## 2 Materials and Methods  
### 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.  
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. 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/](http://www.ledmotive.com/)]([http://www.ledmotive.com/](http://www.ledmotive.com/)) accessed on 19 March 2023). 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. 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].