## 2 Materials and Methods (Testing and Simulation Methodologies)
### Testing Campaign  
The first step in the proposed methodology was the design of the testing campaign, where it was necessary to define the scope of the research and to establish a schedule for measuring the lighting levels in the chosen classrooms. When creating the schedule, it was important to define the times of day during which the data should be collected, as these data might be greatly affected by sunlight. Thus, it was determined that the measurements should be taken in the most unfavorable case in terms of illumination, which is between sunset and sunrise (when there is less outside light and the classroom lighting reaches the minimum possible value). It should be emphasized that there is still academic activity at ETSIAE after sunset. It was also necessary to plan the manpower and time needed to properly conduct the testing campaign, as the measurements in a single classroom can take a significant amount of time (between 30 min and several hours). Finally, it should be highlighted that the measurements were taken in winter, when there are more hours of darkness for measuring, and with all window blinds lowered.  
This study includes measurements of the lighting levels on student desks and blackboards in 39 ETSIAE classrooms (see Figure 2), distributed among buildings A, B, and E. It includes all ETSIAE classrooms dedicated to traditional teaching (i.e., not multimedia classrooms). A CEM-DT 1308 lux meter and a DEXTER CM30 distance meter were used in this testing campaign (see Figure 3). In addition to the geometry of the classrooms, the arrangement of lights, desks, blackboards, and other elements that might interfere with lighting (such as platforms, cabinets, columns, pillars, beams, etc.) were precisely identified. This was done in order to reproduce both the geometry and the lighting conditions of the classrooms as accurately as possible in the subsequent simulation. Similarly, the brand and model of each light in the classrooms were also identified.  
Figure 2: Diagram of the position and distribution of the points selected for illumination measurements on the blackboards (**a**) and desks (**b**) in the classrooms.  
Once the geometry of the classrooms was determined, the illuminance values, \(E\), were measured on the surfaces of interest (blackboards, tables, and student desks). Blackboards are elements of great importance to the educational process, as students use them to take notes and to understand the professors' explanations. In fact, UNE 12464-1 gives them special importance in terms of lighting, with an average illuminance reference value of 500 lx. (This value may vary according to national regulations [20].) In order to measure the illumination distribution, it was chosen to measure points one meter apart on the average line of the blackboard (see Figure 2). These points were measured at mid-height, since direct classroom observations revealed that most of the professors' notes on the blackboard were made in this area.  
With regard to student desks, it was noted that students rarely place paper in the center of the desk to write, but tend to tilt it toward one side depending on their dominant hand. Bearing this in mind, the four corners of the desk as well as the central point were defined as measurement points. For long desks with more than one seat, the part corresponding to each seat was treated as an individual desk and the two corners in contact with each other were treated as a single point (see Figure 2).  
A significant number of measurement points was obtained in each classroom, ranging from 134 points in the smallest classroom to 2275 points in one of the examination rooms. The measurements were collected on cards such as the one shown in Figure 4. Each group of desks is identified in one color according to the level of lighting achieved (the closer the desks are to the dark red color, the poorer the lighting).  
Figure 3: Equipment used in the testing campaign: (**a**) CEM-DT 1308 lux meter, (**b**) DEXTER CM30 distance meter, and (**c**) measuring tape.