Determining Artificial Lighting Criteria for Traditional Mud Buildings and Their Impact on Aesthetic Values and Functional Aspects (A Case Study: Historical At-Turaif District)

Abstract

This study aimed to analyze the lighting design in selected historical sites. Lighting plays a significant role in reflecting symbolic, functional, and aesthetic values. Our study found that there is no special recognition for mud buildings’ outdoor lighting standards, so we analyzed the lighting design in a case study approved by the Diriyah Gate Development Authority. We developed lighting criteria and tested the effect of the building surface on these criteria, to be used as a reference for lighting local mud heritage buildings. This study used a mixed methods research framework encompassing both qualitative and quantitative data. For the qualitative data, a descriptive–analytical approach was used to list all the criteria found in the literature for historical and heritage buildings, as well as site visits and observations for the selected mud building. The quantitative data contained the dimensions identified in the first phase to develop and test the preferences of lighting criteria illuminance and correlated color temperature (CCT). A computer simulation was created to derive the outdoor lighting standards, and a questionnaire was developed to assess clarity, sensitivity, and preferences. The findings revealed that participants mostly preferred higher illuminance and warm temperature was preferred over other temperature options. The manuscript concludes with some recommendations for future studies.

1. Introduction

Urban lighting has evolved from a functional tool for safety and orientation to a means of enhancing the aesthetics and cultural significance of architectural monuments and historic sites. This has led to the adoption of new lighting technologies in cities worldwide and increased interest from researchers and designers in defining new design methods and measurement models. Historical and cultural sites are seen as essential for preserving collective memory and a sense of place, and guidelines and recommendations for lighting heritage sites have been established by organizations such as UNESCO. Five sites were included in the Kingdom Vision 2030, including At-Turaif historical district.

This study’s objectives are to derive outdoor lighting criteria and compare them to those applied in the selected case study (Prince Saad Bin Saud Palace), located in the At-Turaif historic district, and study-specific preferences of the luminance and CCT as it consists of warm, cool, and neutral temperatures, so as to understand those most suitable and preferred for heritage local mud buildings. A 3D model was built, and the mud specification in terms of color and light reflection was applied to the selected case study using computer software. A questionnaire was prepared that considered the viewers’ preferences. This aimed to aid the primary goal of this manuscript and identify suitable aesthetic lighting designs (illuminance and CCT) in mud heritage buildings that consider such preferences.

2. Problem Statement

The lighting of historical sites is an important way to enhance the functional and aesthetic values of heritage buildings. Architects and researchers have focused on this matter but have not considered the building surfaces’ type and texture, especially in historical sites with mud heritage buildings, and none have been found in the literature. This study aims to shed light on the impact of artificial lighting on both the aesthetic values and functional aspects of traditional mud buildings. To achieve the objectives of this manuscript, we aimed to establish preliminary guidelines that can serve as a valuable resource for future designers and architects working with mud heritage buildings and ensure a harmonious integration of artificial lighting within the historical context while preserving the unique charm and cultural heritage of these architectural treasures.

3. Literature Review

In the context of traditional mud buildings, there is a need to delve into the exploration of sightseer behavior and preferences to gain a deeper understanding of their motivations, expectations, and satisfaction levels with the destination. Altassan emphasized the significance of investigating these aspects, particularly in relation to traditional mud buildings, to inform the determination of appropriate artificial lighting criteria [1].

Night lighting plays an important role in improving the night scene’s expressive aspects and confirming the architecture’s identity. To obtain better lighting design results, designers should adopt a clear philosophy of light design, lighting the exterior of a building with all its components through indirect light expression, planning the light design through the early stages of the project design, considering the surrounding environment in the light design, and using different luminaires to highlight the element’s aesthetics and avoid boredom. These recommendations have been made for designers to follow to obtain better lighting design results [2].

Light is a vital source of energy and a divine blessing connecting sight and life. With advancements in science and technology, Sedky & Yahya argued that designers have to rediscover the potential and aesthetics of light [3]. Designers can balance the functional role of light within artworks with its aesthetic by studying its characteristics and interactions with various formation data. Artificial light plays a significant role in highlighting aesthetic values in designed artifacts by displaying static or dynamic formations, showcasing perspective depth, and showcasing surfaces. Therefore, designers should concentrate on subject components, use light and shadows to highlight unit formations and materials, add an aesthetic touch to shapes, and deepen the sense of space, vacuum, and formation units.

Madkour has found the appropriate strategies for lighting heritage buildings and raising awareness of their roots. The study suggested that the best result in designing light features is mainly obtained with collaboration between the architect, lighting engineer, and archaeologist. It also suggested some recommendations for designers to consider before starting to light heritage buildings: place the luminaires close to the vertical surface to deepen the shadow on the surface texture. Dark materials require higher luminance levels, while light-colored materials require less. Warm light is used for warm stonework and brickwork; cool light sources are for white stone or concrete [4].

The surrounding environment should be studied along with its level of light. The right lighting design should consider the four diminutions of light: light direction, luminance, CCT, and time [5]. Important considerations must be given for the lighting equipment; they should be hidden as much as possible.

Two types of lighting (floodlighting and spotlighting) and their effect (light dynamics and light color) were investigated to measure their influence on aesthetic, emotional, technical, and economic aspects. A study suggested using small-sized luminaires with high luminous efficiency (using LEDs) to mask them and maintain their effect [6]. However, when using LED, studies and calculations should be performed using a suitable methodology to provide lighting strategies for the future [7]. To emphasize buildings’ shapes and their surroundings via light, shade, and gradation of light, the study of the site and surrounding areas, observer view, physical shape, form via light shade, and shadow should be performed.

A study by Suriyothin [8] confirmed that good exterior lighting can offer environmental and psychological benefits for viewers. It suggested some particular recommendations for exterior lighting that add prestige, safety, symbolism, and recognition to the place: a careful analysis of the building, the distance of the viewer, the three-dimensional quality of the building, accessibility to luminaries, the type and quality of the equipment, the way the luminaries will look during the day, the avoidance of glare, following the guidelines for light pollution, the degree of reflection, and maintaining the luminance ratio of the building and its surroundings at less than 20:1. An exception is made for buildings located in commercial areas or where night activities occur.

The study stated that the most important details for heritage building exterior lighting are to consider the building’s main character, age, and historical significance. Lighting from the ground or highlighting from concealed luminaires mounted on the structure can have a stunning effect. Work should be performed with the project architect, lighting designer, and archaeologist, and timing should be limited to only when needed or required. Luminance in historical and heritage buildings ranges from 13–16 cd/m².

The study recommended four techniques for façade lighting: front lighting, backlighting, side lighting, top lighting, and up lighting. Front lighting decreases visible shadows and minimizes surface details, while backlighting emphasizes the overall shape. Side lighting increases the sense of dimension, depth, volume, shape, texture, and pattern, and produces more shadows. Top lighting or down lighting reflects the light as it is during the daytime, while up lighting is an unnatural technique used to create drama. Up lighting highlights a specific architectural element but generally does not provide as much ambient light as down lighting.

Zakariaa & Bahauddin argued that the most important details for lighting historical sites include analyzing the surroundings, planning comprehensively, and educating designers about the medical, environmental, and biological factors that impact humans and other creatures [9].

To reduce light pollution, designers should use luminaires with reflectors and clear covers, asymmetric beam floodlights with asymmetries adapted to the area to be lit, keep the main beam angle of all lights directed toward any potential observer by not more than 700, maintain the luminous flux at a level not higher than necessary, use products with adaptive controls, choose luminaires for which the spectrum has the lowest impact on night sky quality, use LEDs with low correlated color temperature, and keep light flux completely intercepted by the building façade. Luminous flux should be reduced when they no longer fulfill their function and can be connected to a timer system.

A study performed by Bista, et al. [10] for Pagoda-style architecture in Nepal presented a deep analysis of the malpractices in the lighting of the ancient building. It proposes an innovative way of lighting, which was investigated and tested in a case study. The developed approach has been selected via a subjective preference approach, and recommendations have been made and listed in

Table 1. List of recommendations (reprinted from Ref. [10]).

Problems	Recommendations
Lack of standards for specific areas and construction materials	National standards should be developed for the illumination of such heritage sites based on their locality, architecture, environment, construction materials, and religious beliefs and importance. An extensive experimental and subjective preference analysis should be conducted for the specific type of construction materials, architecture, environment, etc., so that the development and deployment activities lie in uniform and effective ways.
Conflicting interests amongvarious groups	The perspective of both designer (light engineer) and the experts on heritage architectural buildings must be matched. A concrete national standard can help to resolve conflicts and implement the lighting technologies with the finest mode. However, the standard must be set with the participation of all group of experts including the local participations.
Penetration of modern productsand technologies	Some innovative concepts and technologies must be introduced, which do not affect originality and the spiritual, religious, and visual values. Flexible, controllable LED technologies with specified spectra and intensities can be recommended for specific case areas and material types. The methodologies and the outcomes of this study can be followed to illuminate the specific pagoda-type temples within the nation. Similar methodologies can be followed to illuminate other monuments all around the world (the outcomes may vary for different types of architecture and construction materials).
Safety issues	Standards on electrical components and layouts must be defined so that no fault issues affect the sensitive parts of the heritage monuments. Since most of the Nepalese monuments are made up of wood, a small fault can be fatal for the whole structure. Similarly, protective equipment must be included in the list since Nepal is in a lightning-prone zone. Similar cases can also be found in other countries; a definite standard must be practiced for heritage illumination all over the world.

. These recommendations explicitly target the Nepalese heritage site; with the smart recommendation, the case study could be designed even better.

The most important details in this text are the points to consider when designing heritage building lighting. These include using the right electrical layout and type of luminaire according to its efficiency in a suitable space, picking the right correlated color temperature for the exterior and interior spaces, supporting and reflecting the main design concept, and focusing more on the building’s exterior main features such as texture, form, color, and construction. LED is considered one of the most excellent types of light for exterior and interior spaces due to its low cost and wide range of colors. The night light design should support and reflect the main design concept and focus more on the building’s exterior main features such as texture, form, color, and construction. Therefore, researchers and designers should study the effect of night light designs in order to enhance night vision and reach a better architectural environment. It is important to balance the amount of light needed to show and enhance the building’s architectural elements and the electricity used to light the site. It is also important to avoid brightness by using sufficient illuminance and applying gradual transition levels of light between the internal and external periods. Additionally, it is important to pay more attention to illuminating tourist and archaeological landmarks thoughtfully and creatively to highlight them and attract internal and external tourism. This will help draw attention to the history and civilization of historical monuments in local architecture.

One study recommended further studies to understand the reasons behind ignoring artificial light when designing [11]. It also highlighted the need to understand the psychological impact of lighting on users. The lighting criteria found in many institutions specializing in lighting design for interior or exterior spaces are illumination level, parallel illumination, reducing glare, the direction of shades and shadows, and light color. The study [12] identified suitable design strategies and developed a recovery project for a case study in the Abruzzo Region, Italy. This project was evaluated from an economic point of view, through life-cycle cost analysis (LCCA), and from an environmental perspective regarding CO₂ emission reduction. This research contributes to implementing the 2030 Agenda and illustrates a multidisciplinary framework that was developed to achieve the correct design of lighting systems in urban contexts of historical value, starting from the analysis of the current state.

The paper [13] concluded that using lighting techniques for façades should not cause any damage to the walls, and light should be considered the Fourth Dimension of architecture. Light fixtures should be carefully selected and installed with concern for the exterior elements of the mosque while being suitable for the textures of the walls. Illuminance should be adjustable, and LED-induced light should not be too dazzling. Detailed drawings and explanations should be provided for applying lighting installations, including the power source and connections. Courtyard entrances, rectangular windows, and other parts of the mosque should be highlighted using appropriate lighting elements for the structure. The placement of luminaires should be checked to avoid excessive interference and unnecessary interventions, and the project should be completed with minimal intervention. LED technology should be selected for its economical and energy-saving properties, and luminaires should be dimmed or turned off after a specific time at night. Installation and armature should not disturb or interfere with the appearance of any part of the mosque.

The ‘Ruta de los Rios de Luz’ lighting project was developed in 2011 by the Spanish city of Valladolid to use light for tourism purposes [14]. The designers and local authorities worked together to conceptualize the use of illumination for tourism purposes. This project shows how lighting has changed from being a functional and pragmatic component of a cityscape to becoming a theatrical device essential for staging an exciting urban experience for residents and tourists. It is important to integrate the aesthetic and technical aspects of light with a more critical examination of the performative effects that spectacular forms of illumination may have on the every-night experience of the city.

Small-scale historic urban settlements need special techniques and strategies to achieve quality lighting, cultural reinforcement, and tourist attraction. Kopanari, Sigala, & Skandali recommended the following techniques: wall-mounted floor washers with asymmetric light distribution, higher average illuminance levels in low-level lighting spaces, wall-mounted luminaires with an asymmetrical beam, wall-mounted up-light in high-level positioning, landmarks to be highlighted with discreet illumination, and open spaces and squares to be illuminated with area diffuse lighting [15]. These techniques are important for achieving quality lighting, cultural reinforcement, and tourist attraction.

Wang, et al., studied the use of colored light in historic buildings. They found that the most common types of lighting were interior lighting, floodlighting, point light source, and line light source. The most common colors used were natural colors of stones and exterior wall tiles. This suggests that the use of colored light is unscientific and lacks theoretical support [16]. Additionally, they showed that combining linear light source lighting and three different color thermal light sources can easily arouse people’s traditional, warm, and romantic color light emotions. It was similar to the experiment performed on the pagoda-style architecture of Nepal, as [10] also studied the effect of light sources on the appearance of the selected material (bricks, stone, and wood). As a result, these recommendations are shown in Figure 1.

In conclusion, artificial light has a wide range of impacts on many case studies presented in the literature. Many researchers have agreed on the need for lighting design with respect to the different aspects of lighting. For example, some divided them into four main aspects: functional, physical, biological, and aesthetic, and others have only focused on certain aspects [15]. In contrast, refs. [12,13,14] focused more on the economic, environmental, and aesthetic aspects. The most frequently considered aspects in the literature are the aesthetic, functional, and economic aspects.

The lighting criteria found in the literature for historical heritage buildings were designated for different sites and different buildings’ exteriors. In most case studies, building materials were brick and concrete, and some included wood and steel. However, less than 30% of these papers discussed the impact of the texture of the building exterior on the lighting criteria. Additionally, none were performed for lighting mud heritage buildings, and there are no specific criteria for lighting mud heritage buildings, including the impact of the mud surface and color on the lighting criteria. It is important to consider the impact of artificial light on humans and the environment. Furthermore, most papers have discussed the negative effect of using artificial light without a previous study, and most of the papers that suggest lighting designs have used light simulation programs, such as Relux software [10]. Dialux (5.8.0.39677) software, produced by DIAL, is the most popular software used for light simulation and was used by [12,15].

4. Research Methodology

The methodology used was a mix of methods, and a research framework encompassing both qualitative and quantitative methods and measures was used to enhance the examination of the research questions. We employed a sequential exploratory strategy, which incorporates the collection and analysis of qualitative data, followed by the collection and analysis of quantitative data. In the first phase, a qualitative multi-method was used to explore the various dimensions of the night artificial lighting at historical sites and the At-Turaif district. The second phase contained the dimensions identified in the first phase to develop and test the preferences of lighting criteria (illuminance and CCT), to better understand the visitor’s lighting preferences for mud heritage buildings in historical sites.

The qualitative phase of this research aimed to understand the lighting criteria listed in the literature for historic sites and heritage buildings. Site visits were conducted to observe the criteria used, which helped develop a survey instrument to operationalize the qualitative results.

The selected case study was Prince Saad Palace, a mud heritage building at the At-Turaif historical site in Diriyah, 20 min northwest of Riyadh’s city center. It is a UNESCO site and is part of the Kingdome Vision 2030 project to enhance its visual quality and visitor experience [17]. The heritage buildings on the site are built of mud and are suitable for the study requirements. Site visits were conducted to collect data related to the lighting design and surface characteristics of the palace. Tools such as a Dr. Meter, Sensegood spectrophotometer, and Gloss meter were used to measure the illuminance, mud color, and glossiness of the mud.

The second phase of the study combines the dimensions identified in the first phase to develop and test the preferences of lighting criteria (illuminance and CCT). The quantitative phase went through many steps, including studying the findings from the first phase, building a 3D model for the selected case study (Prince Saad Palace) at the At-Turaif historical district, and reflecting the light in the actual site in the 3D model using a computer light simulator program.

A BIM Autodesk software (Revit 2021) was selected to build a 3D model due to its easy export/import capabilities. DiaLux evo 10.1 software was chosen for light simulation due to its compatibility with the requirements of the study (designed for artificial lighting simulation and exterior artificial light simulation, compatible with Windows, gives lighting calculations, and allows the creation/import of 3D models).

In addition, two questionnaires were designed by SurveyMonkey to understand visitors’ preferences for two artificial lighting criteria (illuminance and CCT) on traditional mud buildings related to aesthetic values and functional aspects. The web-based questionnaires were administered through social media in Arabic/English to help cover a wider range of participants.

The first questionnaire was performed to help set a fixed percentage to increase and decrease illuminance. After a lighting specialist recommended adding 60%, the questionnaire investigated this percentage by including three illuminance levels to be tested. This questionnaire included four questions for each question; an image of the original illuminance level was displayed along with another image that showed an increase in illuminance by 30%. The second question showed an increase by 60%, then the third by 90%, and participants were asked to declare which one was higher or if they viewed the illuminance as equal in both images.

The second questionnaire was built to study the effects of the two artificial lighting criteria (illuminance and CCT) and to understand the preferences for these criteria. The questionnaire had three sections. The first section covered the demographic questions. The second section investigated the health status of the participants, which might affect their vision. In addition, this section included a colorblindness test; according to [18], the two colors used (red and green) are the colors which colorblind individuals most often struggle to differentiate. Therefore, participants were asked to choose these colors out of the rest of the colors displayed. Finally, the third section consisted of three questions. The first question showed a group of images with different light intensities (a total of five images with a 60% illuminance increase in each image), in which participants were asked to choose the image they thought had the best lighting intensity, while the second question showed a group of different CCTs (warm/2700 K, neutral/4000 K, cool/5700 K) displayed in the selected illuminance, and the last question was for comments if they had any.

5. The Case Study and Procedure

Prince Saad ibn Saud Palace was selected as a case study because its lighting system was approved by the Diriyah Gate Development Authority and Saudi Tourism Authority [19,20].

The palace is a prominent feature located in the At-Turaif district, which is a UNESCO world heritage site in Saudi Arabia [21,22]. It is in the northern part of the district and is one of the largest palaces in the area and was built to house Prince Saad and his family. Prince Saad was the son of Imam Saud the Great. The palace was designed to reflect the social status of the family and was built using traditional mud blocks, wood, stone, and gypsum. It has a wide traditional inner courtyard into which all the palace windows and doors open it, including guest rooms, making the inner courtyard work as the main circulation for the house. The palace is also known for its exterior courtyard attached from the southwestern side, which was used as a stable for horses and their needs. The palace’s exterior shows the famous traditional rectangular and triangle openings carved in its thick adobe walls, ending up with a series of triangles on the top of the wall. The palace is a significant attraction in the At-Turaif district and is distinguished from its surrounding areas due to its unique lighting system.

The case study procedure is structured into three distinct parts, each illustrating a specific aspect of the case study lighting design and procedure. As depicted in Figure 2, a comprehensive flowchart showcases the sequential steps undertaken in this chapter to obtain the proposed lighting design for the Saad Palace case study. Broadly, the three parts encompass the following:

• The first part encompasses the collection of relevant data pertaining to the site, including architectural information, the current lighting status, and the surface characteristics of the Prince Saad Palace. This section extensively covers details regarding the materials employed in constructing the palace’s exterior walls. The data necessary for this analysis were collected diligently during site visits.
• The second part of the procedure focuses on the practical application of the acquired data. The information gathered in the previous part serves as the foundation for building a comprehensive model, which is subsequently employed to simulate the proposed lighting design utilizing specialized software.
• The third part centers around the administration of a questionnaire that encompasses additional lighting criteria options specifically tailored for the Prince Saad Palace to understand the preferences related to lighting aspects.

5.1. Part I: Data Collection

Throughout the site visits, an extensive dataset was meticulously collected to facilitate the simulation of the proposed lighting system for the palace. This dataset encompasses a range of architectural attributes, physical dimensions, and external surface characteristics of the palace. Specifically, the following external surface features were meticulously documented: the intensity of light on the palace’s exterior, and the distinct characteristics of the external surfaces, including surface color and surface reflection index. By capturing these crucial details, we ensured a comprehensive understanding of the palace’s physical makeup, enabling an accurate and realistic simulation of the proposed lighting system.

The illuminance in the palace was taken using the lux Meter (LX1010B) device. The readings were taken from different parts of the building exterior but mainly targeted the main elevation (southern elevation), the side elevation (eastern elevation), and finally the fenestrations on the first floor of the palace. The readings were as follows: The main elevation: 320 lx, and the side elevation: 220 lx. Openings on the first floor: 80 lx. All readings were taken after nightfall between 9:30 p.m. and 10:30 p.m. The construction material used in the district of the case study is mud. Although mud is used all around the Kingdom of Saudi Arabia, the sources of the components of the material vary. Therefore, the surface characteristics vary from one area to another. Since the required details of the wall surface reflection index and color in the literature were unavailable, surface color and reflection were investigated during the site visits, as they have an important influence on the lighting design, which the viewer can easily recognize. Therefore, two different devices were used to collect the missing data (color and reflection); one was taken to the site and used there, and the other was off-site and required a wall surface sample collected during the visit. The results of both devices were used in developing the palace model in part two.

To obtain the surface color, a ‘Sensegood spectrophotometer’ was used to determine the color difference to ensure wall color consistency. The readings of the Sensegood spectrophotometer showed the following: Hex color code: cbb295; RGB: R—203, G—178, B—149; as shown in Figure 3.

For the reflection, a Gloss Meter was used on-site to determine the specular reflection gloss of the surface. The device version used after calibration was the HG268 Gloss Meter. The Gloss Meter was held next to the wall surface to measure reflection by projecting a set intensity and angle beam of light onto the wall and measuring the amount of light reflected at an equal but opposite angle. Five measurements were taken on different points of the wall surface in order to compare the results and make sure of the measurement’s result. The readings were the following: the reflection of all 20°, 60°, and 85° angles (0.4, 0.9, 0.0); to insert the reflection index in the computer modeling software, the number must be rounded up to (1) and be added as (1%) for reflection (glossiness).

5.2. Part II: Computer Modeling

Based on the data collected from the site, a 3D model of Prince Saad Palace and its lighting design was created using Revit for the 3D model construction, DiaLux for the lighting analysis, and 3D MAX for the image rendering. By using these three software, it was possible to reproduce the lighting of the actual site in the 3D model. Revit 2021 was used to build the model of Prince Saad Palace. On the property bar, the color of the wall surface was added as RGB (R 203, G 178, B 149), while the reflection (glossiness) was (1%). Once the collected data were added, the exterior appearance of the model changed with the new properties. After inserting all the additional data, the model was imported in 3D max to ensure that all the characteristics of the building surface matched the real site case study characteristics.

In the 3D model, the lighting design was applied according to the actual site. The lighting design was created by DiaLux, mirroring the exact light design from the actual site. The site had only one type of luminaire, which was applied in the 3D model. The applied type was the LED luminaire (1.2 m length and 5 cm width) and was almost 8 cm elevated from the ground along both elevations (south and east). This gave an upward light direction. As Figure 4 shows the applied type of luminaire and its location (Figure 4a) along with the result of computer visualization (Figure 4b,c), which reflects the actual site with an illuminance of 320 Lx.

This study focused on manipulating two main lighting criteria: illuminance and CCT. The temperature selected was based on the European Standard EN 12464-2:2014 Light [23] and on the numbers by (Meerwein, Rodeck, & Mahnke) [24]. Three scenarios were used, in which luminaires with the following correlated color temperature values were used to display in the survey: 2700 K, 4000 K, and 5700 K.

5.3. Part III: The Questionnaire

Two questionnaires were designed to study the effects of artificial lighting criteria (illuminance and CCT) on traditional mud buildings related to aesthetic values and functional aspects. In order to determine the optimal percentage for increasing and decreasing illuminance levels, a lighting specialist recommended adding 60% to each level, as it would be noticeable to viewers. Based on this recommendation, the survey questionnaire was divided into two sections. The first section included demographic data, while the second section consisted of four questions. Each question presented participants with two images: one with the original illuminance level and the other with an increased illuminance. The increases were 30%, 60%, and 90%. In addition, participants were asked to indicate which image had higher illuminance or if they perceived illuminance as equal in both images. Finally, a control question was included to ensure the accuracy of responses, which featured two images with the same illuminance level. Accordingly, the survey results aligned with the specialist’s recommendations, which helped greatly in determining the intensity level most viewers recognized. As a result, the second questionnaire was designed.

The second questionnaire had three sections: demographic questions, health status questions including a colorblindness test, and questions related to illuminance and CCT preferences. Participants were asked to choose the best illuminance and CCT based on the images provided and were allowed to provide comments at the end of the questionnaire.

The case study (Prince Saad Bin Saud Palace) was built and tested for five different illuminance levels to measure the visitors’ preferences. Each illuminance level had three different CCTs also to be measured. To provide more clarity about the varied levels of light and CCT mentioned in the questionnaire, their numerical values were included in

Table 2. The light details displayed in the questionnaire.

Variable	Changes	No.
Luminous flux	Level 1	880 lm
	Level 2	2200 lm
	Level 3	5500 lm
	Level 4	8800 lm
	Level 5	14,080 lm
CCT	Warm	2700 K
	Neutral	4000 K
	Cool	5700 K

. Nonetheless, during the light preference questionnaire phase, participants were presented with only pictures of the final light source results, which were created through computer simulation. This approach was intended to enable the participants to make their preferred choices for lighting and CCT based on visual representation, rather than relying on numerical values.

In accordance with the ethics and requirements for human participants, informed consent was obtained at the beginning of the questionnaire, and participants were informed that the results of their survey forms would be kept confidential. The survey questionnaire was administered on social media in Arabic and English and was active for one month until the number of participants reached the required sample size. After the survey procedures were completed, the collected data was analyzed in SurveyMonkey using its analyzing tools and also exported to Microsoft Excel for more statistical analysis.

The At-Turaif neighborhood, which has a rich historical significance, was recently opened to visitors. However, the lack of primary data made it challenging to estimate the number of visitors accurately. Therefore, a substantial number of potential visitors were considered, and the sample size was determined using the Steven K. Thompson equation [25]:

$$n=\frac{\mathrm{N}\left(p\left(1-p\right)\right)}{[\left(\mathrm{N}-1\right)\left(\frac{d^2}{z^2}\right)+p\left(1-p\right)]}$$

(1)

where:

n = Sample size.

N = Population size.

z = Confidence level at 95% (1.96).

d: Error proportion (0.05).

p: Probability (50%).

Once the questionnaire data were collected, they were analyzed and recorded in spreadsheets. To efficiently analyze data in various ways, SurveyMonkey’s Statistical Package and MS Excel were utilized for statistical analyses. Descriptive information on moderating variables such as age, gender, nationality, and educational level was included to provide a snapshot of the sample from which data was collected. Descriptive statistics, such as illuminance and temperature, were also recorded and organized using frequency tables. Analytical measurement tools were used to determine the relationship between variables and examine any significant differences between scores and the selected variables.

6. Results & Analysis

A comprehensive questionnaire was employed to gather pertinent information regarding lighting preferences based on specific criteria. To ensure inclusivity, the questionnaire was meticulously translated into both Arabic and English and subsequently disseminated through various social media platforms over a period of 3–4 weeks. The total number of responses received amounted to 457, but after careful screening, 63 responses were excluded. These exclusions comprised participants with pre-existing eye medical conditions or individuals who failed to complete the blindness test integrated into the questionnaire. As a result, a total of 394 valid responses were considered for the study.

The questionnaire itself consisted of 12 questions, strategically categorized into three distinct sections. The first section focused on capturing participants’ background information, while the second section aimed to ascertain any existing eye medical conditions among the respondents. Finally, the third section delved into participants’ preferences for various lighting criteria.

While the initial total number of responses reached 457, it is important to note that 58 responses were received from individuals with eye conditions, and an additional five participants failed the colorblindness test. Consequently, the study solely relied on the data obtained from the remaining 394 responses.

Table 3. Questionnaire first section responses.

Question	Number of Responses	Percentage
Q1. Gender
Female	232	58.88%
Male	162	41.12%
Q2. Age
Under 19	9	2.28%
20–29	178	45.18%
30–39	97	24.62%
40–49	52	13.2%
50–59	32	8.12%
60+	26	6.6%
Q3. Nationality
Saudi Arabian	337	85.5%
American	3	0.76%
Canadian	2	0.51%
Egyptian	1	0.25%
Filipino	1	0.25%
Iraqi	1	0.25%
Jordanian	3	0.76%
Lebanese	5	1.27%
Moroccan	1	0.25%
Palestinian	4	1.02%
Sudanese	1	0.25%
Syrian	2	0.51%
Yemeni	30	7.6%
Other nationality	3	0.76%
Q4. City
Riyadh	260	65.99%
Jeddah	97	24.62%
Dammam	9	2.28%
Abroad	8	2.03%
Other city	20	5.08%
Q5. Education Level
Below High School	2	0.51%
High School	50	12.69%
Bachelor’s degree	241	61.17%
Master’s degree	65	16.5%
Ph.D.	12	3.05%
Other	24	6.09%
Q6. Marital Status
Married	181	45.94%
Single	206	52.28%
Other	7	1.78%
Q7. Employment Status
Private sector employee	136	34.52%
Government sector employee	55	13.96%
Unemployed	53	13.45%
Student	113	28.68%
Retired	20	5.08%
Other	17	4.31%

displays a comprehensive breakdown of response numbers and percentages for each question.

The lighting criteria preferences were systematically classified into five distinct levels, each denoting a different level of intensity. Level 1 represented the lowest intensity, whereas Level 5 corresponded to the highest intensity. Analysis of the results revealed that the majority of respondents (36.8%) expressed a preference for Level 5 intensity lighting, closely followed by Level 4 (29.5%), Level 3 (22%), Level 2 (10.4%), and Level 1 (1.3%). These results indicate a clear inclination towards higher-intensity lighting among the participants.

In terms of CCT, a significant majority of respondents (61.8%) exhibited a preference for warm lighting. Conversely, natural daylight and cool lighting received lower preference ratings, with 27.8% and 10.4% of respondents favoring them, respectively.

Table 4. Lighting criteria preferences.

No. Preferred CCT	Level 1 1.27%	Level 2 10.41%	Level 3 22.1%	Level 4 29.4%	Level 5 36.8%
	5	41	87	116	145
Warm	5	23	46	53	89
Neutral	0	17	36	59	40
Cool	0	1	5	4	15

effectively presents the distribution of preferences across the various lighting criteria, providing valuable insights into the respondents’ lighting preferences.

The questionnaire employed in this study focused on two key aspects of lighting: illuminance and CCT. These factors were specifically chosen to address the research questions at hand. The first question, discussed in the third chapter, sought to explore the impact of texture and color on lighting intensity for mud heritage buildings. By examining the on-site experiments and questionnaire responses, it became evident that both color and texture significantly influenced the preferred illuminance. Participants expressed a strong preference for higher illuminance to accentuate the exterior mud wall texture and highlight its color. As the intensity increased, so did the preference for it.

The third research question aimed to compare the responses from the questionnaire with the existing lighting design in the case study. The results indicated that a majority of participants favored a higher illuminance, specifically opting for Level 5, which is two levels higher than the current lighting at Level 3. Interestingly, both the group that selected the current lighting intensity and the group that preferred the higher intensity shared the same CCT preference, aligning with the warm CCT present at the site. Thus, it can be concluded that while the on-site lighting intensity did not align with the preferred intensity, the CCT did.

Furthermore, variations were observed in the lighting preferences of employees from the private and government sectors. Specifically, individuals from the private sector showed a greater inclination towards higher illuminance compared to those in the government sector. This discrepancy may be attributed to generational differences, as younger individuals tend to gravitate towards private sector employment, while older generations are more prevalent in government positions. Additionally, it was noted that younger generations exhibited a preference for a choice between natural daylight and warm light, whereas older generations strongly favored natural daylight, particularly at moderate intensity levels.

Moreover, participants’ CCT preferences were found to vary with the intensity of the light. In low light conditions, the majority leaned towards a preference for natural CCT, whereas in higher intensity levels, a preference for warm CCT emerged. However, cool light was consistently the least preferred CCT among the three options presented.

These findings shed light on the intricate relationship between lighting preferences, age groups, employment sectors, and lighting conditions, providing valuable insights for future lighting design considerations.

Upon examining the results of participants’ education levels, it was found that the majority held Bachelor’s degrees. Additionally, half of the participants fell within the 20–29 age range and were either employed in the private sector or still pursuing their education. Notably, a significant majority of participants expressed a preference for higher illuminance levels, specifically Levels 3, 4, and 5, with only slight variations ranging from 4% to 6%. Level 5 garnered the highest preference percentage, while Level 3 received the lowest. Across all illuminance levels, the warm temperature was either preferred or held equal favorability to natural daylight, but it was never considered less preferred.

Furthermore, the survey results revealed that a majority of participants from Saudi Arabia and other countries favored a higher illuminance level (Level 5) and warm CCT. However, the preferences of Saudi Arabian participants showed a closer distribution among the top three levels. Conversely, participants from other countries overwhelmingly preferred Level 5. It is important to note that the number of non-Saudi participants was significantly lower than that of Saudi participants, warranting further investigation to establish a definitive conclusion. Nevertheless, it is worth highlighting that participants of non-Arab nationalities did not select the lower illuminance levels (Level 1, Level 2, and Level 3).

In short, the analysis demonstrated that color and texture significantly influenced the preferred illuminance, with higher intensities being favored to showcase the exterior mud wall texture and color. Participants generally expressed a preference for higher illuminance than the existing lighting design. However, both groups, those favoring the existing lighting and those preferring higher intensity, shared the same preference for warm CCT. Therefore, it can be concluded that the research hypothesis accurately aligns with the findings, as the illuminance employed in the case study (Prince Saad Bin Saud Palace) does not correspond to the preferred intensity indicated in the questionnaire results.

Overall, these questionnaire findings provide valuable insights for lighting design and emphasize the importance of considering color, texture, and the preferences of different demographic groups when determining illuminance and temperature. Additionally, the analysis of participant characteristics enhances the interpretation and generalizability of the findings, contributing to a better understanding of the surveyed population. This knowledge can assist designers and practitioners in making informed decisions about illuminance and CCT, ultimately creating visually comfortable environments that cater to users’ needs.

7. Discussion & Limitations

This research contributes to the field of lighting design in mud heritage buildings by establishing criteria for and providing insights into visitor preferences. It emphasizes the importance of considering cultural, aesthetic, and functional aspects in lighting design, promoting sustainable practices, and creating memorable visitor experiences.

This research yielded significant findings throughout its various stages. In the initial stages, the lighting in the At-Turaif historic district was observed to have a warm color temperature, luminaires with LED technology were the predominant luminaires used throughout the district, the main elevation of the buildings exhibited a illuminance of 320 lx, and the color of the mud surfaces was determined to have an RGB value of R: 203, G: 187, B: 149, with a glossiness of 1%.

During the third and fourth stages of this research, collecting preferences for lighting criteria through a questionnaire and analysis, the following key findings were obtained:

• Lighting in the At-Turaif historic district was observed to have a warm color temperature.
• Luminaires with LED technology were the predominant luminaires used throughout the district.
• The main elevation of the buildings exhibited an illuminance of 320 lx.
• The color of the mud surfaces was determined to have an RGB value of R: 203, G: 187, B: 149, with a glossiness of 1%.

Testing lighting criteria preferences through the questionnaire revealed a noticeable increase in preference for illuminance, with approximately 60% preference observed at 320 lx. All participant groups expressed a preference for higher illuminance, with the warm CCT being the most preferred. The cool CCT was the least preferred, suggesting a potential mismatch between cool lighting and these buildings’ desired aesthetics and cultural contexts. A neutral temperature was mostly preferred in mid-illuminance levels, emphasizing the value of mimicking the qualities of natural light for a more authentic and pleasant visual experience. Preferences among older age groups exhibited a range between warm and natural daylight temperatures, suggesting a nuanced approach to lighting design that considers individual preferences and accommodates varying lighting levels. Minor preference variations were found among different age groups, but the results were consistent overall.

The implications of the research findings can be outlined as follows:

• Preservation of Cultural Heritage: Mud heritage buildings have significant historical and cultural value, so lighting criteria are established to preserve and conserve them. The guidelines ensure that the lighting design respects the authenticity and cultural identity of the buildings, benefiting the current generation and transmitting cultural heritage to future generations.
• Enhanced Visitor Experience: Lighting is essential for visitor comfort, safety, and appreciation of architectural details. This study identifies preferences for illuminance and temperature to create lighting environments that optimize the visitor experience, making it more engaging, immersive, and memorable. This contributes to the overall enjoyment and appreciation of cultural heritage.
• Sustainability and Energy Efficiency: Research findings have implications for sustainability and energy efficiency in lighting design. Warm CCTs align with energy-efficient lighting technologies, offering visual appeal and energy savings. By incorporating these findings into lighting design practices, it is possible to create sustainable and energy-efficient lighting solutions for mud heritage buildings.
• Guidelines for Designers and Architects: This research aims to establish lighting criteria that can serve as practical guidelines for future designers and architects. It fills a gap in the existing literature by providing a comprehensive framework for lighting design in mud heritage buildings, promoting consistent and informed design decisions, and leading to better outcomes in terms of aesthetics, functionality, and cultural sensitivity.
• Transferability and Generalizability: This research focused on the At-Turaif district, but the findings can be applied to other mud heritage buildings and historical sites worldwide. This transferability and generalizability make the findings valuable for a broader range of architectural and cultural contexts, providing a foundation for lighting design that respects historical and cultural values.

Although efforts were made to reduce the impact of limitations, this manuscript still has some shortcomings that could only be avoided partially despite following the procedure outlined. One of the main limitations is the selected case study. Only one type of mud commonly used in the Kingdom Middle Region was considered. It is important to recognize that the characteristics of mud, including texture and color, can vary depending on the region of origin. Therefore, the findings of this study may not be directly applicable to other mud heritage buildings with different mud compositions.

Additionally, the duration of the study was confined to eight months, which may have restricted the scope and depth of the research. A more extensive investigation over a longer timeframe could yield further insights and enhance the generalizability of the findings.

Furthermore, the study was limited to examining only one type of lighting, thereby constraining participants’ choices and potentially influencing their preferences. This research would benefit from future studies that explore lighting preferences across a broader range of lighting types to capture the full spectrum of possibilities.

8. Recommendations & Future Research

The following recommendations are aimed to guide lighting design decisions, considering the visitors’ preferences and the specific factors highlighted in the analysis of the results:

• Consider higher illuminance levels to accentuate the exterior mud wall texture and showcase its color, as it emerged as the preferred option among participants. By incorporating higher light intensities, the unique characteristics of the mud surfaces can be more prominently highlighted.
• Recognize the significance of color and texture as influential factors in lighting design, particularly in relation to preferences for illuminance. Designing lighting solutions that effectively emphasize and enhance these aspects will contribute to a more immersive and aesthetically pleasing visitor experience.
• Ensure that the selected CCT aligns with users’ preferences before finalizing the lighting design for any project. Understanding and incorporating preferred CCTs will help harmonize visually comfortable atmospheres with users’ expectations.
• Emphasize the importance of considering the preferences of different demographic groups when determining illuminance and temperature, as this will enable the creation of visually comfortable environments that cater to the specific needs and expectations of diverse user groups.

It is recommended to conduct further research to investigate the particular factors and preferences that give rise to the differences found among various demographic groups. Additionally, incorporating other factors such as energy efficiency, cost-effectiveness, and environmental sustainability in lighting design decisions is essential for creating optimal lighting solutions that align with broader societal and ecological goals. This will deepen our comprehension of the subtle dynamics that affect lighting preferences in heterogeneous communities and enable more tailored lighting solutions.

9. Summary & Conclusions

This study sheds light on the effect of artificial lighting on both the aesthetic qualities and practical features of traditional mud buildings by thoroughly investigating sightseer behavior and preferences in the ancient At-Turaif district. This research aims to provide important insights that can direct the creation of effective lighting strategies, ensuring a harmonious integration of artificial lighting within the historical context while preserving the distinctive charm and cultural heritage of these architectural treasures.

The study’s objectives were to determine artificial lighting criteria for traditional mud buildings, examine the impact of exterior mud surfaces on these criteria, and measure preferences through a questionnaire and 3D model. The research employed a mixed methods framework to explore artificial lighting in mud heritage buildings, focusing on the At-Turaif district. Through analyzing the case study, constructing a 3D model, and testing lighting criteria preferences via a questionnaire, the research established preliminary guidelines and provided valuable insights into the impact of lighting on aesthetic values and functional aspects.

The findings of the research have several implications for the field of lighting design and preservation of mud heritage buildings. Firstly, the established lighting criteria specific to mud buildings fill a critical gap in the existing literature, providing much-needed guidelines for future designers and architects working with similar structures. Secondly, the preference for warm CCT among participants emphasizes the importance of aligning artificial lighting with the historical and cultural context of the At-Turaif district. Finally, all participant groups’ preference for higher illuminance underscores the need for adequate illumination in historical sites and mud heritage buildings to ensure visitor comfort, safety, and the visibility of architectural details. The implications of this research extend beyond the specific case study of the At-Turaif district, as it can serve as a foundation for lighting design in other mud heritage buildings and historical sites worldwide.

However, lighting preferences can be subjective and influenced by various factors, such as personal preference, cultural background, and the purpose of the space. Further research may be needed with a more extensive and diverse sample to obtain a more comprehensive understanding of lighting preferences in the population of interest. Additionally, considering other factors such as energy efficiency, cost-effectiveness, and environmental sustainability in lighting design decisions is important for creating optimal lighting solutions.