## 5 Design Evaluation  
### Lighting Simulation  
The most uncomfortable aspect of the library's light environment is glare, and some of the simulations we have performed to verify the effectiveness of the designed device have been conducted from the perspective of whether it can solve the glare problem [15,16].  
Glare is a condition that causes visual discomfort and reduces the visibility of objects via inappropriate luminance distribution in the visual field [17,18]. The glare in the library under study is mainly caused by excessive luminosity outside the window. The degree of uncomfortable glare is assessed on the glare index, which indicates the contrast between a glare source (characterized by its size, luminance, and position inside the field of view) and the average luminance of the background [19,20].  
The indoor glare comfort evaluation index used in this study is Daylight Glare Probability (DGP), which is an index used for evaluating the degree of glare caused by strong solar insolation in the room and is obtained by analysing the difference in brightness in the line of sight, the orientation of light in the line of sight, and the subjective level of human comfort. Compared with older glare indicators (e.g., UGR, DGI, CGI, VCP), DGP is the most up to date index used to evaluate glare derived from daylight. The calculation formula (Figure 9) and evaluation process of DGP (Table 5) are as follows [3,21].  
For this model and simulation, the Ladybug and Honeybee platform is used in Rhino's parametric plug-in Grasshopper, a parametric lighting performance analysis plug-in group based on the Grasshopper platform [22, 23, 24]. Honeybee combines Grasshopper with other building performance analysis software, such as Radiance, Energy Plus, Daysim and Open Studio, to simulate building interior glare using specific cell sets, see Figure 10.  
Regarding the creation of the library model, since the building plan is E-shaped and the three reading rooms, A, B and C, are similar in layout, only one model (of reading room A, as shown in Figure 11) is created for simulation. In the simulation, the model is given materials and local climate data, and sky data are imported. As for the viewing angle, in our analysis, the DGP index is measured at the \"eye level\" (Figure 12) of a green mannequin sitting at a desk near the west window, with its line of sight parallel to the  
Figure 9: Evaluation formula of DGP.  
\begin{table}
\begin{tabular}{c c} \hline \hline Intelorable Glare & 0.45 \textless{} DGP \\ \hline Disturbing Glare & 0.4 \textless{} DGP \textless{} 0.45 \\ \hline Perceptible Glare & 0.35 \textless{} DGP \textless{} 0.4 \\ \hline Imperceptible Glare & DGP \textless{} 0.35 \\ \hline \hline \end{tabular}
\end{table}
Table 5: DGP evaluation level and range.  
In our simulation, based on the results of field research performed in the library reading room and data from a student questionnaire, we selected typical days at typical times, and conducted an analysis of glare data before and after the installation of the designed SUNSHADE device, so as to verify the effectiveness of this device.  
We selected the typical times of 6:00 p.m. on 20 February, 6:00 p.m. on 31 April and 5:00 p.m. on 30 December, and measured the DGP index of the A400 reading room before and after the installation of the SUNSHADE device by simulation.  
According to the results of this simulation (Figure 13), before the installation of the SUNSHADE device, the glare problem at the selected specific time was more serious, and the DGP index scores all exceeded 0.45, reaching unbearable glare levels, and even reaching a maximum value of 1 at 5:00 p.m. on 30 December. After the addition of the SUNSHADE device, the DGP index dropped significantly, with all scores less than 0.35, denoting imperceptible glare, showing that the light environment reached a more comfortable state.