Toward an Optimal Lighting Range: Insights into Visual Comfort and Occupant Well-being in Offices

Toward an Optimal Lighting Range: Insights into Visual Comfort and Occupant Well-being in Offices

Dr. Chaitali Trivedi

The Maharaja Sayajirao University of Baroda

Abstract – Visual comfort plays a crucial role in the effectiveness and well-being of office occupants, as lighting directly affects task performance. Consequently, the presence, quality, and intensity of light are important considerations in both architectural design and operational planning. This study examines occupant satisfaction with lighting conditions in office workspaces using a three-pronged methodological approach.

First, subjective data were collected through interviews with office occupants to assess perceived visual comfort. Second, an objective evaluation was conducted via a questionnaire distributed using random sampling techniques, wherein participants rated their satisfaction with lighting levels on a scale from 20% to 100%. Third, the collected responses were analysed using an independent samples t-test to verify the mean satisfaction range.

The findings support the development of a visual comfort rating scale for office buildings in the Indian context. Surveys were conducted across 15 office buildings, encompassing 513 participants under three distinct lighting conditions. Results indicated that 95% of respondents reported satisfaction within an illuminance range of 150 to 300 lux (±50 lux). However, the study also found that many office environments do not meet this comfort standard. A common issue is the occurrence of glare due to over-illumination from fully glazed facades, which adversely affects both energy efficiency and occupant well-being.

Keywords: keyword 1; Visual Comfort 2; Occupants Wellbeing 3; illumination 4; post occupancy evaluation 5; Office Buildings

1. INTRODUCTION

   Every component of human health is profoundly affected by lighting. It has an impact on our psychological and physiological health [1]. Individual differences in lighting preferences have been documented [27], and they are typically examined to lighting stimuli [6, 8, 9]. Contemporary research emphasizes the critical role of workplace lighting in determining employees satisfaction, productivity, and overall health outcomes [10] .

   The interplay between light and work has long been a subject of investigation, given that one of the primary functions of lighting in work environments is to facilitate tasks efficiently, accurately, and comfortably. The work environment encompasses a range of physical conditions, including lighting, that influence the quality and ease of work performance [11]. Visible light, in particular, is a core environmental factor. When improperly designed, either insufficient or excessive intensity can become a source of discomfort, contributing to fatigue, irritability, or even short-term psychophysical strain [12]. Beyond merely ensuring visibility, lighting conditions can impact mood, circadian rhythms, and physiological health. Inadequate or excessive lighting may result in glare, headaches, eye strain, poor posture, and, in extreme cases, more serious visual impairments [13, 14]. Although substantial effort has been dedicated to creating well-lit architectural spaces, the ability to clearly define the parameters of a “well-lit space” remains underdeveloped [15]

   Visual comfort is influenced by multiple factors, including light composition, glare and spatial elements such as working plane height, spatial configuration, functional use, and availability of outdoor views [16]. Both natural and artificial lighting play critical roles in shaping the experience of visual comfort [17]. The benefits of light are becoming increasingly clear, and suitable illumination is essential for occupants satisfaction.

   Visual comfort is typically understood as a subjective response to the intensity and quality of light within a space at a specific time [18]. Two theoretical frameworks commonly guide the assessment of visual comfort: the widely adopted non-annoyance approach, which emphasizes the absence of discomfort, and the well-being approach, which focuses on the positive effects of lighting on user satisfaction [19]. This study employs the well-being approach, using perceived satisfaction as a primary indicator of visual comfort.

   The primary source of illumination in the workplace is natural light. Excessive light and visual discomfort are the drawbacks, even if having a view and being close to windows are always desirable and provide health benefits [20]. Artificial lighting is typically regarded as the most used type of lighting in offices across the globe because of its dependability, variety, and alternatives. However, using artificial illumination excessively when there is no natural lighting poses a health danger to the workers. It can be problematic to be out of the sun during working hours, particularly for extended periods [14]. Understanding the importance and constrain of both types of lighting, in this study, a survey was conducted under three different lighting conditions to assess the perceptions of the lighting conditions held by employees. The study is an attempt to understand illumination levels against visual comfort in

   workspaces and thereby derive a range of illuminance where occupants feel comfortable through the method of post-occupancy evaluation.

   This study establishes that the perceived comfort range for office lighting lies between 150 300 lux, with standard deviation of ±50 lux, challenging the higher levels recommended by conventional standards

2. MATERIALS AND METHODS

   This study aims to understand the range of visual comfort for working in offices and the relationship between light sources and visual comfort. Assessing occupants’ responses to lighting often involves measuring user satisfaction through subjective, objective, or combined methods. While some studies [10], [2123] incorporate both approaches in controlled settings, comparative research between subjective and objective assessment methods remains limited. Nonetheless, user satisfaction is still one of the most effective indicators of lighting adequacy and comfort [10]. Therefore, this study uses both techniques to evaluate occupants satisfaction levels based on the illumination range. The comfortable visual range is identified by comparing results from both methods.

   To gauge users perceptions, a structured questionnaire was designed alongside quantitative measurements of illumination levels using a lux meter (TESTO 540). The study covered 15 office spaces in different cities across Gujarat, India. A total of 513 occupants were surveyed under varied conditions. Measurements were taken at the work plane height (750 mm above the floor) across a grid marked at 1-meter intervals on both the X and Y axes of the office layout (Annexure 1). The visual comfort range is assessed in three distinct ways, as detailed in sections 2.1, 2.2, and 2.3.

   1. Objective Evaluation

      Objective evaluation of illumination levels was carried out by measuring the lux levels using a light intensity meter. Illumination data is recorded under three lighting conditions: natural daylight only, artificial lighting only, and a combination of both, as shown in Figure 1. Occupants satisfaction levels against available illumination is registered.

      Figure 1. Offices surveyed under different lighting conditions Source: Author

      1. 1. 1. Readings in the presenc of Daylight only (DL)

               Data highlights that 90% of the satisfied occupants were comfortable when the illumination received at their respective work plane ranged between 101 lux to 350 lux, whereas the majority of the dissatisfied occupants (88%) received the illumination between 0 150 lux at their work plane. Data on satisfied and dissatisfied occupants against available illumination in the presence of daylight is as shown in Table 1 for objective evaluation

               Table 1. Illumination levels noted in the presence of daylight only during the objective evaluation

               	Illumination (lux) received at the work plane against the user’s perception
               No. of Occupants	0-50	51-100	101-150	151-200	201-250	251-300	301-350	351-400	401-450	451-500	501-550	551-600	601-1000
               Dissatisfied	82	78	36	1	0	2	2	2	5	2	1	3	8
               Satisfied	0	3	57	42	45	38	25	11	4	1	1	0	2
               Total	82	81	93	43	45	40	27	13	9	3	2	3	10

            2. Readings in the presence of Artificial light (AFL)

               Data highlights that 90% of the satisfied occupants were comfortable when the illumination received at their respective work plane ranged between 101 lux to 300 lux, whereas the majority of the dissatisfied occupants (72%) received the illumination between 0 100 lux at their work plane. Data on satisfied and dissatisfied occupants against available illumination in the presence of artificial light is as shown in Table 2 for objective evaluation

               Table 2. Illumination (lux) levels noted in the presence of artificial light only during the objective evaluation

               	Illumination (lux) received at the work plane against the user’s perception
               No. of Occupants	0-50	51-100	101-150	151-200	201-250	251-300	301-350	351-400	401-450	451-500
               Dissatisfied	150	122	12	10	3	7	6	27	18	21
               Satisfied	0	6	32	47	36	32	8	3	0	0
               Total	339	28	38	49	36	33	8	5	2	2

            3. Readings in the presence of a combination of Daylight and Artificial light (DL+AFL)

      Data highlights that 53% of the satisfied occupants were comfortable when the illumination received at their respective work plane ranged between 101 lux to 300 lux. Low dissatisfaction among occupants was observed while working in a combined lighting condition. In some instances, it was observed that combined light conditions resulted in access light with illumination levels beyond 550 lux. This resulted in discomfort and high dissatisfaction among occupants. Data on satisfied and dissatisfied occupants against available illumination in the presence of a combined lighting condition (daylight with artificial light) is as shown in Table 3 for objective evaluation. The readings under all three conditions showed a similar range of satisfaction levels, as shown in Figure 2

      Table 3. Illumination levels noted in the presence of both daylight and artificial light during the objective evaluation

      	Illumination (lux) received at the work plane against the user’s perception
      No. of Occupants	0-50	51-100	101-150	151-200	201-250	251-300	301-350	351-400	401-450	451-500	501-550	551-600	601-1000
      Dissatisfied	0	6	1	3	5	2	1	0	8	8	8	13	35
      Satisfied	0	0	4	18	33	21	16	13	9	4	2	1	9
      Total	0	6	5	21	38	23	17	13	17	12	10	14	44

      Figure 2. Illumination levels in the presence of (a) Daylight (DL), (b) Artificial light (AFL), and (c) combination of Daylight and Artificial light (DL+ALF) only during objective evaluation

   2. Subjective Evaluation

      Subjective evaluation was done based on a pre-structured questionnaire. While the occupants filled out the questionnaire, readings were taken on an individuals work plane once when the lights were ON (AFL, DL+AFL) and once after turning OFF (DL) the lights. The questionnaire was used to gauge the users perception of their working environment and visual comfort experienced while working. Occupants’ perception is marked on a scale of 20% to 100%, indicating their satisfaction level about visual comfort as shown in Figure 3.

      Figure 3. Illumination levels in the presence of Daylight (DL), Artificial light (AFL), and a combination of Daylight and Artificial light (DL+ALF), only during subjective evaluation

      Data highlights that the majority of the satisfied occupants (73.8%) surveyed under the lighting OFF condition received illumination ranging from 101- 350 lux, as reflected in Figure 4a. Similarly, the majority of the satisfied occupants (73.5%) surveyed under the lighting ON condition received illumination ranging from 101- 300 lux, as shown in Figure 4b

      (a) (b)

      Figure 4. Illumination levels in the presence of (a) Daylight (DL) and (b) Artificial light (AFL) during Subjective evaluation

   3. Statistical Evaluation

      Further, for the analysis of the data collected during the survey independent t-test was used with the hypothesis (Ho): Average illuminance among the satisfied group of people is equal to average illuminance among the dissatisfied group of people. The test is to check if there exists a significant difference between two sets of variables, here satisfaction (S) and dissatisfaction (DS) with regard to lux levels.

      Out of 461 individuals surveyed under daylight conditions, 234 reported being satisfied, with a recorded mean illuminance of 246 lux and a standard error of the mean () of 10.37. Using a 95% confidence interval (2 = 20.75), the range of illuminance levels corresponding to ocupant satisfaction under daylight alone lies between 225.25 lux and 255.95 lux.

      In settings illuminated solely by artificial light, 160 out of 176 participants expressed satisfaction. The mean illuminance measured was 210 lux, with a standard error () of 9.3. Applying a 95% confidence interval (2 = 18.6), the corresponding satisfaction range spans from 191.4 lux to 228.6 lux.

      For environments combining daylight and artificial lighting, 123 out of 212 respondents indicated satisfaction. The mean illuminance level observed was 234 lux, with a standard error () of 18.4. Accordingly, the 95% confidence interval (2 = 36.8) indicates that illuminance levels between 197.2 lux and 270.8 lux are associated with a high likelihood of occupant satisfaction under combined lighting conditions.

      (a) (b) (c)

      Figure 5. Illumination levels in the presence of (a) Daylight (DL), (b) Artificial light (AFL), and (c) combination of Daylight and Artificial light (DL+ALF) during statistical evaluation for satisfied occupants.

      Among the 461 individuals surveyed under daylight-only conditions, 227 reported dissatisfaction. The mean illuminance level observed was 121 lux, with a standard error () of 10.89. Based on a 95% confidence interval (2 = 21.78), the corresponding range of illuminance associated with dissatisfaction falls between 99.2 lux and 142.78 lux.

      In the case of artificial lighting alone, 16 out of 176 participants expressed dissatisfaction. The mean illuminance level observed was 210 lux, with a standard error () of 35.9. This results in a 95% confidence interval (2 = 71.8), indicating a dissatisfaction range between 138.2 lux and 314.8 lux.

      For environments illuminated by a combination of daylight and artificial lighting, 89 out of 212 respondents were dissatisfied. The mean illuminance level observed was 542.55 lux, with a standard error () of 26.3. With a 95% confidence interval (2 = 52.6), the illuminance range associated with dissatisfaction lies between 489.95 lux and 595.15 lux.

      (a) (b) (c)

      Figure 6. Illumination levels in the presence of (a) Daylight (DL), (b) Artificial light (AFL), and (c) combination of Daylight and Artificial light (DL+ALF) during statistical evaluation for dissatisfied occupants.

3. Results

   This section is divided into three parts, where the first part derives the visual comfort range from the occupants’ satisfaction data of working in office buildings. The second part highlights the illumination levels where the majority of the occupants were dissatisfied. This part also discusses the reasons observed during the study for inappropriate illumination levels. The latter part summarises the overall lighting conditions observed during the study and the results of the hypothesis from statistical analysis.

   1. Visual Comfort Range

      Illumination from 101 lux to 300 lux was derived as a visual comfort range for working in an office building using both subjective and objective evaluation, as shown in Figure 7. This contradicts the recommended lighting levels prescribed by the Bureau of Indian Standards (BIS – IS 3646 Part 1), CIBSE, and European Standard EN 12464-1, which recommends 300-500 lux levels for general office work.

      Illumination range of Satisfied

      50 Occupants (Subjective Evaluation)

      NO OF OCCUPANTS

      Illumination range of Satisfied Occupants (Objective Evaluation)

      ILLUMINATION (LUX) DL DL+AFL AFL

      ILLUMINATION (LUX) DL AFL

      (a) (b)

      Figure 7. Illumination range of satisfied occupants under (a) subjective and (b) objective evaluation.

      The results were further cross-verified using a t-test. Illumination from 215 lux to 320 lux was derived as a visual comfort range from the statistical analysis. The visual comfort range from all the evaluations is as shown in Figure 8

      		Visual Comfort range of Illumination (lux)
      Evaluation	Light Condition	0-50	51-100	101-150	150-200	201-250	251-300	301-350	351-400	401-450	451-500
      Objective	DL
      	AFL
      	DL +AFL
      Subjective	Lights OFF
      	Lights ON
      Statistics	DL
      	AFL
      	DL +AFL

      Figure 8. Visual Comfort Scale comparison derived using techniques under different lighting conditions.

   2. Visual Discomfort

      The maximum number of occupants who were dissatisfied while working received illumination ranging from 0 to 150 lux. It was further observed that out of 959 readings noted where people were dissatisfied, 740 occupants received illumination between 0-150 lux as shown in Figure 9, which adds up to 77% of the total dissatisfied readings.

      Figure 9. Illumination range of dissatisfied occupants under (a) objective and (b) subjective evaluation.

      The results show that most of the dissatisfaction levels noted were due to low illumination received at the working plane. Further inquiry highlighted two reasons for low illumination, as discussed below

      1. Inadequate light

         It was observed that many areas in the plan (office layout) did not receive adequate sunlight as a result of improper spatial planning or deep office plans. In pursuit of views and hierarchy, single-occupied offices and cubicles were often placed near the building façade, whereas shared cubicles and workstations were placed in the central core. Shared cubicles and workstations are the areas where the maximum number of occupants work. This affects the productivity among workers. The distribution of artificial light was also not designed properly. Placement of artificial light did not take into account the density of people working; instead, it was placed randomly in a space without relevance to furniture placement. Occupants reported well-being problems like reduced efficiency of task performance, eye fatigue, dry or watery eyes, and daytime drowsiness.

      2. Access light

It was observed that most of the office buildings had a full glazed façade. This resulted in the access light leading to glare while working. To reduce excess illumination face was covered with blinds and sometimes with paper, which resulted in low illumination levels. Once the blinds were put on, the spaces often resulted in a dark and unevenly lit area. Full glazed facades are the prime reason for improper illumination levels, which affect both energy efficiency and occupants’ well-being. Occupants reported blurred vision, headaches, migraines, tired, itchy, or burning eyes, decreased focus, attention span, and cognitive performance. This was problematic, especially for screen-based and precision work.

For the statistical evaluation t-test was performed on the collected data to check if there exists a significant difference between the two sets of variables, here satisfaction (S) and dissatisfaction (DS) with regards to lux levels. It is a two-tailed test because the hypothesis involves the phrase different and no order of the means is specified. The value of sig. (2-tailed) for all the cases (Dl, AFL, DL+AFL) was found to be 0.00, which is less value of =0.05; hence, the null hypothesis that the variables of the two groups are equal is rejected. This implies that there is sufficient evidence to conclude that there exists a difference between the mean number of Satisfied (S) and dissatisfied (DS) occupants, and the difference is significant.

It is also observed that of all the readings reported, more than 50% occupants were dissatisfied with the illumination levels in their working environment. This highlights that most of the offices are not designed with proper lighting conditions. The combination of daylight and artificial light showed the highest satisfaction levels among all three lighting conditions, as shown in Figure 10.

Figure 10. Ratio of satisfied occupants versus dissatisfied occupants under (a) daylight only (b) artificial light only (c) combined lighting condition (daylight and artificial light)

4 Discussion

This study establishes a comfort range of 150 to 300 lux (±50 lux) as optimal illumination for occupants in an Indian office setting, which is lower than conventional standards, like BIS, IEE, and CIBSE. Through a combined methodology of subjective evaluation, objective evaluation of lux measurements, and statistical analysis, the study confirms that lighting significantly influences visual comfort. Beyond visual comfort, it also revealed strong links between lighting quality and occupant well-being.

The study highlights the importance of user-centric lighting design, which considers task type, spatial layout, and facade treatment. The prevalent mismatch between design intent and real-world lighting performance. The results show evidence of a high dissatisfaction rate and emphasize the need for integrated lighting strategies, improved spatial planning, and post-occupancy evaluations in the design process. Improper spatial layouts, such as placing shared workstations in deep plan cores away from facades, result in uneven light distribution, with many areas receiving sub-optimal natural light. Offices with full glazed facades, while intended to maximize daylight and aesthetics, often caused glare and visual discomfort, forcing occupants to close blinds or use makeshift arrangements. This finally results in under-illuminated spaces. The combination of natural daylight and artificial lighting showed the highest satisfaction rates, underlying the value of balanced, layered lighting strategies that can adapt to changing conditions and user preferences throughout the day. Occupants working in lighting conditions below 150 lux reported various symptoms indicating compromised health and performance, such as visual strain, cognitive fatigue, and headaches.

The study thus argues for a well-being-centric approach to lighting design in the office environment, one that balances qualitative standards with quantitative user experience, supports mental and visual health, and fosters a more productive and satisfying work environment. This study advocates for a contextual redefinition of lighting norms, one that reflects real user experiences and specific configurations of Indian office buildings. Future design and policy frameworks must integrate post-occupancy feedback, context- specific data, and adaptive lighting systems to create healthier workplaces

Supplementary Materials: The following supporting information can be downloaded at: https://drive.google.com/file/d/1pzsjL9ONlHXlq6ZI7enUdY9iF3ITUMYh/view?usp=sharing

Funding: This research received no external funding.

Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement: data supporting reported results are provided in supplementary material which can be accesses through following link https://drive.google.com/file/d/1pzsjL9ONlHXlq6ZI7enUdY9iF3ITUMYh/view?usp=sharing

Acknowledgments: I would like to acknowledge Prof. Rajan Rawal for this support and guidance. The author have reviewed and edited the output

and take full responsibility for the content of this publication.

Conflicts of Interest: The author declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:

DL Daylight

AFL Artificial Light

DL+AFL Combination of daylight and artificial light S Satisfied

DS Dissatisfied

Appendix A

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