the risk of visual discomfort if not supported by appropriate surrounding ambient lighting balance (Zhou and Pan 2023; Golmohammadi et al., 2021; WELL v02 L08, 2020 reinforces these principles by emphasizing high-quality electric light design optimized for visual performance in work environments.

In luminous environments such as student dormitories with predominantly warm-toned interior surfaces (e.g., ivory walls and floors), the spectral power distribution of the combined lighting system—including daylight, ambient recessed lighting, tunable task lighting, and self-luminous screens—is significantly influenced by room surface reflectance, which dominates indirect illuminance and influences the overall CRI through multiple reflections (Cai et al., 2018). Experimental evidence further demonstrates that the preference for warm (3,000 K) or cool (6,500 K) white light depends on interior surface colors, with optimal visual comfort and perceptual uniformity achieved when the CCT of the lighting aligns with surface warmth. For example, warm light has been shown to enhance positive mood in neutral or white environments, whereas cooler light is better suited to spaces with cooler tones. This effect is attributed to minimized spectral mismatch in reflected spectra (Shahidi et al., 2021). Consequently, greater spectral unity within the luminous environment—often achieved through intermediate CCT settings (e.g., 4,000 K)—elevates CRI by reducing contrast between disparate light sources, thereby bridging ambient lighting conditions with supplemental task provisions.

Beyond illuminance and color temperature, visual balance is also governed by the relationship between task lighting and ambient lighting (Yan et al., 2025; ISO 9241-3, 1992; Fan et al., 2024; Rossi et al., 2023). Effective task lighting, in combination with ambient lighting that prevents reflections and glare, is essential for reducing visual fatigue (Fan et al., 2024; Lin et al., 2008; ISO 9241-6, 1999; ANSI/IESNA RP-1-04, 2004). Reflected glare and veiling reflections from display screens—caused by light reflected from the surface of the screen or nearby objects—can significantly decrease screen visibility and increase visual discomfort during prolonged laptop use (ANSI/IES RP-1-22, 2022; ANSI/IESNA RP-1-04, 2004; ISO 9241-6, 1999). As a result, a key challenge in designing lighting for screen-based tasks is finding the right balance in which the task area is brightly illuminated for optimal performance while surrounding room surfaces are controlled to prevent excessive contrast or glare.

In this context, maintaining consistency in color rendering between the task area and the surrounding ambient lighting is essential for visual harmony. When the lighting spectrum and tone of the task and surrounding zones are aligned, visual contrast is reduced, enhancing the perceived coherence of the space and contributing to a balanced and comfortable visual environment. Studies have shown that consistent color rendering across different zones helps minimize discrepancies in lighting conditions, thereby fostering a more cohesive and pleasant visual experience (Abeysekera et al., 2020). Improved color rendering consistency enhances visual balance, which contributes to reduced visual fatigue and supports better task performance. Moreover, when lighting across different zones is more uniform, the lighting conditions feel less stark or distracting, leading to a more harmonious and comfortable environment for occupants (Neumann and Schanda, 2006). Therefore, achieving consistent color rendering throughout the space is crucial for establishing a comfortable and visually balanced lighting setup.

The European Committee for Standardization (2002) standard further emphasizes the importance of lighting configurations that minimize excessive contrast between the display screen and the surrounding surfaces. Sharp contrasts between task and ambient lighting should be avoided, as these can lead to eye strain. Both the CCT of the light sources and their spatial distribution play a significant role in maintaining a balanced environment that supports visual performance while minimizing fatigue. Therefore, effective lighting for screen-based tasks must achieve a balance between ambient lighting (general room illumination) and task lighting (direct or indirect lighting for the desk) to avoid areas of high contrast that could contribute to visual discomfort.

2.2 Task lighting for screen-based tasks

In contrast to traditional ambient lighting, task lighting plays a critical role in screen-based environments by supporting visual comfort and optimal performance. Conventional task lighting setups in bedrooms often rely on central ambient light sources that provide uniform, diffuse illumination (Wang et al., 2025; Gou et al., 2023). However, these sources are insufficient for tasks that require focused, high-intensity illumination, including reading or typing on a laptop. Task lighting addresses this limitation by providing the required intensity—typically in the range of 300–500 lx—in localized areas such as the desk to support detailed visual tasks without glare.

The most commonly recommended ergonomic configuration for task lighting is direct lighting, wherein lamps are positioned to deliver the light directly onto the work surface (workplane) (Canadian Centre for Occupational Health and Safety, 2025; Newsham, 2005). This configuration provides focused illumination precisely where visual tasks are performed, enabling users to supplement ambient lighting with targeted light tailored to specific activities such as screen viewing or paper-based work. By positioning adjustable luminaires laterally to the workplane, direct task lighting minimizes shadows and veiling reflections while maintaining user control over light direction.

An alternative ergonomic approach is indirect task lighting, wherein the lamp is aimed toward the wall behind the laptop to create a wall-reflected lighting effect (Yan et al., 2025; Joines et al., 2015). This approach helps diffuse the light more evenly across the workspace, helping to reduce glare and veiling reflections on the screen. Indirect lighting has been shown to enhance user satisfaction and reduce visual fatigue by maintaining a more uniform lighting environment around the task area. This approach is particularly effective in mitigating visual discomfort caused by excessive contrast between the screen and its surrounding surfaces.

Both direct and indirect task lighting configurations offer distinct advantages, and their effectiveness largely depends on the nature of the task and the overall lighting environment. Previous studies (Veitch et al., 2025; Boyce et al., 2006; Vries et al., 2021) have shown that a hybrid configuration, combining both direct and indirect lighting, can provide the optimal balance, reducing glare while ensuring adequate task illumination.

2.3 Overview of the study

This study investigates the effect of varying lighting conditions on visual balance in environments characterized by prolonged digital screen use, such as student dormitories. The primary objective of this study is to address the existing knowledge gap regarding how lighting parameters influence visual balance and task performance in multifunctional residential spaces. Understanding these relationships is crucial for developing effective and sustainable lighting solutions for screen-based tasks in modern living environments. By focusing on practical and affordable lighting solutions, this research aims to identify lighting optimizations that support both restorative and productive functions within shared spaces.

3 Material and methodology

3.1 Experiment setting

The experiment was conducted in a student dormitory bedroom measuring 4 m × 3.8 m (Figure 1), featuring a north-facing bouven-type light window, with the working desk positioned beneath it. The room included warm ivory wall and floor finishes, a white ceiling, and dark brown furniture, thereby creating a controlled luminous environment. The lighting system consisted of daylight entering through the window, a centrally located recessed downlight at the room’s center, and an adjustable study lamp with a tunable CCT (CCT range: 3,000–6,500 K) positioned to the right side of the desk.

FIGURE 1

The working desk served as the primary focal area of the experiment. A laptop was operated in normal mode and displayed a white screen at maximum brightness to simulate a standardized worst-case indoor scenario mimicking high outdoor luminance conditions. This configuration was selected to provide a consistent baseline for evaluating the effects of task lighting. A white screen offers a uniform spectral distribution compared with dynamic or content-rich displays, ensuring that any observed lighting effects are solely attributed to ambient illumination and task lighting. The use of maximum brightness was selected to maintain objectivity, as it represents an extreme but consistent condition, thereby enabling a clear assessment of interaction between the lighting dynamics on the working desk and the surrounding ambient environment.

The measurement campaign was conducted in Depok, West Java, Indonesia, between December 5–7, 2025. During this period, the percentage of cloud cover varied throughout the day. The cloudiest period occurred around 1:30 a.m., with a 94% probability of overcast or mostly cloudy conditions, whereas the clearest period occurred around 10:30 a.m., when the probability of clear or partly cloudy skies decreased to approximately 20%. These observations indicate that the experimental observations were obtained under a predominantly overcast seasonal context, even though brief clearer intervals were statistically possible around late morning hours.

3.2 Lighting scenarios

Eight lighting scenarios were systematically designed to isolate the contributions of daylight (DL) and task lighting (TL) variations, including CCT settings of 3,000, 4,000, 5,000, and 6,500 K, as detailed in Table 3. These scenarios included a control condition with DL only and two targeted intervention categories. The first category comprised direct TL configurations (DL + TL1 3,000, DL + TL1 4,000, DL + TL1 5,000, and DL + TL1 6,500) for focused workplane illuminance. The second category consisted of indirect, wall-bounced TL combinations (DL + TL2 3,000, DL + TL2 4,000, DL + TL2 5,000, and DL + TL2 6,500), designed to provide diffused illumination to the surrounding environment. This factorial approach enabled a comparative evaluation of luminous quality parameters under controlled lighting manipulations, bridging ambient dependencies with supplemental task provisions in the dormitory setting.

TABLE 3

​	Lighting scenario
	Daylight (DL): Only natural light from the bouven-type light window
	a. Daylight and Task Light 1 3,000K (DL + TL1 3,000K): Combination of natural daylight and direct task lighting with a 3,000K CCT. b. Daylight and Task Light 1 4,000K (DL + TL1 4,000K): Combination of natural daylight and direct task lighting with a 4,000K CCT. c. Daylight and Task Light 1 5,000K (DL + TL1 5,000K): Combination of natural daylight and direct task lighting with a 5,000K CCT. d. Daylight and Task Light 1 6,500K (DL + TL1 6,500K): Combination of natural daylight and direct task lighting with a 6,500K CCT.
	a. Daylight and Task Light 2 3,000K (DL + TL2 3,000K): Combination of natural daylight and indirect wall-bounced task lighting with a 3,000K CCT. b. Daylight and Task Light 2 4,000K (DL + TL2 4,000K): Combination of natural daylight and indirect wall-bounced task lighting with a 4,000K CCT. c. Daylight and Task Light 2 5,000K (DL + TL2 5,000K): Combination of natural daylight and indirect wall-bounced task lighting with a 5000K CCT. d. Daylight and Task Light 2 6,500K (DL + TL2 6,500K): Combination of natural daylight and indirect wall-bounced task lighting with a 6,500K CCT.

Lighting scenario.

3.3 Dataset collection

Illuminance (lx), CCT, and CRI were measured using an Opple Light Master 4 spectrophotometer at predefined locations and under all lighting scenarios. The measurement layout and technical setup are illustrated in Figure 2. Room-wide ambient conditions () were first established by averaging measurements obtained from eight locations (E1–E8) spaced 1 m apart at a desk height of 0.8 m, capturing the baseline control environment. was subsequently determined from two points located proximal to the workstation to support contrast analysis relevant to visual tasks around the workstation. Task-specific measurements were conducted at the workstation directly in front of the laptop, with the screen conditioned as described in Section 2.1. The sensor was positioned 0.6 m away from the screen, aligned parallel to the display plane and oriented vertically to represent the ergonomic perspective of a seated user engaged in screen-based activities. Horizontal workplane () readings were measured at this location to ensure compliance with standard illuminance measurement protocols for receiving surfaces and to enable direct comparability with values. Vertical workplane () measurements were performed to account for the self-luminous vertical light emission from the laptop screen and the primary vertical light exposure experienced by the user facing the display. Measurements were collected across three time windows—morning (07:00–08:00), noon (11:00–13:00), and afternoon (15:00–17:00)—to capture the influence of diurnal variations in daylight conditions.

FIGURE 2

3.4 Data analysis

The data analysis framework was structured to evaluate visual balance using objective lighting performance metrics. Analyses were conducted separately for illuminance, CCT, and CRI, followed by an integrated interpretation of results across different times of day.

3.4.1 Analysis for research question 1 (Q1): task–ambient illuminance balance

To address Q1, horizontal illuminance measurements were analyzed for both the and . A task-to-ambient illuminance ratio was calculated for each lighting scenario and time of day through Equation 1.

Ratio values within the range of 1.0–1.67 indicate balanced visual conditions, values below 1.0 indicate under-lit task areas, and values exceeding 1.67 indicated excessive contrast.

Lighting scenarios were classified based on their compliance with this range, and differences between direct (TL1) and indirect (TL2) task lighting ergonomic configurations were examined through descriptive and comparative analyses. This approach directly tests Hypothesis H1a by assessing the extent to which different lighting ergonomic configurations minimize high-contrast illuminance conditions.

3.4.2 Analysis for research question 2 (Q2): spectral contrast (CCT)

To evaluate spectral uniformity in response to Q2, CCT was analyzed for both the light emitted from the laptop screen and the surrounding near–working-desk ambient environment, focusing on how task-light CCT modifies this relationship during extended laptop use. Spectral contrast was quantified using the absolute difference between the vertical CCT measured at the screen plane and the ambient CCT, as determined through Equation 3.

Lower ΔCCT values indicate reduced spectral contrast and improved tonal coherence between the working desk area () and its , reflecting enhanced visual balance. Differences in ΔCCT were analyzed across task lighting CCT settings (3,000–6,500 K) and between direct and indirect ergonomic configurations to assess how warmer-to-neutral tunings (3,000–4,000 K) mediate the spectral disparity between the cool laptop screen and the warm-to-neutral room.

Analyses of variance (ANOVA) were conducted to determine whether warmer-to-neutral task lighting significantly reduced spectral contrast, thereby testing Hypothesis H2a. In addition, at the screen plane was examined to assess the stability of spectral distribution under different lighting scenarios, including variations in the CCT and ergonomic configuration of task lighting (direct vs. indirect).

For the CCT model, the Shapiro–Wilk test indicated no significant departure from normality, W = 0.98, p = 0.249. Therefore, the normality assumption for ANOVA was considered satisfied.

3.4.3 Analysis for research question 3 (Q3): consistency of color rendering

To address Q3, color rendering quality was assessed by measuring CRI values across all lighting scenarios. The mean CRI values were first analyzed to ensure compliance with the recommended minimum threshold of Ra ≥80, as outlined in lighting standards for tasks requiring high visual acuity, including screen-based activities.

ANOVA was then applied to CRI measurements across sampling points to assess the spatial consistency of color rendering within the working desk area and the surrounding ambient environment. This analysis facilitated evaluation of spectral consistency across different light sources and their interaction with warm-toned dormitory surfaces and cool laptop screens, as described in Hypothesis H3a. Specifically, the analysis tested whether intermediate CCT tunings (3,000–4,000 K) yielded higher CRI values, leading to improved color rendering quality compared with cooler settings (5,000–6,500 K), especially in warm-toned environments.

For the CRI model, the Shapiro–Wilk test indicated no significant departure from normality, W = 0.94, p = 0.222. Therefore, the data met the normality assumption required for ANOVA.

Further, comparisons between direct and indirect task lighting configurations were conducted to determine whether wall-bounced lighting (indirect) provided more consistent color rendering across the task area relative to direct task lighting. This component of the analysis directly addressed Hypothesis H3b by examining whether the lighting configuration (direct vs. indirect) significantly influenced the spectral consistency of color rendering, thereby affecting visual comfort and color fidelity during screen-based tasks.

3.4.4 Analysis for research question 4 (Q4): integrated evaluation of lighting scenarios

For each lighting scenario, mean values for all metrics were calculated across all measurement periods (morning, midday, and afternoon). Task-to-ambient illuminance ratio compliance was assessed relative to the recommended range of 1.00–1.67. ΔCCT values were used to quantify spectral contrast between task and ambient lighting, while CRI values were interpreted to assess the degree of color rendering consistency between the task area and its surrounding environment. In this context, smaller ΔCRI values indicate more uniform rendering across the near-field visual scene. Lighting scenarios were compared using a multi-criteria decision matrix approach, allowing simultaneous evaluation across illuminance balance, spectral uniformity, and color rendering consistency. The results were summarized using a heatmap-based visualization, which facilitated rapid comparison of lighting scenario performance across metrics and supported the identification of configurations that maintained balanced visual conditions throughout the day.

4 Results

4.1 Task–ambient illuminance ratio across lighting scenarios

The task–ambient illuminance ratio varied systematically across lighting scenarios (Figure 3), indicating that lighting configuration substantially influenced visual balance at the working desk. Scenarios combining daylight with direct task lighting (DL + TL1) consistently produced ratios within, or close to, the recommended range for visual balance (1.00 ≤ R ≤ 1.67). In particular, DL + TL1 with CCTs of 3,000–5,000 K yielded mean ratios between 1.44 and 1.45, suggesting a well-balanced relationship between task illuminance and .

FIGURE 3

By contrast, indirect wall-bounced task lighting scenarios (DL + TL2) generally yielded lower ratios, with mean values below 1.00 (0.82–0.89) at similar CCTs. These results indicate under-illuminated task conditions relative to the ambient environment, despite some mitigation of luminance contrast. Therefore, DL + TL1 demonstrated superior efficacy in normalizing excessive baseline ratios (>1.67) and bringing them into a balanced range.

Overall, DL + TL1 consistently achieved task–ambient ratios within the recommended visual balance range, whereas DL + TL2 resulted in ratios below unity, indicating insufficient task dominance.

4.2 Effects of tunable CCT and lighting configuration on spectral balance

4.2.1 Mean ΔCCT by lighting scenario

Spectral contrast between the task area and the surrounding ambient environment (Figure 4), quantified as the absolute difference in CCT (ΔCCT), differed substantially across lighting scenarios. The daylight-only condition (DL) produced the highest spectral mismatch between the working desk and its near-surrounding area (mean ΔCCT: 440.5 K), indicating that the baseline environment already contains substantial tonal non-uniformity in the immediate task field.

FIGURE 4

Among the task-lighting scenarios, TL1 at 3,000–4,000 K produced the lowest ΔCCT values (∼202–260 K), whereas higher CCT settings (5,000–6,500 K) increased spectral contrast. Indirect wall-bounced task lighting (TL2) generally yielded higher ΔCCT values, particularly at higher CCT settings, with the largest mismatch observed for TL2 at 6,500 K (347 K). These results indicate that warmer task lighting reduces spectral contrast.

4.2.2 Two-way ANOVA of CCT by tunable lighting and configuration

A two-way ANOVA performed on vertical-illuminance CCT measured at the working desk () showed a significant main effect of tunable lighting (Table 4) [F (3, 64) = 37.83, p < 0.001, η²_p = 0.64]. The lighting configuration also exhibited a significant effect [F (1, 64) = 5.55, p = 0.022, η²_p = 0.08], indicating systematic differences between direct and indirect task lighting. Importantly, a significant interaction between tunable lighting and lighting configuration was observed [F (3, 64) = 3.65, p = 0.017, η²_p = 0.15], suggesting that the effect of CCT on spectral characteristics at the working desk was dependent on whether the task lighting was applied in a direct or indirect configuration.

Post hoc comparisons showed that lower CCT settings (3,000–4,000 K) differed significantly from higher settings (5,000–6,500 K) (Table 5), with progressively larger mean differences observed as CCT increased (all p < 0.01). Interaction-level post hoc analyses further indicated that, at higher CCTs, TL1 produced significantly higher working-desk CCT values than TL2, particularly at 6,500 K (p = 0.019). Estimated marginal means confirmed that TL2 configurations consistently yielded lower vertical CCT values than TL1 at equivalent tuning levels (Figure 5). Collectively, these findings support Hypothesis H2b, demonstrating that warmer CCT settings combined with indirect, wall-bounced task lighting promote more uniform spectral conditions at the working desk.

FIGURE 5

4.3 Effect of color rendering and lighting configuration

4.3.1 Mean ΔCRI by lighting scenario

Color rendering contrast between the working desk area and the surrounding ambient environment, quantified as the absolute difference in the CRI (ΔCRI), varied substantially across lighting scenarios. The daylight-only condition exhibited a high mean ΔCRI value of 10.82, indicating a color mismatch between the working desk and its surroundings (Figure 6). Similarly, the combination of daylight with direct task lighting with the coolest CCT (DL + TL1 6,500) exhibited the highest mean ΔCRI value of 11.49, indicating a substantial color mismatch between the working desk and its surroundings.

FIGURE 6

TL1 at 3,000 K (DL + TL1 3,000) produced the lowest ΔCRI value (1.88), indicating the highest degree of color balance between the task area and the surrounding room ambiance. As CCT increased to higher values (5,000–6,500 K), color contrast also increased. TL2 generally resulted in higher ΔCRI values, particularly at higher CCT settings, with the largest color mismatch observed for TL2 at 6,500 K (8.12).

4.3.2 Two-way ANOVA of CRI values by tunable lighting and configuration

CRI analysis revealed a significant main effect of tunable lighting CCT on the CRI at the working desk [F (3, 64) = 13.76, p < 0.001, η²_p = 0.39] (Table 6). Lower CCT settings were associated with higher CRI values, with the mean CRI exceeding 90 at 3,000 K and gradually decreasing to 6,500 K. By contrast, the lighting configuration (direct vs. indirect) did not exhibit a significant main effect on the CRI [F (1, 64) = 0.04, p = 0.834, η²_p = 0.001], and the interaction between CCT and configuration was also not significant [F (3, 64) = 0.70, p = 0.558, η²_p = 0.03].

Post hoc comparisons confirmed that CRI values at 3,000 K were significantly higher than those at 5,000 K (p ≤ 0.003) and 6,500 K (p ≤ 0.001) (Table 7), regardless of lighting configuration. Additionally, CRI values at 4,000 K were significantly higher than those at 6,500 K (p ≤ 0.001). Estimated marginal means showed that both TL1 and TL2 maintained CRI values above 80 across all conditions, thereby satisfying the minimum recommended standards for screen-based tasks (Figure 7). Although indirect lighting did not significantly increase CRI values relative to direct lighting, it maintained comparable color fidelity while offering more spatially distributed illumination.

FIGURE 7

4.4 Integrated performance of lighting scenarios across visual balance metrics

To address Q4, an integrative evaluation was conducted to identify lighting scenarios that consistently minimized contrast between the working desk and the surrounding ambient lighting across different times of day, in accordance with EN 12464-1 recommendations. Performance was assessed using three objective metrics: task–ambient illuminance ratio compliance, mean spectral contrast (ΔCCT), and mean color rendering performance (ΔCRI).

Across all evaluated scenarios, configurations combining daylight with TL1 demonstrated the most stable performance throughout the day (Figure 8). In particular, DL + TL1 at 3,000–5,000 K showed the highest consistency in maintaining task–ambient illuminance ratios within or close to, the recommended range (1.00–1.67) while avoiding both under-illuminated conditions (<1.00) and excessive contrast (>1.67).

FIGURE 8

In terms of spectral balance, DL + TL1 scenarios exhibited lower and more moderate mean ΔCCT values than indirect task lighting configurations, indicating reduced spectral contrast between the task area and the surrounding environment. This effect was especially pronounced at 3,000 and 4,000 K, where ΔCCT values remained comparatively warm and neutral.

Color rendering balance between the working desk area and the surrounding room was further supported by the use of task lighting configurations. Across all tunable lighting conditions, in both direct and indirect scenarios, ΔCRI values remained low—especially at 3,000 and 4,000 K—indicating more balanced color distribution at the working desk.

An integrated comparison of all evaluated metrics revealed that the DL + TL1 configuration at 3,000–4,000 K most consistently achieved balanced illuminance, spectral contrast, and stable color rendering throughout the day. By contrast, indirect task lighting scenarios (TL2)—particularly at higher CCT levels (5,000–6,500 K)—more frequently resulted in elevated task–ambient contrast or increased spectral and color mismatch.

Overall, these results identify ergonomic lighting configurations that combine direct task lighting with warmer-to-neutral CCTs as the most effective solution for maintaining visual balance under dynamic daylight conditions, thereby addressing Q4 and supporting Hypothesis H4.

5 Discussion

5.1 Task–ambient illuminance ratio across lighting scenarios

The analysis of the task–ambient illuminance ratio revealed that only scenarios combining daylight with direct task lighting (DL + TL1) consistently achieved values within—or close to—the EN 12464-1 (European Committee for Standardization, 2002)–derived target range of 1.0–1.67. By contrast, indirect wall-bounced configurations (DL + TL2) generally produced ratios below 1.0, indicating under-illuminated task planes relative to adjacent ambient surfaces. These findings directly address RQ1 and partially support Hypothesis H1a by demonstrating that compliance with the recommended ratio in the tested dormitory bedroom is highly sensitive to the directionality of task lighting and the geometry of the measurement, with measured on the horizontal workplane and sampled at adjacent near-field locations. Under DL + TL1 conditions, the task lamp delivers light directly onto the desk surface along a predominantly horizontal path and at close range to the sensor. As a result, increases more substantially than , shifting into the recommended range and effectively normalizing the excessive baseline contrast observed under daylight-only conditions. By contrast, DL + TL2 configurations direct luminous flux toward the vertical wall behind the laptop, where interreflections redistribute this light more uniformly across the room. By the time this reflected light reaches the horizontal plane, a significant portion of its intensity has been attenuated, causing Eh_working desk to rise less than and driving ratios below unity despite some reduction in overall contrast.

However, these results must be interpreted in the context of the overcast sky model used in the experiment, which represents a worst-case condition characterized by highly uniform, diffuse daylight without direct sun penetration. Under such conditions, the existing daylight contribution to both the working desk and the surrounding field is relatively low yet evenly distributed. Consequently, TL2 primarily reinforces this diffuse lighting character rather than creating a strong task emphasis, making it difficult to achieve the illuminance ratio of 1.00–1.67 during measurements. In a clearer sky or higher-daylight scenario, the incoming daylight at the desk would likely increase disproportionately relative to portions of the ambient field, potentially allowing indirect configurations to approach compliance more readily. However, the present results indicate that, under overcast conditions, TL2 alone is insufficient to secure task dominance at the horizontal plane. These observations align with established ergonomic guidance indicating that conventional centralized ambient or broadly diffused illumination is inadequate for screen-based tasks and that localized task lighting is necessary to support productive activities in bedrooms while maintaining visual balance. In this specific dormitory setting, direct task lighting acts as a robust compensatory strategy under the most demanding daylight conditions, ensuring that the working desk is neither under-illuminated nor overwhelmed by ambient diffuse light. In doing so, it operationalizes the need identified in the Introduction to reconcile restorative bedroom lighting with the higher visual acuity demands associated with extended laptop use.

5.2 Neutral task-light CCT as a spectral bridge in warm rooms with cool screens

The analysis of mean ΔCCT values (Figure 4) demonstrated a clear spectral contrast between the task and ambient areas, with daylight-only conditions producing the highest mean ΔCCT (∼440 K). This result reflects a common mismatch in environments where cool daylight interacts with warm ivory room surfaces, while the cool laptop screen emits light in the CCT range of 5,000–6,500 K. Previous studies have shown that such spectral mismatches can lead to visual discomfort and increased eye strain, especially in screen-based environments requiring extended visual focus (Shahidi et al., 2021). In these scenarios, the absence of a mediating light source to bridge the tonal disparity between task lighting and ambient light significantly increases the tonal nonuniformity across the visual field, exacerbating visual fatigue during prolonged laptop use.

However, the introduction of tunable task lighting substantially altered the results. Direct task lighting (TL1 with CCTs of 3,000–4,000 K effectively reduced ΔCCT to approximately 202–260 K, acting as a spectral mediator between the cool laptop light and the warm room surfaces. This outcome confirms that intermediate CCTs—particularly around 4,000 K—closely align with neutral daylight while remaining warmer than the laptop’s cool light. As a result, the gap between the cool vertical emission from the laptop and the warm-reflecting surfaces of the room was significantly reduced, improving tonal consistency and achieving a more balanced visual environment.

These findings align with Hypothesis H2a, which proposed that warmer task lighting would reduce spectral contrast and facilitate tonal coherence across the workspace. Furthermore, they support prior experimental evidence suggesting that CCTs aligned with, or moderating room surface colors (e.g., 4,000 K in warm or neutral interiors) are effective in enhancing perceptual uniformity and visual comfort. Conversely, when task lighting was set to 3,000 K, the surrounding room lighting became even warmer, thereby widening the spectral gap between the cool laptop screen and the warm ambient surroundings. Similarly, cooler task lighting (5,000–6,500 K) increased the contrast by amplifying the cool dominance at the desk, creating a stark contrast with warm room tones. This pattern emphasizes the importance of spectral balance in achieving a visually comfortable environment, particularly in screen-based tasks.

Collectively, these results support the concept of “spectral unity” as a critical factor for achieving visual balance (Shahidi et al., 2021). By mediating the contrast between task lighting and ambient light, neutral-to-warm task lighting—especially around 4,000 K—ensures a coherent visual experience that reduces visual stress and enhances visual comfort. By contrast, task lighting configurations that either overly warm or cool the task area exacerbate spectral mismatches, undermining the tonal coherence required for effective screen-based work.

5.3 Color rendering fidelity and consistency for enhanced visual performance

The analysis of mean ΔCRI values (Figure 6) demonstrated the pivotal role of color rendering fidelity and CRI consistency in enhancing visual comfort and task performance during screen-based activities. The highest ΔCRI values were observed under daylight-only conditions and at high CCT task lighting (6,500 K), where a significant color mismatch occurred between the warm ambient environment and the cool task lighting. This substantial color mismatch created high color-fidelity contrast, which contributed to visual discomfort and increased eye strain. By contrast, configurations with warmer task lighting (3,000 K) produced the most uniform color rendering, as evidenced by the lowest ΔCRI values. This finding underscores that color rendering consistency, or CRI consistency, plays a crucial role in minimizing perceived discomfort and enhancing task clarity. These results align with existing literature on color perception and color fidelity in lighting design, which highlights the importance of uniform color rendering in reducing visual fatigue and improving cognitive performance (Yan et al., 2025; ISO 9241-3, 1992; WELL v02 L07, 2020.

The methodology employed in this study—which measured CRI values at multiple locations across the task area and ambient lighting—was effective in assessing the spatial consistency of color rendering. The results indicate that TL1 at 3,000 K was the most effective at achieving color fidelity and CRI consistency, reinforcing the idea that consistent lighting spectra contribute to a harmonious visual experience, thereby minimizing perceptual gaps between the task and ambient zones.

Furthermore, the CRI results address Q3 by demonstrating that color rendering quality at the working desk is primarily driven by CCT selection rather than by the task lighting configuration (direct vs. indirect). Daylight-only conditions and the DL + TL1 6,500 scenario exhibited the highest ΔCRI values, indicating significant color-fidelity mismatch between the cool laptop screen and warm-toned room surfaces. Conversely, the DL + TL1 3,000 scenario exhibited the lowest ΔCRI value (≈1.88), indicating that warm task lighting in a warm environment produces the most uniform color rendering between the task and ambient lighting, despite the increased spectral distance from the cool laptop screen. This observation underscores the importance of CCT tuning in achieving a visually balanced environment, where warm lighting can enhance color rendering consistency and spectral coherence.

Further analysis revealed that the task lighting configuration [whether direct (TL1) or indirect (TL2)] had a secondary role in determining color rendering consistency. Both direct and indirect configurations showed similar CRI values when paired with appropriate CCTs, suggesting that CCT plays the most significant role in achieving color rendering fidelity, while the lighting configuration primarily contributes to the distribution of light and the balance between task and ambient illuminance. This finding does not support Hypothesis H3b, which suggested that TL2 would yield better CRI consistency. The analysis showed that TL2 did not significantly enhance CRI consistency compared with TL1, as both configurations-maintained CRI values above the baseline standard (Ra ≥80). This suggests that the key factor in achieving optimal color rendering consistency is CCT selection rather than the lighting configuration itself.

5.4 Integrated evaluation of lighting scenarios and their practical applications

The integrated evaluation (Figure 8) synthesized findings from the three primary performance metrics: task-to-ambient illuminance ratios, ΔCCT, and ΔCRI. The results revealed that TL1 with warmer CCTs (3,000–4,000 K) offered the most balanced lighting scenario, consistently satisfying the EN 12464-1 recommendations for visual balance across all three metrics. This configuration demonstrated optimal performance in maintaining appropriate task-to-ambient illuminance ratios, moderate spectral contrast, and uniform color rendering. As such, it emerges as the most suitable lighting solution for multifunctional spaces, such as student dormitories, where both restorative and productive lighting functions are essential. These results directly support the integrated approach outlined in Section 1.4, which aimed to optimizing visual balance through a combination of ambient lighting and task-specific interventions.

The methodology of combining direct task lighting with ambient light and evaluating its impact across different times of the day provided a comprehensive understanding of how task lighting configurations influence visual comfort in a dynamic lighting environment. The results not only validate the need for task lighting configurations that align with the functional needs of multifunctional spaces but also challenge the initial assumption in Hypothesis H4 that TL2 would automatically yield superior visual balance. Although indirect lighting has been shown to be beneficial for glare control and spatial uniformity in other studies, the present analysis revealed that—in this particular dormitory geometry—TL2 was insufficient to meet the European Committee for Standardization (2002) lighting ratio standards. Specifically, indirect TL2 configurations tended to under-illuminate the task plane relative to ambient lighting, even when spectral and CRI metrics were acceptable. This finding points to the need for a direct-anchored solution that combines TL1 with spectral moderation to achieve a better balance of illuminance, spectral contrast, and color rendering consistency.

In the multi-criteria evaluation detailed in Section 4.4, the analysis showed that the DL + TL1 configuration, particularly with CCTs of 3,000–4,000 K, provided the most stable performance across the day. This configuration consistently maintained values within or close to the 1.0–1.67 target while also minimizing ΔCCT and ΔCRI values compared with daylight-only and high-CCT conditions. The combination of daylight with TL1 at these CCT values was found to restore task-plane dominance, reducing spectral mismatch between the cool digital emission from the laptop screen and the warm architectural finishes of the room. This aligns with the study’s original objective to develop lighting systems that support both restorative bedroom functions and productive screen-based work, demonstrating how task lighting at moderate CCTs mediates between cool screen emissions and warm room surfaces, thus enhancing visual comfort and supporting task performance.

However, the analysis also identified a critical nuance in the application of hybrid TL2 setups. Despite the potential benefits of indirect TL2 configurations for glare control and spatial uniformity, they were not sufficient to meet EN 12464-1-derived illuminance (European Committee for Standardization, 2002) ratio criteria in this specific geometry. Although indirect lighting improves spatial diffusion, it often results in under-illumination of the task plane, failing to provide the adequate contrast needed for visual clarity and task performance. This challenges the assumption that indirect lighting configurations would automatically lead to better overall contrast reduction and more uniform lighting. In this case, the optimal configuration emerged as one that was direct-anchored but spectrally moderated, with TL1 at warmer-to-neutral CCTs proving more effective in maintaining visual balance across illuminance, spectral coherence, and CRI consistency.

These findings should also be interpreted within the boundary conditions of the experimental setting, namely, a compact student dormitory bedroom with fixed geometry, warm ivory surfaces, a north-facing window, and predominantly overcast daylight conditions. These conditions likely influenced the measured task-to-ambient illuminance ratio, ΔCCT, and ΔCRI. Under overcast skies, daylight is diffuse and relatively uniform, making direct task lighting more effective in restoring task-plane dominance. Under clearer skies or stronger daylight penetration, task illuminance may increase naturally, and the relative performance of indirect lighting may differ. Similarly, rooms with different window orientations, surface finishes, dimensions, or luminaire positions may produce different illuminance ratios and spectral interactions. Therefore, the recommendation for direct task lighting at 3,000–4,000 K is most applicable to compact, warm-surfaced bedrooms under diffuse daylight conditions and should be validated across broader climatic, daylighting, and spatial contexts.

5.5 Practical lighting recommendations for student dormitories: Bridging comfort and productivity in multifunctional spaces

6 Conclusion

The study has several limitations that constrain the generalizability of these findings. This study was conducted in a single room with fixed geometry and warm finishes under predominantly overcast daylight conditions. It relied solely on objective photometric and colorimetric metrics, without incorporating subjective assessments of visual comfort or performance data. The experimental protocol used a white laptop screen at maximum brightness rather than realistic, content-rich displays, and the analysis focused on short-term visual balance rather than long-term non-visual or circadian effects. Despite these limitations, the study contributes a metric-driven framework for assessing visual balance in compact multifunctional spaces, demonstrating how combined thresholds for , ΔCCT, and ΔCRI can differentiate lighting scenarios that meet or fall short of performance standards and offering actionable guidance that prioritizes adjustable, direct lighting at 3,000–4,000 K over purely indirect solutions in warm-surfaced dormitories.

Future research should validate these findings in a wider range of room geometries, surface palettes, and daylight conditions; incorporate user-based evaluations of comfort, glare, and performance; consider more realistic, multi-device, mixed-content screen use; and extend the temporal scope to evening and pre-sleep periods with explicit circadian metrics. Further studies should also explore multi-objective optimization approaches that jointly address energy efficiency, visual balance, and non-visual outcomes to support more comprehensive design and policy recommendations. Although the present study emphasizes localized workstation balance using task-to-ambient contrast metrics, future studies may further contextualize these findings using broader ambient luminous-environment metrics such as Mean Room Surface Exitance (MRSE), as proposed by Cuttle and later discussed by Duff, to evaluate how perceived room brightness interacts with localized screen-task lighting conditions.

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