Optimisation of light environment in architectural space based on multi strategy collaboration – A case study of a manual drawing classroom

Abstract

From the perspective of dynamic lighting throughout the year, reflector and louvre are proposed to add to the south-facing window. The optimal parameter is 2.0 m height and 1.0 m width reflector and a louvre angle of 75°. However, when further analysing the indoor illumination and uniformity, the classroom still had high or low illumination during certain periods solely relying on natural lighting, indicating that a single strategy alone cannot meet the overall lighting environment comfort needs of the space. The study suggests that different lighting environments should be used in different seasons, periods and areas of the classroom. The proportion of natural light, combined light and artificial light environments should be 30%, 45% and 25%, respectively. At the same time, considering the transformation and optimisation of the lamps, the improvement measures for windows facing other directions in the classroom is recommended, the lamps be symmetrically distributed in the horizontal direction, with a hanging height of 1.9 m in the vertical direction, which is 0.4 m higher than the original. The lighting power is 34 W and 26 W, and corresponding optimisation strategies for the intelligent control system are proposed.

Keywords

Manual drawing classroom Multi strategy collaboration Dynamic lighting Natural lighting environment Combined lighting environment

Introduction

Due to the advancement of socioeconomic status and enhancement of material well-being, there is a growing demand for diverse spatial lighting environments. Classrooms serve as educational spaces that integrate material and spiritual aspects. The quality of the lighting environment directly impacts users’ visual experiences and significantly influences their learning efficiency as well as their physical and mental health. Recently, numerous construction and expansion projects have been undertaken at universities and colleges in China. However, it is common to find classrooms with curtains drawn open on sunny days, which results in wasteful utilisation of lighting resources and increased energy consumption. Therefore, optimising the quality of classroom lighting environments, improving building energy efficiency and reducing energy consumption for lighting have gradually emerged as topics of concern.

Regarding the enhancement of natural lighting conditions in classrooms, Michael and Heracleous¹ conducted a survey on typical educational buildings in Cyprus and identified instances of glare occurring in certain areas with high lighting contrast and excessive brightness, particularly in east-west facing classrooms. Wagdy and Fathy² employed Rhino for the Grasshopper software to simulate and calculate all possible combinations of five parameters, including window-to-wall ratio, number of shutters, shutter tilt angle, screen depth ratio and screen reflectivity, for southward-facing classrooms located in the desert region of Cairo, Egypt. Their objective was to determine the optimal scheme for achieving an ideal lighting environment. In addition, studies have simultaneously investigated the correlation between lighting conditions and shading methods. Kotbi³ determined the optimal configuration of perforated screen parameters by adjusting factors such as the perforation rate, depth ratio, size and tilt angle of perforated solar panel screens to achieve satisfactory indoor natural lighting while ensuring privacy for girls’ schools in Saudi Arabia. Sun⁴ examined the impact of various shading forms on the internal illumination levels and proposed an optimisation strategy. Zhang et al.⁵ evaluated the effectiveness of different types of high-performance glasses and external shading techniques. Lin et al.⁶ conducted comprehensive research on the design aspects of adjustable shading systems.

Regarding artificial lighting environments in classrooms, Ibanez et al.⁷ conducted on-site measurements and captured highly dynamic photos to analyse the comfort of lighting brightness in drawing classrooms. They concluded that optimising the position and utilising the internal surfaces, lamps and lanterns could effectively enhance the lighting distribution strategies. Nurrohman et al.⁸ employed the DIALux light simulation method to design a novel university lamp set that reduced energy consumption. Meresi⁹ used Radiance software to define the optimal characteristics such as lamp stand width, installation height, inclination angle and reflection index, to improve daylight performance in typical classrooms in Athens, Greece. Bi and Yang¹⁰ emphasised the importance of creating a conducive physical environment by maximising natural light utilisation and carefully selecting appropriate lamps to enhance architectural drawing environments. Regarding lighting technology advancements, Cao et al.¹¹ proposed integrating pipeline daylight lighting devices with optical fibre technology to maximise natural light usage.

In addition, there are certain practices for optimising and transforming the classroom light environment. The Sidwell Friends Middle School in the United States, designed and constructed by Kieran Architects, flexibly adopts various types of shading reflectors according to the local weather conditions, thereby effectively controlling the entry of natural light, preventing glare caused by a low light angle or excessive light entering the indoor environment and causing glare, and other adverse indoor light environment factors. The Ash Creek Middle School, designed and constructed by BOORA Architects, prevents excessive outdoor natural light and low-angle natural light from entering the indoor environment by adjusting the length and angle of the shading plate. In addition, the shading plate is installed indoors to reflect the natural light deeper indoors, thus improving the uniformity and aesthetic feeling of indoor lighting.¹²

The above studies provide important references and a basis for further research on this topic. However, most relevant studies^1–12 have focused on classrooms in primary and secondary schools and general classrooms in universities; no studies have specifically focused on classrooms of manual drawing. Since 2020, the research team has conducted a series of studies on the lighting environment of classrooms of manual drawing.^13–15 In this study, the light environment requirements of classrooms of manual drawing were found different from those of other types of classrooms, and the optimisation design methods were also different. The classroom of manual drawing is a space specifically designed for students majoring in drawing. Generally, there are specific classrooms in universities that satisfy students’ various needs such as learning, manual drawing, discussion and communication. The course is mostly taught in professional classrooms, and the mode is face-to-face communication of drawings between teachers and students, as well as group communication amongst students.^16–24 The activity area of teachers is not limited to the podium, and the activity area of students is not limited to seats. Therefore, in the classroom layout, the arrangement of desks and chairs is flexible and can be changed according to users’ needs to facilitate discussion. As shown in Figures 1 and 2, compared with the general classroom, the classroom of manual drawing has the characteristics of diversity, professionalism and openness, and is different in the mode of use, hardware facilities, learning tools and lighting fixtures. Based on these learning characteristics, it is necessary to analyse and discuss the light environment in combination with actual cases.

Therefore, based on previous research,¹³ this study explored the optimisation of lighting environments in classrooms. The purpose of this study was (1) to analyse the current situation of indoor light environments based on the actual case of an architectural classroom; (2) to determine the optimal parameter combination of the reflector and louvre components from the perspective of optimising natural lighting; and (3) to study the suitable form of light environment in different periods of the classroom, discuss the improvement measures of lamps under the combined light environment, and propose an intelligent regulation method for light environments. The research results provide an empirical reference for optimising the design of light environments in professional classrooms in Beijing.

Research method

Case study

The case study involved a classroom of manual drawing at a university in Beijing. The classroom is located on the fifth floor of the teaching building. Daylighting was mainly distributed on the north and south sides, with two on the middle of the east side. Side-window lighting is also used. The space was used by 50 students and four teachers. Figure 3 shows the classroom plan and section. The space size is 14.4 m × 7.6 m × 3.3 m. The size of the daylighting window on the north-south facade of the building is 2.04 m × 1.72 m, and the size of daylighting window in the east is 1.42 m × 1.74 m, 1.0 m away from the ground. Because the study desks were arranged in the south- and north-facing spaces, they were referred to as S and N areas, respectively. The indoor lighting fixtures in the classroom were LED lights, 1.47 m away from the working surface, with a power of 34 W and a colour temperature of 5000 K for each lamp.

The survey found that the students in this classroom spend a long time in the classroom, approximately 6 to 9 h a day. The learning behaviour mainly includes hand drawing, making models, computer graphics, communication and discussion, and drawing evaluation. The survey found that the indoor light environment quality of the classroom was poor mainly because (1) the classroom used less natural light during the daytime. Because of the strong direct indoor sunlight at some times, students use sunshades, resulting in the classroom being in an artificial lighting environment in the daytime, causing significant wastage of energy, as shown in Figure 4(a). (2) The indoor illumination is very uneven, affecting visual comfort, as shown in Figure 4(b). (3) The light rays from the lamps on the working surface were too bright to affect students’ drawing work. Some students directly applied paper shading to the lanterns, but the illumination was too low, as shown in Figure 4(c). Figure 5(a) shows the questionnaire results. In the absence of sunshades in the classroom, 51.2% of students reported occasional exposure to harsh light, whereas 20.8% reported frequent exposure to harsh light. This indicates that most students were affected by glare during class, and it is reflected that during the period, 10 a.m. to 12 noon, direct sunlight from the south-facing window position produced severe glare. Figure 5(b) and (c) show the simulated lighting conditions of the south-facing window during the noon period, with the average brightness of the south-facing window being five times that of the adjacent background wall. The indoor light environmental quality of classrooms must be optimised and improved.

Evaluation index

In the current educational building design specifications in China, only the window-to-ground ratio, daylighting coefficient, daylighting uniformity and other evaluation indices have strong regulations on architectural design, which have very limited reference value for architectural design.²⁵ For example, although the window-to-ground ratio can guarantee the window area of the building to a certain extent, it cannot ensure the actual indoor daylighting quality, and has no guiding significance for the design of window openings; daylighting coefficient itself has certain controversies, and its test environment requirements are standard all-overcast environment. However, in real life, weather, sunshine, humidity and other factors vary with time, and sunlight conditions are also different depending on the geographical location of the building, which cannot be reflected by the daylighting coefficient. Therefore, the above static evaluation indices, as the basis for guiding the design of architectural light environments, have significant drawbacks.

With the development of computer technology and the emergence of all-weather light environment simulation software, several new dynamic lighting evaluation indices have emerged.^26–31 Therefore, based on illumination and illumination uniformity indices reflecting the basic quality of indoor light environments, this study conducts an in-depth comparative analysis of dynamic lighting indices, including daylight automation (DA), useful daylight illumination (UDI) and annual sunlight exposure (ASE).

(1) According to the Standard for Architectural Lighting Design,³² the minimum illumination for the classroom of manual drawing was 450 lx and the illumination uniformity was 0.7.

(2) DA refers to the percentage of time when the working surface illumination exceeds a certain target illumination value in the total working time under pure natural lighting during the working period of the year. The higher the value of DA_450lx, the greater the proportion of time exceeding 450 lx.

(3) The UDI is an important parameter for evaluating the quality of light environments. This refers to the percentage of time when the working surface illumination at a certain position in the room is in the effective lighting range during the working period of the year. Students in professional classrooms work on computers for a long time, and visual fatigue occurs under a long-term illumination environment of 1000 lx.³³ Therefore, the effective lighting range is 450–1000 lx. In this study, the average value of UDI_450lx-1000lx in professional classrooms was calculated. The larger the value, the greater the area in the effective lighting range.

(4) The ASE was used to measure the cumulative hours of direct sunlight illumination exceeding a certain limit during the working period of the year and to evaluate the visual discomfort caused by excessive direct sunlight. In this study, 1000 lx was considered the limit for direct sunlight illumination. ASE_1000lx,250h represents the ratio of the area with a cumulative time of more than 250 h of natural illumination higher than 1000 lx to the total area of the room during the working period. When ASE_{1000lx, 250} > 10%, the visual comfort was low, when ASE_{1000lx, 250} < 7%, the visual comfort was moderate, and when ASE_{1000lx, 250} < 3%, the visual comfort was good.³⁴

Software platform

The modelling platforms used in this study were Rhino and Grasshopper. Rhino offers a diverse range of modelling techniques, comprehensive data integration capabilities, and the ability to support numerous analysis plug-ins and programming extensions. Grasshopper, as a parametric design platform built on Rhino, enables the incorporation of performance simulation plug-ins and visualisation tools. Ladybug and Honeybee serve as simulation platforms: Ladybug facilitates the utilisation of local weather data, whereas Honeybee allows for the interactive design of two-dimensional and three-dimensional images. In a visual programming environment, model data can be captured to achieve real-time feedback during the design process. Honeybee incorporates Radiance and Daysim daylighting simulation engines that enable dynamic analysis of natural light conditions as well as artificial lighting environments to obtain relevant indicators.³⁵ For dynamic daylighting simulations, year-round climate data from Beijing area was employed, whereas for illumination simulations, climate data specifically from summer and winter solstices in Beijing area were utilised. Based on the actual dimensions of the investigated space, an appropriate model was established using the parameter flow illustrated in Figure 6.

Result analysis

Analysis of current indoor light environment

First, the natural lighting conditions during the daytime in the classroom of drawing were evaluated. The testing time was from 9 a.m. to 5 p.m. on a typical day in winter and summer, and the illumination was measured at the measurement point every 2 h. The test results are shown in Figure 7 (a). The average indoor illumination in winter and summer was the highest at 11 a.m., at 632 and 1156 lx, respectively, and the lowest was at 5 p.m. at 22.9 and 132 lx, respectively. Although the average indoor illumination in summer was higher than that in winter, the uniformity of illumination was very low. At 11 a.m., the illumination in S7 was 33 times that in S4. The variation range of indoor illumination uniformity was 0.18–0.34 in winter and 0.13–0.19 in summer, which is much lower than the standard value (0.7). Figure 7(b) and (c) show the variations at different measurement points from south- to north-facing in professional classrooms during different periods of winter and summer. The average illumination in the S-zone of the classroom was higher than that in N-zone, and the illumination was higher in areas closer to the window. The on-site test results indicated that the indoor lighting in the classroom was considerably uneven, and the quality of the natural light environment was poor.

Owing to the influence of daily climate and the position of the sun, the measurement of the natural lighting condition of the entire classroom using only a day’s test data was difficult. Therefore, a model of the classroom of manual drawing was established to simulate natural lighting conditions indoors throughout the year. Considering the grid surface 0.75 m high from the ground as the measuring surface, DA_450lx, UDI_450lx-1000lx and ASE_1000lx,250h were measured, and the results are shown in Table 1. During working hours throughout the year, the overall illumination of the classroom of manual drawing reached 450 lx, 54.71% of the time. The average value of UDI_450lx-1000lx was 36.97%. Combined with the distribution of UDI_450lx-1000lx, as shown in Figure 8, the lighting conditions in the middle of the N and S areas were the best, whereas in the window area, owing to the high intensity of natural lighting, the illumination of the area was higher than 1000 lx. The aisle area was deep and lacked natural lighting, which resulted in low illumination. ASE_1000lx,250h was 22.76%, which means that the user would experience visual discomfort most of the time. Therefore, in the natural light environment of a professional classroom, it is necessary to improve the high-intensity local daylighting in the window and the low amount of daylighting in the middle area of the professional classroom.

Table 1.

Simulation results of the current situation of indoor light environment in classroom.

Dynamic lighting index	Simulation result (%)
DA_450lx	54.71
UDI_450lx-1000lx	36.97
ASE_1000lx,250h	22.76

Parameters of reflector and louvre components

According to the current situation survey and natural light environment simulation results, the indoor natural light illumination in classrooms of this major is significantly uneven, often failing to satisfy the learning needs of students. Therefore, it is necessary to implement appropriate measures to improve the lighting environment. With technological advancements, various devices and technologies have been employed in architectural lighting to regulate the amount and direction of the incoming light, thereby achieving effective daylight control. Common control elements include reflectors and louvres.^36–39 Reflectors are operated based on the principle of reflection by redirecting natural light towards the ceiling. This helps enhance illumination in deeper areas of professional classrooms while ensuring uniformity and reducing glare near windows. Louvres are dynamic light-control devices that adjust daylight penetration through height adjustment and angular rotation. Double-silver low-E glass was selected for the louvre, which has the structural feature of setting up two layers of silver with a light transmittance of 50%.^40–43 This can reduce the solar radiation rate, avoid excessive light transmission and cause dazzling situations, and ensure clear viewing from indoors to outdoors without obstructing the view outside the window. In this study, a design integrating both a reflector and sunshade louvres was adopted. The reflector was positioned inside the south window with a horizontal extension capability while incorporating an embedded louvre close to the window glass at its bottom, as shown in Figure 9(a). Scholars have explored different degrees of optimisation for reflective components in classrooms and provided reference parameters.^44–46 However, because many studies have focused on specific spaces, their parameter values may not be applicable in this case. Henceforth, based on existing window conditions, reflector heights were set at 1.9 and 2.0 m with the width set to three values: 0.7, 0.85 and 1.0 m. The louvre spacing was 0.015 m, the louvre width was 0.02 m, the louvre thickness was 0.001 m, the reflectivity was 60%, the distance from the centre axis of the louvre to the wall was 0.1 m, and the louvre angles were set to five values: 30°, 45°, 60°, 75° and 90°, as shown in Figure 9(b). Based on the above parameters, Figure 10 shows 30 parameter combination schemes. This study focused on parameter combinations to improve the quality of natural indoor lighting.

Table 2 shows the variation trends of DA_450lx, ASE_1000lx,250h and UDI_450lx-1000lx in different parameter combination schemes, and Table 3 shows the distribution of UDI_450lx-1000lx in professional classrooms. From the results of the DA_450lx index of the autonomous daylighting threshold, compared with the working condition without the reflective plate and louvre components, the DA_450lx value was smaller, and the overall change range of the DA_450lx value was 40%–60%, that is, during the working hours, the proportion of the time when the indoor illumination reached 450 lx varied between 40 and 60%. In general, DA_450lx when the reflective plate height was 1.9 m was 6.5% higher than that when the reflective plate height was 2.0 m. When the reflective plate height was fixed, the higher the width, the lower the DA_450lx value. When the width was increased from 0.7 to 1.0 m, the autonomous daylighting threshold DA_450lx was decreased by 6.8%–7.5%. When the reflective plate height and width were fixed, the DA_450lx value of the autonomous daylighting threshold was increased with the louvre angle. Moreover, when the reflective plate height was fixed, the larger the reflective plate width, the greater the increase in the DA450 lx value with the increase of the louvre angle, which was 25.6, 29.2 and 32.7%, respectively. Therefore, the DA_450lx after adding the reflective plate and louvre internal shading was smaller, and with the reduction of the reflective plate height and width, the DA_450lx value was increased; that is, the percentage of the working surface illumination exceeding 450 lx during the working hours of the year depends on natural lighting.

Table 2.

Presents the numerical variations of DA_450lx, UDI_450lx-1000lx and ASE_1000lx,250h under different parameter combination schemes.

Table 3.

Calculation results of multi-objective optimisation UDI_450lx-1000lx.

The UDI_450lx-1000lx index results of effective daylight illumination indicated a decrease in the UDI_450lx-1000lx value compared to the working condition without the reflector and louvre components. The inclusion of a reflector enhances the local light environment around the window and reduces the glare. When the height of the reflector was set at 1.9 m, UDI_450lx-1000lx value was slightly higher than that when it was set at 2.0 m. In addition, with a fixed reflector height, reducing the width led to an increase in the UDI_450lx-1000lx value; for instance, decreasing the width from 1.0 to 0.7 m resulted in an 8.2% increase in this value. When the height and width of the reflector were constant, the UDI_450lx-1000lx value was increased with an increase in the louvre angle. Furthermore, maintaining both the height and width constant for the reflector, and increasing the louvre angle also contributed to an increase in UDI_450lx-1000lx value. Considering the reflector with dimensions of 1.9 m (height) and 0.7 m (width), varying louvre angles within a range of 30–90° demonstrated a significant upward trend in the overall UDI_450lx-1000lx value of indoor space. This is particularly noticeable around windows, where this value can reach up to 50%, as shown in Table 4. Therefore, despite observing a decrease in the UDI_450lx-1000lx after incorporating the reflector and internal shading louvres, optimising these elements by reducing the panel size while increasing the louvre angle would allow for more time spent within the desired illumination level range of 450–1000 lx during operational periods throughout the year.

Table 4.

Indoor illumination distribution after adding reflector and louvre components in the south window.

According to the ASE_1000lx,250h index results of annual sunshine hours, although the values of DA_450lx and UDI_450lx-1000lxx were decreased after incorporating reflector and louvre components compared to natural lighting conditions in professional classrooms, the ASE_1000lx,250h results satisfied comfort standards with an average reduction from 22.77 to 7%. The standard range for comparison was adjusted from discomfort to comfort.

Based on the aforementioned analysis, different combinations of parameters exhibit distinct variations in the daylighting index. Therefore, to determine the optimal parameter combination, a comprehensive comparison of the dynamic index results of 30 schemes is necessary. The calculation results for these 30 schemes were input into MATLAB for the simulations. Following the principle that higher values of DA_450lx and UDI_450lx-1000lx indicate better performance, whereas lower values of ASE_{1000lx, 250h} are desirable. The final selected position was determined using the scatter function algorithm, as represented by the red solid coordinate position in Figure 11. In Figure 11, the best position points corresponded to favourable values of DA_450lx, UDI_450lx-1000lx and ASE_{1000lx, 250h}. Specifically, when this parameter combination was selected, indoor desktop illumination exceeding 450 lx during working hours accounted for approximately 45.37% of the total time, indoor desktop illumination within the range of 450 to 1000 lx constituted an average of approximately 31.98% during working hours, and annual direct solar illumination exceeding 1000 lx with cumulative hours reaching 250 h occupied only 6.36% area, which is a significant reduction of 72% compared to previous conditions. Consequently, the optimal parameter combination scheme for reflector and louvre components consisted of a reflector height of 2 m, width of 1 m and louvre angle of 75° was adopted.

Discussion

Analysis of indoor illumination and illumination uniformity

A parameter scheme for the reflector and louvre combination suitable for the south-facing window of the classroom is presented. Based on the simulation results shown in Figure 11, while the ASE_1000lx,250h indices were reduced to a moderate level of visual comfort, there was a significant decrease of 17 and 13.5% in DA_450lx and UDI_450lx-1000lx respectively, indicating that the inclusion of reflector and louvre components would greatly enhance the overall indoor visual comfort, and would also affect the overall illumination levels. However, these results were derived from an analysis of dynamic daylighting throughout the year. Thus, further verification is required to assess specific light conditions on individual days. For illustration purposes, simulations were conducted during the summer and winter solstices between 8 a.m. and 4 p.m., with calculations performed every 2 h.

The corresponding distributions of indoor natural lighting illumination are presented in Table 4. On the day of the summer solstice at 8 a.m., only natural light was utilised, resulting in an indoor illumination level of only 100 lx, necessitating immediate supplementation with artificial lighting. Therefore, an optimal combination of lighting environments should be employed. In other periods under natural light, there was a noticeable overall improvement in the indoor illumination, ranging from 700 to 975 lx. In particular, the local illumination near the window in area S was significantly enhanced, and the average uniformity of the illumination was at 0.72. On the day of the winter solstice, at 8:00 a.m., the illumination fell drastically to approximately 20 lx, making it insufficient for fulfilling indoor learning requirements, thus demanding complete reliance on artificial lighting environments. In both N (10 a.m. and 4 p.m.) and S (4 p.m.) areas, the average illumination fell below the standard threshold of 400 lx, indicating inadequate levels that necessitated additional artificial lighting support. During this period (10 a.m. to 2 p.m.) in area S, numerous locations still experienced localised illumination reaching up to 2000 lx, requiring effective implementation of shading facilities primarily through artificial lighting.

The above results show that even if the reflector and louvre components were adopted, there were still certain cases of excessive illumination, low illumination and poor uniformity of illumination in the entire indoor space throughout the year, owing to the change in solar illumination. This shows that the classroom lighting environment cannot satisfy learning needs by relying only on natural light during the daytime, and a certain amount of artificial light was needed at times. According to the above-mentioned simulation calculations of the summer and winter solstices, Table 5 shows that different forms of light environments were adopted during different periods of the day and in different regions. During the daytime, the proportion using only natural light was 30%, the proportion using the combined light environment was 45%, and the proportion using the artificial light environment was 25%. Therefore, a better-quality light environment can only be obtained by comprehensive utilisation and mutual supplementation. This research team has also proved in a previous study¹³ that under a combined light environment in the daytime, people would experience the space as brighter, more spacious and relaxed. Therefore, different forms of light environments should be adopted during different periods in the classroom.

Table 5.

Forms and periods of light environment corresponding to the summer solstice and winter solstice.

Time	The region	8:00	10:00	12:00	14:00	16:00
Summer	N	Combined light	Natural light	Natural light	Natural light	Natural light
Summer	S	Combined light	Combined light	Combined light	Combined light	Combined light
Winter	N	Artificial light	Combined light	Natural light	Natural light	Combined light
Winter	S	Artificial light	Artificial light	Artificial light	Artificial light	Combined light

Improvement measures for windows facing other directions in the classroom

For the east-facing window of the classroom, Table 4 shows that during the morning hours, particularly from 8 a.m. to 10 a.m., the location near the east-facing window had high illumination and strong direct sunlight; therefore, no drawing desk was arranged there (Figure 3(a)). To further optimise the lighting environment in the area, a reflector was installed in the upper-middle part of the east-facing window, which served as a sunshade. Simultaneously, the corresponding ceiling position in the eastern classroom was coated with a high-reflection-coefficient material, as shown in Figure 12. After adopting this measure, the light was reflected to the indoor ceiling according to the different heights of the sun during winter and summer and was further reflected to a position far away from the window indoors. The illumination near the window was not extremely high.

For the north-facing window of the classroom, Table 4 shows that owing to the lack of direct sunlight in the northern direction, the illumination on the north-facing desktop was relatively low in natural light environments. However, its advantage was that there was no glare. Therefore, we recommend to increase the artificial lighting to supplement the illumination on the desktop near the north-facing window.

Lighting improvement measures based on the enhancement of indoor lighting quality

Because the classroom must adopt the form of a combined light environment or an artificial light environment during certain periods of the day, artificial lighting is necessary, and the lamp on the study table is the main lighting source. At present, the indoor lighting fixtures in the classroom consist of 18 LED lights with a power of 34 W, and the hanging height from the desktop is 1.5 m. The illumination of the combined light environment in the simulated zones S and N in the open state of the lamp is presented in Table 6. The average illumination of the space in the N and S areas was greater than 1000 lx. When the illumination was too high, fatigue in the students was noted during long-term study and work. Therefore, illumination needs to be reduced. The illumination uniformity was 0.55, indicating that indoor illumination was uneven. Combined with the illumination distribution chart, the overall horizontal layout of the lamps was biased to the east of the professional classroom, and the illumination in different positions in the space was not uniform. The low hanging height of the lamps has led to severe glare on the working surface. Therefore, the hanging height of the lamps and the power of the light source must be adjusted.

Table 6.

Indoor illumination when the lamp is hung 1.5 m high and the lamp power was 34W.

Simulation project		Simulation result
Illumination (lx)	N-zone	1117
Illumination (lx)	S-zone	1043
Illumination uniformity		0.55
Illumination distribution

In the horizontal direction, the overall position of the lamps was moved towards the west by 0.65 m, making the distribution of lamps in the space symmetrical. In the vertical direction, the height of the lamps was increased and the two parameters were set to 1.7 m and 1.9 m. The simulation results, when the height of the lamps was 1.7 m, are listed in Table 7(a). The average illumination of the space in the N and S areas was decreased; however, the average illumination was still greater than 1000 lx. The illumination uniformity was 0.77, which satisfied the standard. The simulation results when the height of the lamps was 1.9 m are listed in Table 7(b), and the illumination uniformity was 0.81. Compared with the values when the heights of the lamps from the table were 1.5 and 1.7 m, the illumination uniformity was increased by 29.10 and 14.08%. The increase in the height of the lamps from the table, has effectively increased the illumination uniformity of the classroom of manual drawing. However, the average illumination of the N and S areas was still greater than 1000 lx. Therefore, in addition to considering the heights of the lights and lanterns, the power of the lamps should be simultaneously adjusted. The illumination of the lamps with powers of 30 and 26 W was calculated, and the illumination results are shown in Table 7(c) and 7(d). The average illumination of the space in the N and S areas was controlled to be within 450 to 1000 lx. In terms of illumination uniformity, when the lamp power was 26 W, the illumination uniformity was larger, reaching 0.86. Therefore, the lamp power should be adjusted to 26 W, and the colour temperature should be 4500 K.¹⁴

Table 7.

Combined light ambient illumination of different luminaire positions and power parameters.

Set parameters	(a)	(b)	(c)	(d)
Luminaire hanging height (m)	1.7	1.9	1.9	1.9
Lamp power (w)	34	34	30	26
N-zone (lx)	1145	1048	973	903
S-zone (lx)	1109	1065	981	887
Illumination uniformity	0.71	0.81	0.82	0.86
Illumination distribution

Intelligent dynamic control mode of optical environment

Through the analysis of the light environment in different areas of the classroom of manual drawing in different seasons and different periods, to further flexibly regulate the indoor light environment to achieve the optimal effect, the daylight environment of the classroom was dynamically regulated by the intelligent system, which can make full use of natural light, and also improve the quality of the indoor light environment. The parameters corresponding to the different time periods were input for timing control. The intelligent control mode is shown in Figure 13. The details are as follows.

(1) When the manual drawing classroom was in a natural light environment or a combined light environment during the day, the reflector improved the light intake of the central space of the professional classroom, and the louvre facility improved the situation in which the illumination of the peripheral position of the window was too high. At this time, the reflector was in the stretching state, with a height of 2 m, width of 1 m and louvre angle of 75°. The lamp power was 26 W.

(2) When the classroom of manual drawing was in an artificial light environment during the day, the reflector was in the withdrawal state and the louvre angle was 90°. The lamp power was 34 W.

(3) When the classroom of manual drawing was in the artificial light environment at night, the reflector was in the withdrawal state and the louvre angle was 0°. The lamp power was 34 W.

Conclusion

Considering the current lighting conditions in a manual drawing classroom at a university in Beijing, this study proposes various optimisation and improvement measures using dynamic simulation methods. The key findings are as follows.

(1) A single strategy cannot fully satisfy the requirements of classroom lighting environments. Different lighting environments should be utilised based on the seasons, time periods and specific areas within specialised classrooms during daytime activities.

(2) To optimise the natural light environment, five windows were improved in three directions. For the south-facing window, reflector and louvre components should be installed. The reflector should have a height of 2.0 m, width of 1.0 m and the louvre angle should be set at 75°. For the east-facing window, installing a reflector in the middle and upper parts of the window is recommended. For the north-facing window, addition of an artificial light is recommended to compensate for insufficient illumination. The indoor illumination level and lighting comfort can be ensured by optimising and controlling five windows with different orientations.

(3) To enhance the indoor lighting quality of specialised classrooms, natural light should be combined with artificial lighting during the daytime while considering further optimisation of lamp light sources. Symmetrical distribution of lamps horizontally at a vertical distance of 1.9 m (0.4 m higher than before) with a power output of 26 W can improve lighting uniformity.

(4) The recommended proportions of natural, combined and artificial light environments were 30, 45 and 25%, respectively. The reflector and louvre components, along with the lamp power regulation considerations, were integrated into an intelligent control mode.

Footnotes

Acknowledgements

The authors are thankful to all subjects for their participation in the investigation and for providing information on their perception and description of the indoor environment.

Authors’ contribution

Xiaohui Du conceived the idea, collaboratively wrote, reviewed and edited the paper. Sijia Zhao participated in writing, mainly hosted and organised the simulation and experimental test. Shijing Hu was responsible for the paper format editing. Siyu Song assisted in the experimental test and data compilation.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was financially supported by Beijing Jiaotong University Training Program of Innovation and Entrepreneurship for Undergraduates (202510004151); the National Key R&D Program of China (NO. 2023YFE0102100).

ORCID iD

Xiaohui Du

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