Enhancing Classroom Lighting Quality in Tehran Through the Integration of a Dynamic Light Shelf and Solar Panels

Abstract

Numerous studies have demonstrated that appropriate use of daylight in educational spaces significantly enhances students’ health and academic performance. However, classrooms in Tehran still suffer from considerable daylighting challenges. In many cases, desks near windows are exposed to excessive brightness, while areas farther from the windows lack adequate illumination. This often leads to the use of curtains and artificial lighting, resulting in higher energy consumption and potential negative impacts on student learning. Light shelf systems have been proposed as effective daylighting solutions to improve light penetration and distribution. According to previous research, three key parameters—geometry, depth, and surface reflectance—play a critical role in the performance of light shelves. However, prior studies have typically focused on improving one or two of these parameters in isolation. There is a lack of research evaluating all three parameters simultaneously to determine season-specific configurations for optimal performance. Addressing this gap, the present study investigates the combined effects of light shelf geometry, depth, and reflectance across different seasons and proposes a system that dynamically adapts these parameters throughout the year. In winter, the system also integrates photovoltaic panels to reduce glare and generate electricity for its operation. Simulation results indicate that the proposed system leads to a 21% improvement in Useful Daylight Illuminance (UDI), a 65% increase in thermal comfort, and a 10% annual reduction in energy consumption. These findings highlight the potential of the proposed system as a practical and energy-efficient daylighting strategy for educational buildings in sunny regions such as Tehran.

1. Introduction

A significant portion of every individual’s life is spent in schools and classrooms. Therefore, paying attention to visual and thermal comfort in educational spaces is of great importance. Numerous studies have been conducted on the impact of daylight on students’ mental health and learning, demonstrating that students perform better and achieve higher learning levels in classrooms with natural light [1]. Despite these findings, major lighting issues persist in educational spaces. One of the main challenges is the lack of uniformity and insufficient light at the back of the classroom. In most classrooms, desks near windows receive excessive light, causing glare, while the back of the classroom lacks adequate illumination. Consequently, curtains are often drawn, and artificial lighting is used, leading to increased energy consumption and a significant reduction in students’ performance [2]. Moreover considering recent climate changes and the rising energy consumption, it has become increasingly important to seek solutions that reduce energy use and enhance thermal comfort in buildings [3,4,5,6].

A light shelf is a passive daylighting system that functions as a horizontal overhang. The upper surface is made of reflective materials, which simultaneously provide shading, increase the penetration depth of light, reduce the use of artificial lighting systems, and consequently lower energy consumption. Light shelves reflect direct sunlight onto the ceiling and subsequently diffuse it into the room, minimizing glare near the windows [7] (Figure 1).

Table 1. Classification of studies in field of light shelves.

	Testing Method	Space Utilization	Type of Light Shelf (Static/ Dynamic)	Orientation	Field of Investigation (Daylight Quality–Energy Consumption–Thermal Comfort)	Approaches
[8]	IESVE	Office	Static	South–North–East–West	Daylight	Integration with horizontal light tubes
[9]	DIVA	-	Static	South	Daylight	Use of various ceiling forms
[10]	DIVA	Educational	Static	South–North–East–West	Daylight	Evaluating the impact of light shelf geometry on daylight quality and visual comfort
[11]	DIVA	Healthcare	Static	East–West	Daylight	Optimizing light shelf proportions for improved daylight quality
[12]	DIVA	Educational	Static	South	Daylight	Investigating the effect of light shelves on space lighting quality
[13]	Honeybee and Ladybug	Office	Static	South	Daylight, Energy Consumption	Sensitivity analysis and optimization to determine suitable light shelf parameters
[14]	Field Measurement	Educational	Static	South	Daylight	Proposing translucent and curved internal light shelves
[15]	Honeybee and Ladybug/ Open Studio	Educational	Static	South–North	Daylight, Thermal Comfort	Optimizing light shelf proportions for improved daylight and thermal comfort
[16]	Honeybee	Residential	Static	Northwest–Northeast–Southeast–Southwest	Daylight, Thermal Comfort	Use of a series of light shelves
[17]	Honeybee and Ladybug–Field Measurement	Office	Static	South	Daylight	Optimizing light shelf proportions to improve daylight quality
[18]	Ecotect	Educational	Dynamic	South	Daylight	Integration with louvers
[19]	Ecotect–Field Measurement	Educational	Static	South	Daylight	Integration with louvers
[20]	Radiance/ Ecotect	Office	Static	South	Daylight	Investigating latitude impact on light shelf proportions
[21]	Radiance	-	Static	South	Daylight	Use of curved ceilings
[22]	Radiance–Field Measurement	Office	Dynamic	South–North–East–West	Daylight	Use of dynamic light shelves for tropical climates
[23]	Radiance–Field Measurement	-	Static	South	Daylight	Use of various ceiling forms
[24]	Radiance–Field Measurement	Office	Dynamic	South–East–West	Daylight, Energy Consumption	Integration with a set of mirrors
[25]	Relux	Educational	Static	Northeast–Southwest–Northwest	Daylight	Integration with louvers
[26]	TracePro7.0	Residential	Static	South	Daylight	Proposing unique windows above light shelves
[27]	Design Builder	Educational	Static	East–West	Daylight, Energy Consumption, Thermal Comfort	Evaluating light shelf performance
[28]	DIALux 4.13 program	Educational	Static	South–North–East–West	Daylight	Use of a series of light shelves
[29]	Energy Plus/Comfen	Office	Dynamic	South	Daylight	Integration with horizontal and vertical shading devices
[30]	DeLuminae	Office	Static	South–North–East–West	Daylight	Integration with translucent ceilings aligned with light shelves
[31]	Lightscape	Office	Static	South	Daylight, Energy Consumption	Integration with louvers
[32]	Field Measurement	-	Static	South	Daylight, Energy Consumption	Integration with daylight diffusing sheets
[33]	Field Measurement	-	Static	South	Daylight, Energy Consumption	Integration with solar panels
[34]	DIVA	Office	Static	South	Daylight, Energy Consumption	Integration with solar panels
[35]	Field measurement	-	Static	South	Daylight quality Energy consumption	Integration with solar panels
[36]	Field measurement	-	Dynamic	South	Daylight quality Energy consumption	Integration with solar panels
[37]	Field measurement	-	Dynamic	South	Daylight quality Energy consumption	Integration with solar panels
[38]	Honeybee and Ladybug	Educational	Static	South	Daylight quality Energy consumption Thermal comfort	Integration with solar panels

classifies the studies conducted in this field based on the type of light shelf—whether static or dynamic—and the orientation of the window. As demonstrated in the reviewed literature, light shelf performance is typically evaluated using two main approaches: experimental methods and computer simulations. Experimental studies are carried out using scaled or full-scale models tested under real or artificial sky conditions. However, with the rapid advancement of simulation technologies in recent years, software-based methods have become more prevalent. Among the simulation tools, the Radiance engine and the Honeybee-Ladybug plugin are the most commonly used. Other tools, including DIVA, Ecotect, Climate Studio, OpenStudio, IESVE, COMFEN, Lightscape, DesignBuilder, Relux, and TracePro7, have also been utilized for performance evaluation [2]. Most studies have focused on spaces with educational and office applications due to the higher potential for utilizing these systems in spaces where usage time aligns with the presence of the sun in the sky. Moreover, this table categorizes the studies according to the performance metrics considered, namely daylight quality, energy consumption, and thermal comfort.

Examination of the metrics listed in the table reveals that most studies have focused on optimizing light shelf specifications primarily to enhance daylight quality [17], while only a limited number have simultaneously evaluated energy consumption and thermal comfort. However, addressing energy performance is essential in this field. One study, for instance, reported that in a school equipped with transparent curved light shelves, post-occupancy assessments showed a 40% reduction in glare and a 10% decrease in cooling load compared to the original condition [14].

Based on research conducted in this field, the most common indicators used to evaluate daylight conditions were sDA, UDI, and sGA [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. sDA is defined as the percentage of the regularly occupied area of a space that receives a minimum daylight illuminance (typically 300 lux) for at least 50% of the annual occupied hours. This metric helps evaluate whether sufficient daylight is provided without relying on electric lighting [39,40]. UDI quantifies the percentage of a space that receives daylight within a “useful” range of illuminance. Typically, this range is defined to exclude values that are too low (below 300 lux, where light is insufficient for most tasks) or excessively high (above 2000 lux, which may cause glare or discomfort). This metric ensures that the daylight available is both functional and comfortable for occupants [40]. According to the Lighting and Visual Comfort Guidelines published by the New Zealand Ministry of Education (2023), an appropriate daylighting target for educational spaces is to achieve a Useful Daylight Illuminance (UDI) within the range of 300–2000 lux for at least 60% of school hours across a minimum of 50% of the floor area [41]. sGA measures the proportion of an occupied space that remains free from glare issues over the course of a year. In practice, it is used to assess the areas where glare is unlikely to cause visual discomfort, complementing the sDA metric. A study published in Buildings (2024) indicates that achieving optimal visual comfort in educational spaces requires maintaining a Spatial Glare Autonomy (sGA) value close to 1, which implies that all regularly occupied areas remain largely free from significant glare throughout school hours [42].

In the limited number of studies that have examined thermal comfort and energy consumption alongside daylight parameters, two key indicators—Energy Use Intensity (EUI) and Thermal Comfort Percentage (TCP)—have commonly been used. TCP represents the percentage of time during which the indoor environment meets established thermal comfort conditions as defined by standards such as ASHRAE Standard 55 [38]. Also, EUI measures the energy consumption of a building normalized by its floor area, expressed in kWh/m²·year. This table also reviews the window orientations analyzed in the studies, with south-facing windows being predominantly chosen, as they provide the highest efficiency for light shelf systems due to direct sunlight exposure [7]. The fourth column examines the proposed systems in terms of whether they are static or dynamic. Most of the reviewed systems are static and applied uniformly throughout the year, while fewer studies recommended dynamic systems that adapt to seasonal changes. However, research shows that dynamic systems can achieve up to 50% more energy savings compared to static systems [43,44,45,46].

The last column of the table presents the approaches of the studies. Based on the reviewed literature, three key parameters—geometry, depth, and reflectance of the light shelf—were identified as the most influential factors affecting the system’s performance.

In the conducted research, three different light shelf forms—flat, angled, and curved—are introduced and evaluated (Figure 2).

One study found that a curved light shelf with a 60-degree arc angle and a 20-degree installation angle improved illuminance uniformity and lowered lighting energy consumption compared to flat shelves [35]. Similarly, another study demonstrated that curved forms outperform flat and angled shelves in daylight penetration and visual comfort [47]. However, a common limitation in these studies is the consideration of a fixed light shelf form for year-round application, without separate evaluations for different seasons.

In previous studies, the effect of light shelf depth on daylight performance has also been investigated. A study by Moazzeni and Ghiabaklou [10] optimized external shelf depth under various sky conditions and orientations, concluding that a depth of 60 cm improved daylight distribution and glare reduction in a classroom. In another study, Bahdad and Farzil [17] evaluated different depths of external light shelves across all four seasons. They found that optimal depth varies seasonally, recommending greater depths in winter and autumn when the sun is lower in the sky and shallower depths in spring and summer.

In addition to geometry and depth, the reflectance coefficient of the light shelf surface plays a crucial role in enhancing daylight performance. A higher reflectance value leads to better reflection and distribution of daylight into interior spaces, improving illuminance uniformity and reducing glare. Many studies recommend using materials with reflectance values above 70%, such as matte white paint or reflective metal coatings, to maximize the efficiency of light shelves [7].

While each of the previous studies has contributed valuable insights into the role of geometry, depth, or surface reflectance of light shelves, the scope of these investigations has been limited to improving one or two parameters in isolation. To the best of the authors’ knowledge, no prior research has conducted a comprehensive, simultaneous assessment of all three parameters with the aim of identifying an integrated and seasonally responsive light shelf design.

Also, many studies have been conducted on the integration of light shelves and solar panels. In several cases, photovoltaic cells have been installed directly on top of the light shelf [33,34]. However, in these cases, the optimal angle for installing solar panels does not align with the ideal angle of a light shelf for efficiently redirecting daylight into the room. Moreover, placing photovoltaic panels on the light shelf reduces its reflectivity, impairing its primary function of light redirection and turning it into a mere shading device. As a result, this configuration compromises the performance of both systems.

In another attempt to address this issue, solar cells were installed beneath a curved light shelf; however, this setup also proved inefficient, as the photovoltaic cells were not oriented at optimal angles [35]. Furthermore, various studies have shown that solar panels perform poorly during the summer months due to high temperatures. Therefore, it is recommended that their integration with light shelves be avoided during this season [34,35].

Consequently, two key considerations must be taken into account when integrating light shelves with solar panels:

• Photovoltaic panels should not be mounted directly on the light shelf but should instead be installed at their optimal tilt angles.
• Integration of solar panels with light shelves is more appropriate during the winter season.

Theoretical Foundations and Research Objectives

A review of the existing literature highlights significant limitations in current light shelf systems used in educational buildings. While light shelves have been widely employed to enhance daylight distribution, they are insufficient in fully preventing glare, particularly during winter months when the solar altitude is low. Studies typically mitigate glare by combining light shelves with fixed shading devices such as louvers or diffusing sheets applied uniformly throughout the year [19]. A glare analysis was conducted using the Climate Studio plugin in a typical classroom, employing a simple flat light shelf with an exterior depth of 60 cm, which is recognized as an appropriate dimension for light shelves in Tehran [10]. As shown in Figure 3, glare is still present in both autumn and winter despite using this depth. In autumn, the glare is relatively mild and can be addressed by slightly increasing the depth of the light shelf. However, in winter, the sun’s lower angle results in severe glare that cannot be adequately mitigated by increasing shelf depth alone. Therefore, the need for an additional shading element arises predominantly during the winter months, when the sun’s lower altitude increases the risk of direct glare, and in autumn, increasing the depth of the light shelf is sufficient to mitigate glare without requiring extra shading, which could obstruct the view.

At the same time, previous studies on solar panels indicate that their use is more suitable in winter, as their efficiency in electricity generation improves during this season [34,35]. Therefore, considering that solar panels can provide the electrical energy needed to operate a dynamic light shelf system, and that the period requiring additional shading coincides with the optimal integration time for solar panels, one of the objectives of this paper is to determine the optimal method for integrating photovoltaic panels as a shading system with the light shelf, ensuring effective performance of both systems.

Nevertheless, a major research gap remains. Most studies focus on evaluating only one or two parameters of light shelf design—typically depth or geometry—while neglecting their interaction with surface reflectance. The combined influence of geometry, depth, and reflectance across different seasons has not been thoroughly explored, despite its potential to enhance both visual comfort and energy performance.

Based on these observations, this study is guided by the hypothesis that a seasonally adaptive light shelf system, which dynamically adjusts its geometry, depth, and surface reflectance and integrates PV panels as temporary shading during winter, can deliver superior results compared to traditional fixed systems (Figure 4).

Accordingly, the key research objectives are as follows:

• How can photovoltaic panels be employed to simultaneously prevent glare during winter and generate electricity at their maximum potential?
• What is the most suitable combination of geometry, depth, and surface reflectance for the light shelf to achieve its highest performance across different seasons?

2. Materials and Methods

2.1. Research Process

Figure 5 presents the overall research workflow developed in this study. The process began with the selection of a representative classroom located in Tehran, Iran (35°N latitude, 51°E longitude), a city that experiences over 200 days of sunshine annually. A preliminary climate analysis was conducted using long-term meteorological data in combination with the Ladybug and ClimateStudio plugins. Following this, a detailed three-dimensional model of the classroom was constructed using Rhinoceros 7 and Grasshopper. This model was employed to assess daylight availability, energy consumption, and thermal comfort across all four seasons. The light shelf was placed at an elevation of 2.10 m, a height identified in prior research as optimal for minimizing glare for seated occupants [7,10]. The simulation phase was organized into two main stages: (1) evaluating the integration of photovoltaic panels as a winter-specific shading strategy, and (2) optimizing the seasonal configuration of the light shelf, including its geometry, depth, and surface reflectance.

• Integration with solar panels:

During the winter season, when the solar altitude is low and the potential for glare is significantly increased, photovoltaic (PV) panels are integrated into the design as a seasonal shading solution. This approach aims to provide effective glare mitigation while simultaneously enabling on-site renewable energy generation. Four design scenarios were evaluated, consisting of one to four PV panels with cumulative depths ranging from 15 cm to 60 cm. Using ClimateStudio, each configuration was assessed in terms of visual comfort and electricity production. The optimal tilt angle for the panels was also determined to maximize annual energy yield under Tehran’s winter solar conditions.

2.

Finding a suitable combination of geometry, depth, and reflectance for each season:

Previous research identified a fixed external light shelf with a 60 cm depth as suitable for classrooms in Tehran [10]. In the present study, this depth was implemented using four modular segments of 15 cm each. However, simulations showed that a 60 cm depth is insufficient to effectively control glare during winter, spring, and autumn, while a shallower shelf may be more effective in summer. Therefore, various shelf depths (75 cm, 60 cm, and 45 cm) were analyzed to identify the optimal dimension for enhancing daylight performance while minimizing glare in each season. Additionally, five distinct forms of light shelf—horizontal, horizontal with fixed angle, horizontal with variable angle, sloped, and curved—were examined. For each type, a parametric range of angles and curvatures was tested to determine the most effective configuration for each season.

To select the optimal design alternative, a structured three-filter evaluation process was applied, incorporating both benchmarking and comparative analyses (Figure 6). In Filter 1 (benchmarking analysis), design options that met the required daylight performance criteria—specifically achieving at least 50% in sDA and 60% in UDI metrics—were identified based on the LEED daylighting credit guidelines [39,40] and the Lighting and Visual Comfort Standards issued by the Ministry of Education of New Zealand [41]. Next, in Filter 2 (comparative analysis), among the qualifying options, the alternatives with the lowest level of glare were prioritized, reflecting the primary objective of the study: to improve daylight quality in learning environments. Finally, Filter 3 was applied to further distinguish between alternatives with similar daylight and glare performance, selecting the one with lower energy consumption and higher thermal comfort. All design scenarios were simulated for spring, summer, autumn, and winter using Ladybug for thermal comfort analysis, Honeybee for daylight metrics (sDA, UDI, sGA), and ClimateStudio v2.0 for evaluating photovoltaic output and building energy demand (cooling/heating loads and EUI).

It should be noted that the Spatial Glare Autonomy (sGA) index, used to evaluate the potential for glare discomfort among occupants, was assessed at a height of 120 cm above the floor, corresponding to the seated eye level of students. In contrast, the daylight-related metrics including Spatial Daylight Autonomy (sDA), Useful Daylight Illuminance (UDI), and Annual Sunlight Exposure (ASE) were analyzed at a height of 75 cm, representing typical desk level.

Sensor points were spaced at 50 cm intervals and positioned 50 cm away from all walls to ensure uniform coverage across the classroom. To enhance the accuracy of daylight simulations in Radiance, the number of ambient bounces (i.e., diffuse inter-reflections between surfaces) was set to six, as recommended in previous validated studies [48] (

Table 2. Values of parameters applied to the Radiance daylight simulator.

Value	Effective Parameters in Simulation
6	Number of Diffuse Reflections Between Surfaces (ab)
2500	Number of Rays Emitted from Surfaces in Calculations (ad)

).

The occupancy schedule and ventilation requirements for spaces were defined in accordance with Appendix 5 of Chapter 19 of the National Building Regulations [35]. According to this appendix, the main operational hours for spaces are set from 7:00 AM to 2:00 PM, with Thursdays and Fridays being holidays. The activity rate for classroom users is defined as 120 watts per person, remaining constant throughout the year.

Additionally, the occupancy of the space is considered to be 25 people. Furthermore, based on Chapter 14 of the National Building Regulations, the minimum required outdoor air intake for classrooms is defined as 1.7 L per second per person, with the corresponding schedule aligning with building operational hours [49]. The suitable temperature settings for schools, as specified in Appendix 5 of Chapter 19, are defined as 20 °C for heating systems and 28 °C for cooling systems [50]. The thermal resistance values of the building components are as follows: the external wall has an R-value of 0.892 m²·K/W, the external roof has an R-value of 1.82 m²·K/W, and the internal floor has an R-value of 0.509 m²·K/W. Detailed reflectance values and surface material specifications used in the Radiance simulation are also presented in

Table 3. Surface material properties.

Reflectance	Color	Type of Material	Surfaces
0.201	Light Gray	Ceramic	Floor
0.822	white	Plaster	Interior Ceiling
0.701	Transparent	Double-Glazed Glass with 70% Visible Light Transmission	Window
0.812	white	Plaster	Wall
0.419	Light Brown	wooden	Door
0.077	red	Fabric	Curtain
0.87	white	Semi-Mirror Surface	Light Shelf

.

2.2. Research Context

Since light shelves perform significantly better under sunny skies and are less efficient under completely overcast skies [2,51], a school in Tehran with a latitude of 35° N and longitude of 51° E, featuring over 200 sunny days annually, was selected as the research context. Analysis of cloud coverage in Tehran indicates that fully overcast skies are experienced only 18% of the time throughout the year (Figure 7). Therefore, given the ample solar radiation, employing light shelves alongside solar panels in Tehran can significantly improve daylight quality, supply energy, and reduce energy consumption.

One of the classrooms in this school, with a length of 8 m, width of 7 m, and height of 3.1 m, along with two windows measuring 3.1 × 1.95 square meters on the southern side of the classroom, was selected as the primary research context (Figure 8).

2.3. Validation

To validate the daylight simulation results for a classroom on February 28th at 12:00 PM under overcast sky conditions, point-based measurements of horizontal illuminance were conducted at 12 sensor points across the floor plane at a height of 75 cm using a calibrated DT-856A lux meter (Figure 9). Following the field measurements, a 3D daylight model of the classroom was developed using Rhinoceros 7.

Table 4. Comparison of measured and simulated illuminance values at sensor points.

Sensor	Measured (lux)	Simulated (lux)
1	343	374
2	403	439
3	379	413
4	355	387
5	572	623
6	646	704
7	641	699
8	584	637
9	1241	1353
10	1215	1324
11	1209	1318
12	1385	1510

presents a comparison between the measured and simulated illuminance values at each sensor point. The simulation results yielded a Normalized Mean Bias Error (NMBE) of exactly +9.00%, indicating that the simulated values are slightly higher than the measured data but remain within acceptable limits. According to ANSI/ASHRAE Standard 140 [52], a model is considered calibrated if the NMBE is within ±10%, and this result satisfies that validation criterion. Furthermore, the Coefficient of Variation of the Root Mean Square Error (CVRMSE) was calculated to be 10.10%, confirming a small variation between simulated and measured values. These results support the reliability and accuracy of the daylight simulation model in representing actual indoor lighting conditions [53].

3. Results

The results section is structured based on the methodology described earlier and consists of three parts:

• Assessment of the existing classroom conditions;
• The appropriate integration of photovoltaic panels with the light shelf;
• The proposed suitable geometry, depth and reflectance of the light shelf in each season.

3.1. Assessment of Current Conditions

Simulations in a base classroom (without considering light shelves) revealed that during summer, thermal comfort issues arise due to increased room temperatures. In winter, glare becomes a significant problem, emphasizing the need for appropriate shading elements beneath the light shelves. The results of the simulations conducted, along with the values of the UDI, TCP, and EUI indices, are presented in Figure 10.

Based on varying seasonal conditions, light shelves with different forms are required throughout the year. To achieve this, the light shelf should be divided into smaller segments so that each segment can adopt an appropriate angle and depth for each season. Consequently, light shelves with depths of 45 cm, 60 cm, and 75 cm, in flat, angled, and curved geometries, were evaluated for their performance in each season.

3.2. The Appropriate Integration of Photovoltaic Panels with the Light Shelf

Using simulations conducted in the Climate Studio plugin, the optimal installation angle for solar panels in winter in Tehran was determined to be 60 degrees. To assess the optimal combination of light shelves with solar panels, four scenarios were evaluated (

Table 5. Types of integration.

Investigation of Different Modes of Integrating Solar Cells with a Light Shelf
Uniformity = 0.41	UDI = 76/9%	SDA = 95.7%	Depth of 60 cm (1 solar panel)
Uniformity = 0.42	UDI = 78.4%	SDA = 98%	Depth of 30 cm (2 solar panels)
Uniformity = 0.38	UDI = 79.2%	SDA = 98%	Depth of 20 cm (3 solar panels)
Uniformity = 0.4	UDI = 79.3%	SDA = 98.9%	Depth of 15 cm (4 solar panels)

).

• Single solar panel with a depth of 60 cm.
• Two solar panels, each with a depth of 30 cm.
• Three solar panels, each with a depth of 20 cm.
• Four solar panels, each with a depth of 15 cm.

The simulations demonstrate that employing four solar panels configured as louvers with a depth of 15 cm, positioned at a 60-degree angle during the winter season and located 34 cm below the light shelf, offers superior performance compared to other scenarios (Figure 11). This configuration effectively prevents glare issues while ensuring optimal efficiency. These panels, when placed at the ideal angle, not only achieve high performance but also generate energy to partially meet the classroom’s yearly energy consumption. The efficiency of each panel was assumed to be 15%, based on typical commercial PV modules. Using the Climate Studio plugin, the total annual energy production from these panels was calculated to be approximately 428.2 kWh/year, confirming their viability as a supplemental power source for operating the dynamic components of the light shelf system.

3.3. Proposed Suitable Geometry, Depth and Reflectance of Light Shelf in Each Season

As observed in the previous section, during winter, due to the low angle of solar radiation, a light shelf alone cannot effectively control glare. Therefore, in this part, five different forms of light shelves—horizontal, horizontal with fixed angle, horizontal with variable angle, sloped, and curved—were evaluated in combination with solar cells. The simulation results, presented in

Table 6. Analysis of the optimal form of light shelves in winter.

Daylight		Energy Consumption			ThermalComfort	Alternatives		4 Segments (Depth 60 cm)
UDI	sGA	Cooling	Heating	EUI	TCP
48.86%	0.50	33.53	3.086	68.43	35.38%		Existing classroom condition	0	Without Solar panels
52.38%	0.57	21.486	5.104	58.40	46.43%		Horizontal Light shelf	0
67.91%	0.70	14.72	13.41	59.95	75.82%		Horizontal Light shelf	1	With Solar panels
64.83%	0.650	15.01	12.40	59.24	73.6%		Horizontal Light shelf with fixed angle elements	2
63.86%	0.653	14.84	12.23	58.88	72.54%		Horizontal Light shelf with variable angle elements	3
64.23%	0.646	14.66	12.40	58.88	72.33%		Lightshelf with −10 angle	4
63.16%	0.641	14.18	12.16	58.16	72.44%		Curved Light shelf	5

, indicate that the flat light shelf performs better than the other configurations across all evaluated metrics. In this configuration, in addition to reducing energy consumption, glare is also minimized, resulting in the highest values for the UDI index and thermal comfort.

After determining the optimal form for the winter, three different light shelf depths—45 cm, 60 cm, and 75 cm—were evaluated. For each case, the installation height of the solar panels varied to ensure that they remained unshaded. As shown in

Table 7. Analysis of the optimal form of solar panels in summer.

Daylight		Energy Consumption			ThermalComfort	Alternatives		Analysis of the Depth of the Light Shelf
UDI	sGA	Cooling	Heating	EUI	TCP
66.10%	0.68	17.75	11.99	61.55	74.02%		3 segments with a depth of 45 cm	1	With Solar panels
67.91%	0.70	14.72	13.41	59.95	75.82%		4 segments with a depth of 60 cm	2
63.86%	0.653	14.84	12.23	58.88	72.54%		5 segments with a depth of 75 cm	3

, the simulation results indicate that a flat light shelf with a depth of 60 cm, combined with solar panels installed 34 cm below the shelf, delivers the best overall performance.

In summer, the issue of glare is absent, but the primary challenge is achieving thermal comfort. Simulations have determined that a light shelf depth of 45 cm is optimal for this season, as deeper shelves are unnecessary for glare mitigation. Additionally, simulations reveal that angled or curved light shelves outperform flat ones during summer, as they can direct sunlight deeper into the space, enhancing comfort conditions. To further improve comfort, simulations were conducted using reflectance coefficients of 50% and 70%, showing that light shelves with a 50% reflectance coefficient provided better performance during this season (Figure 12).

After determining the general form, depth, and reflectance coefficient for this season, it is necessary to identify the precise shape and placement angle of the light shelf. To evaluate the optimal curved form, curves with angles of 0°, 20°, 40°, 60°, 80°, and 100° are selected. Each of these curved surfaces can be oriented at an angle of 0°, 10°, 20°, 30°, 40°, or 50° relative to the horizon. This results in 36 possible configurations for the curved light shelf, which need to be thoroughly analyzed (Figure 13).

Due to the large number of possible configurations, the Design Explorer tool was used to explore the best option. The results showed that the optimal light shelf form for this season is a curved shelf with an angle of 80 degrees and a placement angle of 20 degrees (Figure 14).

Considering the proposed reflectance coefficients for summer, one side of the reflective panels has a reflectance coefficient of 80%, while the other side has a reflectance coefficient of 50%. For autumn and spring, both reflectance coefficients were simulated to identify the optimal configuration. The simulations revealed that, in autumn, a horizontal light shelf with a depth of 75 cm and a reflectance coefficient of 50% provides superior performance in terms of daylight distribution, thermal comfort, and energy efficiency (Figure 15).

In spring, similarly to autumn, simulations were conducted using both reflectance coefficients of 80% and 50%. After determining the general form, depth, and reflectance coefficient suitable for this season, it became necessary to establish the precise curvature and placement angle of the light shelf. To evaluate the optimal curved form, curves with angles of 0°, 20°, 40°, 60°, 80°, and 100° were selected. Additionally, each of these surfaces could be oriented at angles of 0°, 10°, 20°, 30°, 40°, or 50° relative to the horizon. This approach resulted in 36 possible configurations for the curved light shelf, all of which require thorough evaluation (Figure 16).

In this season, the optimal configuration for the light shelf is a curved form with an angle of 100 degrees and a placement angle of 20 degrees. This setup was selected based on simulations evaluating its performance in daylight distribution, thermal comfort, and energy efficiency (Figure 17).

Thus, the appropriate form and depth of the light shelf for each season were determined and are shown in Figure 18.

To adjust the depth of the proposed light shelf across different seasons, it is necessary for the segments of the light shelf to fold under one another, creating reduced depth as required. Moreover, since light shelves with different reflectance coefficients are needed in various seasons, each segment of the light shelf should function as a roll, providing either 50% or 80% reflectance. The detailed implementation of the proposed system is shown in the accompanying image (Figure 19).

With the implementation of the proposed system, the classroom conditions in terms of daylight and thermal comfort were assessed. Results indicate significant improvement in all aspects across every season. Moreover, the proposed system has successfully reduced annual energy consumption by approximately 10% (

Table 8. Analysis of suitable light shelf types for each season.

Daylight		Energy Consumption			ThermalComfort	The Type of Light Shelf Suitable for Each Season	Season
UDI	sGA	Cooling	Heating	EUI	TCP
83.93%	0.872	20.48	6.71	59.00	45.76%	The current situation	Spring
96.87%	0.965	15.61	8.84	56.27	55.96%	A curved light shelf with 100 degree angle and 20 degree placement with depth of 75 cm and a reflectance coefficient of 50%
84.20%	0.85	40.30	0.83	73.95	11.07%	The current situation	Summer
95.94%	0.947	20.77	1.19	60.66	43.89%	A curved light shelf with 80 degree angle and 20 degree placement with depth of 45 cm and a reflectance coefficient of 50%
56.41%	0.564	18.64	8.49	58.94	48.69%	The current situation	Autumn
71.33%	0.6625	12.82	12.23	56.86	57.095%	A flat depth of 75 cm with a reflectance coefficient of 50%
48.86%	0.50	33.53	3.086	68.43	35.38%	The current situation	Winter
67.91%	0.70	14.72	13.41	60.95	75.82%	A flat depth of 60 cm integrated with solar panels

).

4. Discussion

The light shelf system, due to its capacity to redirect daylight deeper into interior spaces and improve the uniformity of illumination, has been widely recognized as a viable passive strategy for enhancing visual comfort in classrooms. However, its application alone is often insufficient to fully mitigate issues such as glare, particularly during low-solar-angle periods. As a result, the integration of supplementary shading elements becomes necessary to achieve optimal performance.

In this study, the proposed system demonstrates significant improvements over previous light shelf designs through two key innovations. First, it introduces a seasonal integration of photovoltaic (PV) panels as winter-specific glare-control elements that simultaneously generate renewable energy. Second, it presents an adaptive configuration of the light shelf—varying in geometry, depth, and surface reflectance—tailored to seasonal climatic conditions. Each of these design strategies is critically examined and compared with existing research to underscore the added value and holistic effectiveness of the proposed approach.

4.1. Integrating Photovoltaic Panels with Light Shelf as Shading System During Winter

Previous studies have commonly proposed fixed, year-round shading systems in combination with light shelves to mitigate glare in educational or office spaces. For instance, Meresi [19] and Öner and Kazanasmaz [25] evaluated light shelf configurations with static external blinds or reflective louvers that remained in place throughout the year, effectively blocking glare but also permanently obstructing the outdoor view. Similarly, Moon et al. [31] and Lee et al. [32] developed and tested systems with fixed shading elements or diffusion sheets that provided consistent glare control yet limited visual connection to the exterior across all seasons.

In contrast, the simulation results in this study indicate that such fixed approaches may be unnecessarily restrictive. Our findings demonstrate that the need for an additional shading element arises predominantly during the winter months, when the sun’s lower altitude increases the risk of direct glare. In spring and autumn, however, increasing the depth of the light shelf alone is sufficient to mitigate glare without requiring extra shading. Based on this seasonal performance analysis, we propose a dynamic solution that integrates photovoltaic (PV) panels as a winter-specific shading element. This system provides effective glare control when needed, while preserving outdoor visibility during the majority of the year.

Given the overlap between the occurrence of glare and the optimal operating period for PV panels in winter, this study proposes using photovoltaic (PV) panels as seasonal glare-control devices. The integration strategy was evaluated through simulation and performance analysis. The final recommendation involves four PV segments, each 15 cm in depth, tilted at 64 degrees, and installed 34 cm below the light shelf. This configuration proved effective in mitigating winter glare while maintaining a clear outdoor view during the rest of the year. Additionally, the generated electricity can be used to power the dynamic movement of the system, enhancing its self-sufficiency.

Several recent studies have also investigated combining PV panels with light shelf systems to integrate daylighting with renewable energy generation. In most cases, as demonstrated by Lee et al. [33] and Mesloub and Ghosh [34], PV modules were mounted directly on the upper surface of the light shelf. However, this configuration results in suboptimal energy performance due to improper tilt angles for solar collection, especially during non-peak periods. Moreover, such placement significantly reduces the reflectance of the shelf surface, undermining its primary daylighting function. A more advanced approach was explored by Lee and Lee [35], who attached flexible PV panels beneath a curved shelf to improve light redirection, yet their design still suffered from inefficient solar performance due to low tilt angles.

In contrast, the PV-integrated system proposed in this study is both seasonally responsive and geometrically optimized. By activating the PV shading elements only in winter, when panels operate more efficiently due to lower ambient temperatures [34], the system avoids year-round compromises in daylight quality and view. This dual-function solution ensures effective glare control, maximized solar gain during the most suitable season, and minimal interference with visual comfort and daylight performance during spring, summer, and autumn. Consequently, the proposed configuration addresses the limitations of previous PV–light shelf integrations and offers a more balanced and high-performance alternative for sustainable daylighting design.

These findings challenge the assumption made in previous studies that year-round fixed shading is necessary in daylight-responsive classrooms. Instead, they support a more flexible, climate-adapted approach that simultaneously improves visual and energy performance.

4.2. Proposed Suitable Geometry, Depth, and Reflectance of Light Shelf in Each Season

Most previous studies have focused on optimizing only one or two of these parameters without considering their combined effects. In contrast, this study offers a more comprehensive approach by simultaneously evaluating all these three parameters that influence the performance of light shelves. This integrated evaluation enables a better understanding of how their interaction affects visual comfort and energy performance across different seasons.

Using simulations conducted with the Honeybee–Ladybug plugin, it was found that a curved (parabolic) form provided superior daylight distribution in spring and summer, while a flat form performed more effectively in autumn and winter. Shelf depth also showed seasonal sensitivity: 45 cm in summer to reduce overheating, 75 cm in spring and autumn for glare control, and 60 cm in winter when integrated with photovoltaic panels.

Regarding surface reflectance, the results showed that lower reflectance (50%) in summer minimized cooling demands, while higher reflectance (80%) in seasons with lower solar altitude increased indoor daylight availability. Unlike earlier studies that often prioritized only daylight performance, this research simultaneously addressed visual comfort, energy use, and thermal impact through coordinated adjustments of all three parameters.

For instance, Lee and Lee [35] investigated a curved shelf form with a 60-degree arc angle and 20-degree installation angle, finding improvements in illuminance uniformity and a 15% reduction in lighting energy consumption, but without varying design across seasons. Similarly, Warrier and Raphael [54] demonstrated enhanced glare reduction with curved forms, but they applied a fixed design year-round and did not consider reflectance or depth variations.

This holistic approach demonstrates the added value of evaluating geometry, depth, and reflectance in an integrated manner rather than in isolation. It provides a more robust basis for designing effective light shelf systems tailored to specific climatic and spatial conditions, particularly in educational spaces such as classrooms.

The proposed system thus achieves better overall performance across all seasons compared to prior studies. This system not only improves daylight quality and reduces glare but also enhances thermal comfort and lowers energy use in classrooms. This allows students to benefit from the many advantages of natural daylight, including better visual comfort and improved learning performance.

In this research, the simulations were conducted based solely on the climatic conditions of Tehran; performance in other geographic and climatic contexts may vary. Also, this research did not include a cost–benefit analysis or evaluate the use of locally available materials. Future research is recommended to explore these aspects and assess the applicability of the proposed system in other climates.

5. Conclusions

This study proposed and evaluated a seasonally adaptive dynamic light shelf system for classrooms in Tehran, aiming to simultaneously improve daylight quality, thermal comfort, and energy efficiency. Through parametric simulations using Honeybee-Ladybug and Climate Studio, the performance of 36 different configurations was assessed across all four seasons.

The proposed system demonstrated several key advantages over previous fixed or semi-dynamic designs. It incorporates a dynamic seasonal strategy in two main aspects: 1. integrating photovoltaic panels with optimal tilt angles to enhance solar energy generation and preventing glare, and 2. adjusting light shelf geometry, depth, and reflectance seasonally to respond to solar altitude changes and comfort requirements. Compared to prior research, this holistic and responsive approach led to a 21% increase in Useful Daylight Illuminance (UDI), a 65% improvement in Thermal Comfort Percentage (TCP), and a 10% reduction in annual Energy Use Intensity (EUI).

By integrating daylighting, shading, and renewable energy generation within a climate-specific and seasonally responsive design framework, the proposed system offers a comprehensive and high-performance solution for sustainable classroom environments in Tehran. This adaptive approach can serve as a practical model for other educational buildings and similar indoor spaces in climates with significant seasonal variations.

Future research should include user-centered evaluations, cost–benefit analyses, and material feasibility studies to assess the system’s real-world applicability. Moreover, testing its adaptability in other climates and building types (such as offices or libraries) would help generalize its potential for broader sustainable architectural practice.