Lighting Design for Visual Comfort and Energy Efficiency Considerations: A Patient Room Case Study

Glare is a kind of physiological phenomenon that influences occupants’ visual comfort. Discomfort glare scenes in comparison to other levels of glare have been difficult to estimate and need accurate and reliable metrics. In contemporary architecture, the glass façade is so popular since it can remarkably minimize energy consumption in buildings and maximize daylight utilization as a natural energy. However, it is necessary to consider occupants’ visual discomfort due to the daylighting glare risks during the initial stage of design. Since the measured glare metrics should have an acceptable correlation with the human subject data study, the agreement on the glare indices is complicated. This paper presents a comparison between subjective and simulation-based analysis of discomfort glare metrics in offices with a light shelf system. The discomfort glare metrics considered in this study include Daylight Glare Index (DGI), CIE Glare Index (CGI), Visual Comfort Probability (VCP), Unified Glare Rating (UGR), and Daylight Glare Probability (DGP). The parallel comparison was conducted by using simulation and questionnaire surveys to determine which criteria are more useful under different conditions. According to the findings, DGP yields the most reliable results in different levels of glare based on the subjective analysis and VCP has the lowest accuracy in each stage. UGR also has the highest accuracy rate for evaluating perceptible glare, DGI is applicable for assessing imperceptible glare, and CGI can be an acceptable index for approximating intolerable glare. The study results significantly reduce the complexity of the problem and can provide useful guidance for designers to select the most reliable glare metric based on climatic conditions.

Educational buildings are recognized as one of the largest consumers of electrical energy. Inadequate lighting can also have negative physical and psychological effects on these environments. Therefore, optimal lighting design that meets electrical energy needs while providing visual comfort is essential. Reducing glare, primarily caused by artificial lighting in educational environments, is particularly important. Glare can lead to discomfort and eye fatigue, adversely affecting learning performance. To measure and assess this phenomenon, the “Unified Glare Rating (UGR)” metric is employed, which helps designers accurately evaluate the level of glare caused by lighting. This paper examines the parameters of height and surface reflectance as variable factors to achieve an optimal design that reduces lamp demand and minimizes glare, using a three-phase methodology: (1) using Dialux software, two primary scenarios—varying heights (2.5 and 3 m) and reflectance coefficients (ceiling, walls, floor)—were examined, (2) across 100 simulations followed by correlation and regression analyses to assess the effect of each reflectance coefficient (ceiling, walls, floor) on illuminance and the UGR, and (3) energy performance evaluation. Results demonstrate trade-offs: reducing lamps from 15 to 9 lowered energy use by 40% but increased UGR from 13 to 18 (approaching the discomfort threshold of 19), while 12 lamps achieved a balance—20% energy savings, a UGR of 14, and uniformity of 0.67. Surface reflectance emerged as critical, with high-reflectance ceilings (≥85%) and walls (≥80%) contributing 50.9% and 32% to illuminance variance, respectively. This study concludes that multi-parameter optimization—integrating height, lamp quantity, and reflectance—is essential for energy-efficient classroom lighting with acceptable glare levels, providing actionable guidelines for urban educational environments constrained by artificial lighting dependency.

ABSTRACTGlare which affects comfort or causes distraction is known as discomfort glare and glare which affects the ability to see any object is known as disability glare. Discomfort glare is mainly caused by artificial lighting of the workplace. Discomfort glare can be measured by using Visual Comfort Probability (VCP) or Unified Glare Rating (UGR). This paper discuses the discomfort evaluation methods and presents the calculations of UGR of a specific workplace. The discomfort glare is calculated by using DIALux lighting simulation software, Techno Team LMK measuring system and by using developed Python program model. The results are compared and verified with the feedback received from occupants/users of that workspace. A comparison of the UGR values determined by the DIALux lighting simulation software, LMK measurement system and subjective estimation shows that the values obtained by LMK measurement system are more accurate and are matching with the feedback received from occupants of the workspace.

We review the discomfort glare evaluation systems of the Illuminating Engineering Society of North America (IESNA), Visual Comfort Probability (VCP), and that of the International Commission on Illumination (CIE), Unified Glare Rating (UGR), as they apply to interior electric lighting. We provide an overview of the history and research behind them and an extensive bibliography.The current IESNA Handbook states that the VCP is very limited in applicability to modern lighting systems, and was validated for lensed fluorescent systems only. The CIE's UGR system has been shown to be a good predictor of human responses for lensed fluorescent systems. Recently, the CIE has proposed extensions to the UGR discomfort glare model, which are applicable to most modern lighting systems, including small, large, and complex systems. We provide a review of these extensions and the research behind them. There are many similarities between VCP and UGR and only minor differences, and so we recommend that research be undertaken to validate the UGR's extensions to small, large, and complex systems.

Calculation of the Unified Glare Rating based on luminance maps for uniform and non-uniform light sources

Energy-Efficient Office Renovation

Energy-Efficient Office Renovation

The design of an indoor lighting system for a sustainable building should comply with the recommended maximum limit of lighting power density. The occupants’ visual comfort and visual performance are to be ensured by complying with some mutually conflicting lighting design parameters, such as maintained average illuminance, overall uniformity, and maximum unified glare rating, to the recommended limits. Judicious balance among these multiple conflicting design parameters is a practical design problem. This article aims to address these aspects of indoor lighting design by applying a particle swarm optimization (PSO) algorithm in a developed lighting computation program. The objective function is formulated with maximum or minimum limits for the design parameters recommended by international standards. The effectiveness of the developed program is evaluated by designing an indoor lighting system with commercially available luminaires for an office space that ensures optimized visual comfort, energy efficiency, and initial cost. Optimized results are validated by DiaLux simulation and a maximum deviation of 2.27% is found. Thus, the results show good agreement with DiaLux simulation and significant improvement in the uniformity of illuminance (0.90) compared to the recommended minimum value (0.70) and in discomfort glare (16) compared to the recommended allowable maximum value (19). The developed program establishes the usefulness of the PSO algorithm to optimize the luminaire layout for an indoor general lighting scheme.

This paper studies discomfort glare in indoor LED lighting systems and proposes a method reducing UGR calculations. There are several methods for expressing discomfort glare, among which the unified glare rating (UGR) method is one of the most popular. It is safe to indicate that the UGR method was introduced before LED lighting became popular in indoor applications. Thus, the UGR method is not versatile currently. In this paper, key limitations of the UGR method are discussed. A method for reducing UGR calculations based on UGR tables for both LED luminaires with diffusers (uniform luminous intensity distribution) and with lenses is proposed. The method is mathematically discussed and its applicability for luminaires is discussed. Also, the luminaires are put through a test and the results from the tests are presented and the feasibility of the method separately from mathematical proofs is examined. The proof and case studies both indicate that the method can be used accurately for luminaires with diffusers. They also illustrate that the accuracy of applying the proposed method to the LED luminaires with lenses is not satisfactory. Simulations are carried out using DIALux lighting design software.

Energy efficiency considerations recently gained attention due to ecological aspects, that is to say lowering CO 2 emissions and reducing energy consumption. Furthermore, it is important to assess energy efficiency improvements from an operator's point of view, since energy costs are increasing and providing ubiquitous high speed mobile access may scale up the operators' operational expenditure. One of two promising approaches to enhance a network's operation regarding energy efficiency is to utilize smaller micro cells within one large macro cell. Another approach is to regard macro base stations as coverage providers for areas in between micro cells, while reducing their maximum transmit powers to a minimum. In this paper we investigate on the energy efficiency of a heterogeneous OFDM-based mobile network in the downlink taking into account the co-channel interference based on varying traffic demand per area. Furthermore, we carry out an assessment of potential energy savings of the two approaches mentioned above. For a sufficiently large traffic demand, increasing deployment densitiy through additional micro sites may maximize a network's energy efficiency. In that case the network operates at a load of less than 50 %. Moreover, a further gain of energy efficiency of about 20 % can be achieved due to macro site transmit power reduction while still providing coverage.

In recent years, there has been a heightened emphasis improving visual comfort and energy efficiency. Various solutions have been explored to achieve high-performance design. Shading devices play a crucial role in enhancing building performance by redusing solar gains, excessive daylight, and improving both energy efficiency and occupants' visual comfort. This research aims to investigate the effect of facade geometry on visual comfort and energy consumption in four different climates of Iran and categorize each variable based on effectiveness for each location. Parametric office modeling was done by using Grasshopper and Rhino software. Then, the effect of the facade on the interior lighting and energy consumption was analyzed by Radiance, Daysim, and EnergyPlus calculation engines. The Non-Dominated Sorting Genetic Algorithm (NSGA-II) was selected to optimize solutions, minimize energy consumption, maximize useful daylight illuminance, and view quality. In addition, the methodology was used to explore the framework for optimizing office facade design in Iran's diverse climatic zones. The simulation results indicate that window-to-wall ratio and inclined wall were essential for balancing daylighting performance and energy consumption. This research stated that using a self-shading design could increase the quality of view up to 75% while reducing energy consumption and the risk of glare. Results proposed a design framework to improve visual comfort and save energy. The rotating façade's wall 10°-30° reduced cooling energy demand and energy usage intensity in selected models. So, an inclined wall could be an efficient shading device to improve building's performance in Iran.

LEED is one of the most widely adopted building benchmarks globally, and it encompasses multiple rating criteria for performance. However, such criteria typically focus on reducing energy consumption and may disregard providing a high level of occupant satisfaction. LEED focuses on a desk height evaluation of Spatial Daylight Autonomy and Annual Sunlight Exposure to predict the daylight availability and probability of glare, respectively, which may disregard an occupant’s visual comfort at eye level. This paper proposes a more comprehensive approach to daylighting performance evaluation in a commercial office space that incorporates Annual Glare – vertical-eye level glare evaluation, in addition to Spatial Daylight Autonomy and Annual Sunlight Exposure. A comparison between Annual Sunlight Exposure and Annual Glare is established to understand the criteria missing in LEED that evaluates discomfort glare and improves the visual performance and comfort of the occupants significantly.

Leadership in Energy and Environmental Design (LEED) is one of the most widely adopted building benchmarks globally, and it encompasses multiple rating criteria for performance (Owens et al., 2010). However, such criteria typically focus on reducing energy consumption, and may disregard providing a high-level of occupant satisfaction (Wilder et al., 2019). LEED focuses on a desk height evaluation of Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE) to predict the daylight availability and probability of glare respectively (IES LM-83-12, 2012), which may disregard an occupant’s visual comfort at eye level. This paper proposes a more comprehensive approach to daylighting performance evaluation in commercial office space that incorporates Annual Glare - vertical-eye level glare evaluation, in addition to sDA and ASE. A comparison between ASE and Annual Glare is established to understand the criteria missing in LEED that evaluates discomfort glare and improves the visual performance and comfort of the occupants significantly.

This study is based on a general interior lighting installation and discusses the relation between veiling luminance and the unified glare rating. Through curve fitting and a derived formula, a transfer function between veiling luminance and the unified glare rating is generated. This result connects disability glare and discomfort glare within a finite range, where the relation between them is almost linearly dependent. This transfer function has a high accuracy as shown by a comparison between the calculated results and the original data, and is the first to provide a connection between disability glare and discomfort glare.

The aim of the study was to analyze discomfort glare sensation in subjects aged 50 years and more in comparison with younger subjects (i.e. younger than 35 years of age). The experiments were performed on a computer workstation placed in controlled lighting environment where 2 discomfort glare conditions were modeled. Each participant performed for about 1 h specially designed visual tasks, including the tests with Landolt's rings presented on the screen by a computer program. The glare evaluation method consisted of subjective evaluation of discomfort glare on the semantic glare rating scale, tests of mesopic contrast and glare sensitivity, subjective assessment of lighting quality and asthenopic symptoms. The time needed to perform the task and the number of mistakes were also recorded. The subjective evaluation of glare was compared with the Unified Glare Rating (UGR) index calculated by the DIALux simulation program. A higher percentage of the younger group subjects assessed glare after the experimental session as uncomfortable and intolerable than in the 50+ group, who more often assessed glare as acceptable. The assessment of discomfort glare in the younger group corresponded to higher UGR value compared to UGR value calculated by DIALux. In the 50+ group, such correlation was found only for lower discomfort glare (UGR = 19). The results showed that younger participants more frequently suffered from visual fatigue and assessed lighting as less comfortable. However, the mesopic glare sensitivity increased significantly after the experiments only in the 50+ group under both glare conditions. The obtained results showed that discomfort glare sensation changes with age. The younger population seems to be more sensitive and demanding than the older one in relation to discomfort glare limiting, in spite of the lack of significant objective measures of fatigue. The exposure of the elderly to bigger discomfort glare could adversely affect the objective measures of fatigue like mesopic glare sensitivity and visual performance.