Advanced multichannel lighting control systems in heritage environments: case study of the Cathedral of Seville

Citation: Aguilar, H.; Acosta, I.; Mohamed, S.; Navarro, J. Advanced Multichannel Lighting Control Systems in Heritage Environments: Case Study of the Cathedral of Seville. Appl. Sci. 2024,14, 8242. https://doi.org/ 10.3390/app14188242 Academic Editor: Juan P. Torreglosa Received: 26 July 2024 Revised: 4 September 2024 Accepted: 10 September 2024 Published: 12 September 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). applied sciences Article Advanced Multichannel Lighting Control Systems in Heritage Environments: Case Study of the Cathedral of Seville Honorio Aguilar, Ignacio Acosta * , Sara Mohamed and Jaime Navarro Instituto Universitario de Arquitectura y Ciencias de la Construcción, Universidad de Sevilla, 41012 Seville, Spain; [email protected] (H.A.); [email protected] (S.M.); jnavarr[email protected] (J.N.) *Correspondence: [email protected]; Tel.: +34-954559517 Featured Application: The multichannel luminaire systems allow a perfect color rendering of art pieces, while preserving them against light photodegradation. The presented lighting system can be applied in architectural heritage and museums. Abstract: The appropriate preservation and color rendering of paintings and art pieces are a pending subject in architectural heritage, since, in most of the cases, lighting systems are not really focused on the conservation and suitable perception of these heritage resources, due to the limitations of standard LED lamps and lighting configurations. In this context, a multichannel luminaire system is proposed in the case study of the Cathedral of Seville, providing a variable and rich spectral distribution, which allows an excellent color perception linked to the daylight conditions, while the short-wavelength light is minimized in order to reduce photodegradation. Two scenarios are addressed: Museum of the Cathedral and Evangelist Chapel. The multichannel luminaire system is tested by means of subjective surveys and objective procedures (Farnswoth-Munsell and Natural Color System tests). The results show that the proposed spectral distribution of the multichannel system provides a better color discrimination in comparison with typical lighting systems, as well as a better preservation, defining a suitable lighting technology for architectural heritage. The novelty of this study lies in the multi-parameter approach, taking care of color rendering while photodegradation is minimized. Keywords: multichannel luminaire; light spectra; daylight; electric lighting; color rendering; colorimetry; photodegradation 1. Introduction and Objectives 1.1. Background Currently, advancements in lighting technology are markedly enhancing the energy efficiency promoted by LED light sources, with a primary focus on reducing energy consumption and corresponding CO2emissions [1]. Nonetheless, this progression frequently overlooks the implications of this type of luminaires on color appreciation [ 2 ], human health effect [ 3 , 4 ], and well-being [ 5 ]. As posited by various researchers, lighting design in architecture should encompass considerations beyond the mere distribution and quantity and light, extending to its quality [ 6 – 8 ], thereby fostering a comfortable scenario for users and a proper perception of the environment. Most of the lighting systems currently available on the market employ LED technology, which generates a distinct spectral distribution compared to older sodium-vapor, halogen, and fluorescent lamps, resulting in a noticeable variation in color fidelity and chromaticity. Specifically, LED lamps exhibit significant variation in their chromatic perception due to the peak located in the short-wavelength spectrum [ 9 ]. LED lamps are cost-effective and provides a higher luminous efficacy in comparison with their predecessors. In addition to the previous observations, the cutting-edge technology of LED lamps offers an interesting solution for improving color perception in architectural environments: Appl. Sci. 2024,14, 8242. https://doi.org/10.3390/app14188242 https://www.mdpi.com/journal/applsci Appl. Sci. 2024,14, 8242 2 of 17 multichannel luminaires. This type of light source, usually controlled by a DALI language, adapts the spectral power distribution (SPD) of the lamp, with the aim to render, in an optimized way, the colors of unique spaces of architectural heritage. The multichannel luminaire, composed of a set of LED lamps with different peaks and bandwidths in the visible range, can mimic the spectral distribution of daylight with noticeable accuracy, thus improving the light quality and the object’s appearance [10]. Given this context, the lighting design of museums, churches, and similar heritage buildings acquire a new tool for improving the color perception of inner spaces, creating unique atmospheres depending on the designer’s intention [ 11 ]. Accordingly, by modifying the Correlated Color Temperature (CCT), which can be deduced from the SPD of the light source, the chromaticity of the different hues of paintings can be adapted to different scenarios, changing, therefore, the observer’s perception [ 12 ]. As an example, multichannel luminaires can render the spectral distribution of a real flame, with the aim to reproduce paintings and frescoes as ancestral observers saw such elements [ 13 ], opening a wide range of potential solutions with this new technology. The scenario described underscores the necessity for a precise evaluation of the effects induced by these new lamps on color rendering [ 14 ], since, as described above, this technology is currently used in heritage environments, where the hue fidelity and chromaticity discrimination are crucial for a suitable understanding of paintings, frescoes, and altar pieces. There are several procedures to define the color rendering provided by a light source from a quantitative approach. One of the latest and more widespread methods for fully describing the color perception is TM-30-20, defined by the Illuminating Engineering Society of North America (IESNA) [ 15 ]. This procedure contrasts, in the CIE Lab color space, the results for 99 hue samples, setting a continuous illuminant reference which is adapted depending on the CCT of the studied light source. IESNA is currently advocating for the adoption of this method among lighting manufacturers [ 16 ]. Moreover, the Daylight Spectrum Index (DSI) [ 17 ] is a novel concept which offers a different approach for defining the color preference, using SPD fitting instead of the analysis of hue sample deviation within a color space. This innovative concept assesses the color similarity provided by a lamp in comparison with daylight, contrasting the SPD of both sources, depending on the color sensitivity functions of human vision. Thus, the goal of this concept is to determine how closely the color perception produced by a light source matches that of daylight, considering natural light as the perfect reference for color rendering. Moreover, color rendering is not the sole variable to take into account in lighting design. The chromatic preference can vary depending on the studied scenario, and thus color rendering can be influenced by boundary conditions, such as the color of the walls and ceiling, the geometry of the inner space, or the task developed by the observer [ 18 ]. In line with this assertion, Schanda et al. [ 19 ] evaluated color fidelity in the case study of a picture gallery, selecting multichannel LED luminaires for this specific application. Bellia et al. [ 20 ] carried out an interesting study which modified not only the flux and CCT of light sources, but also the wall color of a simulated picture gallery. The results showed that a combination of the three parameters affect the color perception of the observers. Moreover, Zhai et al. [ 21 ] also studied the effect of CCT in the color perception of fine art paintings, determining that low CCT values (near 3500 K) are suitable for hue discrimination. In a different setting, Szabóet al. [ 22 ] examined color preference for a retail shop, determining the appropriate SPD for LED luminaires. More recently, Lin et al. [ 2 ] analyzed color preference across various scenarios, including retail displays, supermarkets, and restaurants, with each case study yielding distinct results. Notably, research by Royer et al. [ 23 ] evaluated color preference with 25 participants, concluding that most of the color rendering metrics do not align with color preference criteria, despite the fact that these preferences can be predicted using calculation models based on the metrics defined by TM-30-20, namely the Gamut Index (Rg) and the Fidelity Index (Rf). Appl. Sci. 2024,14, 8242 3 of 17 The picture that emerges from the described scenario led us to conclude that the most effective way to determine the color perception—given both objective and subjective parameters—is through surveys to determine the hue preference of the observer for a specific venue, as well as objective trials, such as the Farnsworth-Munsell (FM-100) or the Natural Color System tests, as evidenced by the following studies: Houser et al. [ 24 ] conducted comprehensive research, analyzing 40 surveys to assess whiteness perception considering various LED lamps, concluding that blue wavelength light is needed to induce whiteness. Moreover, Jost-Boissard et al. [ 25 ] assessed the color quality provided by LED lamps, examining a wide range of light sources with different CCT across more than 80 surveys. Similarly, Dangol et al. [ 26 ] analyzed the precision of different color metrics using 20 surveys with different LED lamps, according to different CCTs. A recent example is the study by Gu et al. [ 27 ], which studied a set of color rendering metrics using 10 surveys, concluding that the CAM02-UCS color space is suitable for determining hue deviation. It must be noted that the performing of color tests depends on many parameters, such as the color of the environment and the age of the participants. When developing tests to determine a light source’s ability to differentiate colors, it is crucial that the tests provide an objective quantification of the results [ 28 ]. Esposito et al. [ 29 ] defined a new procedure for measuring the color discrimination, Rd, which assigns a score based on the number of transpositions made in the FM-100 trial. An Rd close to zero indicates an excellent color discrimination, while a score greater than 16 indicates poor hue discrimination. As can be deduced from the above, color rendering concepts are continually evolving due to the lack of solid criteria for determining a light source’s chromatic performance [ 30 ]. Moreover, most metrics focus on quantifying color deviation, neglecting the need to distinguish colors with similar hues, brightness, and chromaticity. Therefore, one of the most appropriate procedures for defining the lighting quality is the performance of objectivequantitative surveys, which can serve to determine the suitability of a lighting design in special sensitivity heritage spaces, where a careful and adequate design can improve or highlight the perception of the environment. Finally, it must be noted that the radiation from any light source generates visual photodegradation of paintings, pictures, and other art pieces [ 31 ]. The damage produced in color perception depends on the spectrum of the source (particularly the short-wavelength radiation, which affects yellow and red hues), the illuminance (with a recommended average value between 50 and 100 lx), the exposure time, and the chemical composition of the color pigments. Several researchers in this field, such as Durmus et al. [ 32 ], have studied the appropriate spectral distribution of multichannel LED luminaires with the aim of preserving and reducing visual photodegradation and hue shifts in paintings. Therefore, the balance between color perception and the preservation of art piece is crucial in sensitive heritage spaces. 1.2. Aim and Objectives According to the needs and opportunities described in the background, a new study is proposed, with the aim to determine the appropriate multichannel LED lighting system to achieve an optimized solution of color rendering in the case study of the Cathedral of Seville, providing a variable and rich spectral distribution, which allows an excellent color perception linked to the daylight conditions, while the short-wavelength light is minimized in order to reduce photodegradation. Two scenarios are addressed: Museum of the Cathedral, where there is a clear influence of daylight coming from the adjacent courtyard, and Evangelist Chapel, decorated with large paintings in a golden altar piece. The multichannel luminaire system is tested by means of subjective surveys and objective procedures (Farnswoth-Munsell and Natural Color System tests). The subjective surveys were performed in the settings of the aforementioned case studies, while the objective trials were carried out in the controlled scenario of a Light Lab. The color rendering of the multichannel luminaires is compared with other luminaires types and Appl. Sci. 2024,14, 8242 4 of 17 light sources, such as halogen or standard LED lamps, as well as the simulated spectrum of daylight, in order to determine, in a comparative way, the benefits promoted by the proposed lighting system. Finally, the selected multichannel spectrum is analyzed with the aim to determine the potential photodegradation according to the CIE procedures [ 31 ], therefore preserving the art pieces and paintings of both case studies. 2. Materials and Methods 2.1. Multichannel Luminaire System Description The multichannel luminaires used in both the Cathedral case studies and the Light Lab are Ledmotive VEGA 07 luminaires. These luminaires were selected for their capability to render a broad set of SPDs. This is achieved through the use of seven light channels, each with a sufficient radiometric output and a narrow wavelength range per channel. Additionally, this type of lamp can be adapted for use in spotlight luminaires, which emit a narrow intensity distribution, making them particularly suitable for applications in museums and churches. Therefore, the luminous output is produced by mixing seven wavelength colors, with each spectrum determined by seven independent PWM signals. Each channel communicates with the driver via the RS-485 protocol, commonly used in serial communication systems. The emission range of this luminaire spans from 420 to 730 nm, covering most of the visible range of human perception, as can be deduced from Figure 1. Appl. Sci. 2024, 14, x FOR PEER REVIEW 4 of 17 The multichannel luminaire system is tested by means of subjective surveys and objective procedures (Farnswoth-Munsell and Natural Color System tests). The subjective surveys were performed in the settings of the aforementioned case studies, while the objective trials were carried out in the controlled scenario of a Light Lab. The color rendering of the multichannel luminaires is compared with other luminaires types and light sources, such as halogen or standard LED lamps, as well as the simulated spectrum of daylight, in order to determine, in a comparative way, the benefits promoted by the proposed lighting system. Finally, the selected multichannel spectrum is analyzed with the aim to determine the potential photodegradation according to the CIE procedures [31], therefore preserving the art pieces and paintings of both case studies. 2. Materials and Methods 2.1. Multichannel Luminaire System Description The multichannel luminaires used in both the Cathedral case studies and the Light Lab are Ledmotive VEGA 07 luminaires. These luminaires were selected for their capability to render a broad set of SPDs. This is achieved through the use of seven light channels, each with a sufficient radiometric output and a narrow wavelength range per channel. Additionally, this type of lamp can be adapted for use in spotlight luminaires, which emit a narrow intensity distribution, making them particularly suitable for applications in museums and churches. Therefore, the luminous output is produced by mixing seven wavelength colors, with each spectrum determined by seven independent PWM signals. Each channel communicates with the driver via the RS-485 protocol, commonly used in serial communication systems. The emission range of this luminaire spans from 420 to 730 nm, covering most of the visible range of human perception, as can be deduced from Figure 1. Figure 1. Multichannel luminaire spectral information. (A) Peak emission and Full Width at Half Maximum (FWHM) per channel. (B) CIE 1931 Chromatic Diagram, rendering the seven channels positions and the black body curve. (C) Spectral Power Distribution (SPD) per channel. (http://www.ledmotive.com/ accessed on 19 March 2023). Figure 1. Multichannel luminaire spectral information. (A) Peak emission and Full Width at Half Maximum (FWHM) per channel. (B) CIE 1931 Chromatic Diagram, rendering the seven channels positions and the black body curve. (C) Spectral Power Distribution (SPD) per channel. (http://www. ledmotive.com/ accessed on 19 March 2023). With all channels set to their maximum level, the luminaire consumes 80 W of power and emits a luminous flux of 4460 lm. As can be deduced, the luminous efficiency is lower than that of a standard LED because this set of lamps is designed to achieve optimal color rendering rather than energy efficiency. Appl. Sci. 2024,14, 8242 5 of 17 The photometry of the luminaire is similar to a Lambertian distribution for the luminaire used in the Light Lab, as shown in Figure 2, matching that of a typical medium-sized downlight. This luminaire model was also used in the showcases of the Museum of the Cathedral, where silver and gold art pieces are exhibited. Additionally, the paintings in the Museum and the Evangelist Chapel are illuminated by medium-distance spotlights equipped with reflectors to narrow the emission cone, focusing the light on the art pieces. Appl. Sci. 2024, 14, x FOR PEER REVIEW 5 of 17 With all channels set to their maximum level, the luminaire consumes 80 W of power and emits a luminous flux of 4460 lm. As can be deduced, the luminous efficiency is lower than that of a standard LED because this set of lamps is designed to achieve optimal color rendering rather than energy efficiency. The photometry of the luminaire is similar to a Lambertian distribution for the luminaire used in the Light Lab, as shown in Figure 2, matching that of a typical medium-sized downlight. This luminaire model was also used in the showcases of the Museum of the Cathedral, where silver and gold art pieces are exhibited. Additionally, the paintings in the Museum and the Evangelist Chapel are illuminated by medium-distance spotlights equipped with reflectors to narrow the emission cone, focusing the light on the art pieces. Figure 2. (A) Photometry distribution of the VEGA 07 downlight. (B) Interface of the control logic. The flexibility and adaptation of the multichannel luminaires allow the rendering of different SPDs, emulating a collection of spectral distributions that permits the comparison of the proposed spectrum with those corresponding to the typical light sources used in heritage environments. Accordingly, a multichannel spectrum is proposed to optimize color discrimination and fidelity, while minimizing the photodegradation of the art pieces. This selected spectrum is compared with other typical light sources, such as standard LED lamps (both warm and cool sources, corresponding to CCTs of 2700 and 5500 K), incandescent lamp (similar to the Standard Illuminant A), and daylight (rendering a sunny sky with a CCT of 5000 K and a standard or overcast sky with a CCT of 6500 K). Figure 3 represents the spectral distribution of the selected light sources. The selected SPDs exhibit a Fidelity Index (Rf) and a Gamut Index (Rg) both exceeding 90, indicating that accurate color perception can be expected across all studied scenarios. The multichannel LED optimized spectrum has been selected according to the following conditions: 1. The simulated color rendering, defined by TM-30-20 procedure [15], must be higher than 90. The proposed SPD achieves a Fidelity Index (Rf) of 90 and a Gamut Index (Rg) of 95, providing excellent performance in color fidelity and discrimination. 2. The entire visible spectrum must be covered by the SPD emission of the luminaire to provide similar chromaticity to most hues in the visible range. 3. The visible photodegradation must be lower than the case of cool LED lamps, according to the CIE 157:2004 procedure [31]. Figure 4 shows the results of the visible damage of the proposed multichannel luminaire and the critical exposure duration in Figure 2. (A) Photometry distribution of the VEGA 07 downlight. (B) Interface of the control logic. The flexibility and adaptation of the multichannel luminaires allow the rendering of different SPDs, emulating a collection of spectral distributions that permits the comparison of the proposed spectrum with those corresponding to the typical light sources used in heritage environments. Accordingly, a multichannel spectrum is proposed to optimize color discrimination and fidelity, while minimizing the photodegradation of the art pieces. This selected spectrum is compared with other typical light sources, such as standard LED lamps (both warm and cool sources, corresponding to CCTs of 2700 and 5500 K), incandescent lamp (similar to the Standard Illuminant A), and daylight (rendering a sunny sky with a CCT of 5000 K and a standard or overcast sky with a CCT of 6500 K). Figure 3represents the spectral distribution of the selected light sources. The selected SPDs exhibit a Fidelity Index (Rf) and a Gamut Index (Rg) both exceeding 90, indicating that accurate color perception can be expected across all studied scenarios. The multichannel LED optimized spectrum has been selected according to the following conditions: 1. The simulated color rendering, defined by TM-30-20 procedure [ 15 ], must be higher than 90. The proposed SPD achieves a Fidelity Index (Rf) of 90 and a Gamut Index (Rg) of 95, providing excellent performance in color fidelity and discrimination. 2. The entire visible spectrum must be covered by the SPD emission of the luminaire to provide similar chromaticity to most hues in the visible range. 3. The visible photodegradation must be lower than the case of cool LED lamps, according to the CIE 157:2004 procedure [ 31 ]. Figure 4shows the results of the visible damage of the proposed multichannel luminaire and the critical exposure duration in hours before perceptible visual damage occurs, considering an average illuminance of 100 lx from 8:00 am to 8:00 pm with a protective glass. Appl. Sci. 2024,14, 8242 6 of 17 Appl. Sci. 2024, 14, x FOR PEER REVIEW 6 of 17 hours before perceptible visual damage occurs, considering an average illuminance of 100 lx from 8:00 am to 8:00 pm with a protective glass. Figure 3. Spectral Power Distributions of the selected light sources, indicating the emulated light with the multichannel luminaire and the real spectrum. Figure 4. (A) SPD of the multichannel luminaire, protective glass transmittance and relative spectral sensitivity functions for different exposures materials. (B) Critical exposure duration for multichannel and standard LED luminaires, measured in hours. 2.2. Case Studies The multichannel LED system was installed in the Museum of the Cathedral of Seville and the Evangelist Chapel. Both sites were recently restored, ensuring that the artworks were in an acceptable state of preservation throughout the study process. The selection of these case studies is based on the divergent lighting conditions of both scenarios. In the museum, the lighting is significantly influenced by the adjacent courtyard, Patio del Figure 3. Spectral Power Distributions of the selected light sources, indicating the emulated light with the multichannel luminaire and the real spectrum. Appl. Sci. 2024, 14, x FOR PEER REVIEW 6 of 17 hours before perceptible visual damage occurs, considering an average illuminance of 100 lx from 8:00 am to 8:00 pm with a protective glass. Figure 3. Spectral Power Distributions of the selected light sources, indicating the emulated light with the multichannel luminaire and the real spectrum. Figure 4. (A) SPD of the multichannel luminaire, protective glass transmittance and relative spectral sensitivity functions for different exposures materials. (B) Critical exposure duration for multichannel and standard LED luminaires, measured in hours. 2.2. Case Studies The multichannel LED system was installed in the Museum of the Cathedral of Seville and the Evangelist Chapel. Both sites were recently restored, ensuring that the artworks were in an acceptable state of preservation throughout the study process. The selection of these case studies is based on the divergent lighting conditions of both scenarios. In the museum, the lighting is significantly influenced by the adjacent courtyard, Patio del Figure 4. (A) SPD of the multichannel luminaire, protective glass transmittance and relative spectral sensitivity functions for different exposures materials. (B) Critical exposure duration for multichannel and standard LED luminaires, measured in hours. 2.2. Case Studies The multichannel LED system was installed in the Museum of the Cathedral of Seville and the Evangelist Chapel. Both sites were recently restored, ensuring that the artworks were in an acceptable state of preservation throughout the study process. The selection of these case studies is based on the divergent lighting conditions of both scenarios. In the museum, the lighting is significantly influenced by the adjacent courtyard, Patio del Limonar. Therefore, the spectral distribution and resulting CCT of the electric lighting must account for daylight influence. To address this, the SPD of the multichannel system Appl. Sci. 2024,14, 8242 7 of 17 is adapted to the daylight spectrum, imitating the color temperature of the natural light source to avoid distorting the hues of the ambient light. Conversely, the Evangelist Chapel lacks natural light influence, so the design focuses on suitable illumination of the paintings and proper color rendering of the altar piece, ensuring both hue discrimination and an adequate balance of chromaticity. An initial setup was conducted in the Museum to determine the optimal placement of the spotlights, avoiding specular reflections on the varnish of the paintings from the observer’s position, as shown in Figure 5B. The goal was to cover the entire surface of the painting, optimizing horizontal illuminance uniformity. After the spotlight installation, the SPDs of the multichannel luminaires adapt their CCT according to daylight conditions, as shown in Figure 6. The natural light spectrum from the courtyard is inferred from an outdoor webcam that translates the sky color to a specific CCT, which is then interpreted by the light driver to assign a corresponding SPD to the electric luminaires. Appl. Sci. 2024, 14, x FOR PEER REVIEW 7 of 17 Limonar. Therefore, the spectral distribution and resulting CCT of the electric lighting must account for daylight influence. To address this, the SPD of the multichannel system is adapted to the daylight spectrum, imitating the color temperature of the natural light source to avoid distorting the hues of the ambient light. Conversely, the Evangelist Chapel lacks natural light influence, so the design focuses on suitable illumination of the paintings and proper color rendering of the altar piece, ensuring both hue discrimination and an adequate balance of chromaticity. An initial setup was conducted in the Museum to determine the optimal placement of the spotlights, avoiding specular reflections on the varnish of the paintings from the observer’s position, as shown in Figure 5B. The goal was to cover the entire surface of the painting, optimizing horizontal illuminance uniformity. After the spotlight installation, the SPDs of the multichannel luminaires adapt their CCT according to daylight conditions, as shown in Figure 6. The natural light spectrum from the courtyard is inferred from an outdoor webcam that translates the sky color to a specific CCT, which is then interpreted by the light driver to assign a corresponding SPD to the electric luminaires. Figure 5. From left to right and from top to bottom: (A) Installation of the multichannel spotlights in front of the Evangelist Chapel. (B) Initial set-up of the lighting system in the Cathedral Museum. (C) Spectral configuration of the multichannel system in the Evangelist Chapel. The installation of the luminaires in the Evangelist Chapel involved placing spotlights on two rail systems located in front of the altar piece, as shown in Figure 5A. Next, the spectral configuration of the luminaires was adjusted, as can be inferred from Figure 5C, to find the suitable SPD for achieving optimized color fidelity and hue discrimination. The final results, showcasing different CCT configurations, can be seen in Figure 7. Figure 5. From left to right and from top to bottom: (A) Installation of the multichannel spotlights in front of the Evangelist Chapel. (B) Initial set-up of the lighting system in the Cathedral Museum. (C) Spectral configuration of the multichannel system in the Evangelist Chapel. The installation of the luminaires in the Evangelist Chapel involved placing spotlights on two rail systems located in front of the altar piece, as shown in Figure 5A. Next, the spectral configuration of the luminaires was adjusted, as can be inferred from Figure 5C, to find the suitable SPD for achieving optimized color fidelity and hue discrimination. The final results, showcasing different CCT configurations, can be seen in Figure 7. Appl. Sci. 2024,14, 8242 8 of 17 Appl. Sci. 2024, 14, x FOR PEER REVIEW 8 of 17 Figure 6. Adaptation of the multichannel lighting system in the case study of a painting in the Cathedral Museum, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65. Figure 7. Adaptation of the multichannel lighting system in the case study of the Evangelist Chapel, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65 (image taken from a global point of view, not from the observer’s position). Figure 6. Adaptation of the multichannel lighting system in the case study of a painting in the Cathedral Museum, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65. Appl. Sci. 2024, 14, x FOR PEER REVIEW 8 of 17 Figure 6. Adaptation of the multichannel lighting system in the case study of a painting in the Cathedral Museum, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65. Figure 7. Adaptation of the multichannel lighting system in the case study of the Evangelist Chapel, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65 (image taken from a global point of view, not from the observer’s position). Figure 7. Adaptation of the multichannel lighting system in the case study of the Evangelist Chapel, from left to right and from top to bottom: multichannel lamp, incandescent lamp, warm LED, cool LED, CIE D50, and CIE D65 (image taken from a global point of view, not from the observer’s position). Appl. Sci. 2024,14, 8242 9 of 17 The objective trials—which correspond to the Farnsworth-Munsell and Natural Color System tests—were conducted in the Light Lab at the School of Architecture, University of Seville, shown in Figure 8. This lab is equipped with nine multichannel LED luminaires, the same model used in the case studies of the Cathedral of Seville, allowing the same SPD to be reproduced in a laboratory environment. The luminaires are mounted on the ceiling with an opal diffuser that creates a Lambertian distribution of light. The lab’s walls are made of mirrors with an average reflectance of 97%, although neoprene sheets of different colors can be added to alter the scenario’s perception. Appl. Sci. 2024, 14, x FOR PEER REVIEW 9 of 17 The objective trials—which correspond to the Farnsworth-Munsell and Natural Color System tests—were conducted in the Light Lab at the School of Architecture, University of Seville, shown in Figure 8. This lab is equipped with nine multichannel LED luminaires, the same model used in the case studies of the Cathedral of Seville, allowing the same SPD to be reproduced in a laboratory environment. The luminaires are mounted on the ceiling with an opal diffuser that creates a Lambertian distribution of light. The lab’s walls are made of mirrors with an average reflectance of 97%, although neoprene sheets of different colors can be added to alter the scenario’s perception. Figure 8. Multichannel LED system installed in the Light Lab: sequence of CCT variation: 2700 K, 3000 K, 3500 K, 4000 K, 5000 K, and 6500 K. 2.3. Subjective and Objective Trials A subjective trial was conducted with 30 participants within the environments of the Cathedral’s Museum and the Evangelist Chapel case studies. The study sample comprised 11 men and 19 women, aged between 22 and 36 years. The participants in this study do not exhibit color blindness, and the selected age range was chosen to avoid corneal degradation associated with aging, which can impair the perception of short-wavelength colors. Participants completed a subjective test assessing their satisfaction with color appearance and their preferences regarding the lighting design for each simulated scenario, resulting in a total of 180 surveys. The questionnaire addressed the following issues: • What is your level of satisfaction with the color rendering? (very unsatisfied/unsatisfied/neutral/satisfied/very satisfied) • What is your level of satisfaction with the perception of colors? (very unsatisfied/unsatisfied/neutral/satisfied/very satisfied) • How do you perceive the hue of the lighting in the space? (very cool/cool/neutral/warm/very warm) The results are summarized to complement those observed in the objective trials. It should be noted that respondents’ answers may not align with the hue discrimination and color fidelity assessments conducted in the Light Lab, as psychological preferences can differ from objective color perception, as deduced from previous studies [33]. Figure 8. Multichannel LED system installed in the Light Lab: sequence of CCT variation: 2700 K, 3000 K, 3500 K, 4000 K, 5000 K, and 6500 K. 2.3. Subjective and Objective Trials A subjective trial was conducted with 30 participants within the environments of the Cathedral’s Museum and the Evangelist Chapel case studies. The study sample comprised 11 men and 19 women, aged between 22 and 36 years. The participants in this study do not exhibit color blindness, and the selected age range was chosen to avoid corneal degradation associated with aging, which can impair the perception of short-wavelength colors. Participants completed a subjective test assessing their satisfaction with color appearance and their preferences regarding the lighting design for each simulated scenario, resulting in a total of 180 surveys. The questionnaire addressed the following issues: •What is your level of satisfaction with the color rendering? (very unsatisfied/unsatisfied/neutral/satisfied/very satisfied) •What is your level of satisfaction with the perception of colors? (very unsatisfied/unsatisfied/neutral/satisfied/very satisfied) •How do you perceive the hue of the lighting in the space? (very cool/cool/neutral/warm/very warm) The results are summarized to complement those observed in the objective trials. It should be noted that respondents’ answers may not align with the hue discrimination and color fidelity assessments conducted in the Light Lab, as psychological preferences can differ from objective color perception, as deduced from previous studies [33]. Appl. Sci. 2024,14, 8242 16 of 17 also ensuring objective color fidelity and discrimination, as confirmed by the survey results. The system’s spectral power distribution (SPD) is balanced to cover most hues in the visible spectrum, minimizing visible photodegradation—according to the CIE 157:2004 procedure—and thereby preserving artworks in architectural heritage environments. Author Contributions: Conceptualization, I.A. and J.N.; methodology, I.A.; validation, H.A. and S.M.; formal analysis, I.A., H.A. and S.M.; investigation, I.A., H.A. and S.M.; resources, I.A. and J.N.; data curation, I.A.; writing—original draft preparation, I.A., H.A. and S.M.; writing—review and editing, I.A. and J.N.; visualization, I.A. and S.M.; supervision, J.N.; project administration, J.N.; funding acquisition, I.A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by “Agencia Estatal de Investigación” (AEI) and the “Ministerio de Ciencia e Innovación” (MCIN) of the Government of Spain, through the research project CHRONOLIGHT: Biodynamic wide spectrum lighting for biological chronoregulation and pathogens neutralization in hospital facilities (Ref PID2020-117563RB-I00) and by “Fundación BBVA (FBBVA), through the research project HERILED: Design of multi-channel LED lighting systems in heritage spaces to optimize color performance and minimize biodegradation of art works (Ref IN[20]_ING_ARQ_0110). Institutional Review Board Statement: Ethical review and approval were waived for this study because there is no impact on the health and well-being of the human participants. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. 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