## 2 Materials and Methods
### Discuss and Suggestions on the Lighting Control of Classroom Lighting Luminaires  
To evaluate the visual clarity of projection teaching, we can measure the average luminance on screen which corresponds to clarity level, and know whether the total average luminance under each lighting control conditions is clear enough for the students, to ensure effective teaching while using slideshows. The results can be used as a reference in practice of how to control the lighting mode when using the projection screen in teaching. The overall average luminance of level 1, where the classroom luminaires are fully turned on, is 180.72 cd/m\({}^{2}\) as shown in Table 4, and when referred to the x column of Table 5, the visual clarity of the human eye perception falls between blurry (103.85 cd/m\({}^{2}\)) and the blurriest (223.45 cd/m\({}^{2}\)), a bad and unacceptable projection quality. The average luminance of level 2, with the first row luminaires off, is 90.56 cd/m\({}^{2}\), and the clarity falls between normal (48.26 cd/m\({}^{2}\)) and blurry (103.85 cd/m\({}^{2}\)). The average luminance of the level 3, the first 2 row luminaires off is 52.14 cd/m\({}^{2}\), although the clarity falls between normal and blurry as is level 2, however it is closer to normal level (48.26 cd/m\({}^{2}\)), so level 3 is within the acceptable range of clarity for human eye. The total average luminance of the level 4, all luminaires off, is 12.879 cd/m\({}^{2}\), the clarity falls between clear (22.42 cd/m\({}^{2}\)) and the clearest (10.42 cd/m\({}^{2}\)), which is the best visual clarity. Therefore, when projection screen is used in the classroom, the best lighting control mode is level 4 where all the luminaires are turned off enabling the students to better (and clearly) recognize the projection content. However, the drawback of level 4 is that the luminance contrast ratio in the classroom will be too strong causing strong and serious contrast glare, which is unfavorable and unhealthy for students' visual experience. If we adapt level 3 and have the first two row luminaires closed, we can still maintain good projection screen clarity when teaching, reducing uncomfortable contrast glare, and provide students in the desk area enough lighting to take notes and writing therefore it is a better and much more suitable lighting control mode for classrooms. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Item** & **Specification** & **Distribution** \\ \hline Voltage (V) & 100–240 & \\ Frequency (Hz) & 60 & \\ Lumens (lm) & 2000 \(\pm\) 10\% & \\ Efficacy (lm/W) & \textgreater{}100 & \\ Color temp. (K) & 5700 \(\pm\) 300 & \\ Color rendering & \textgreater{}80 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Luminaires specifications of classroom EE-406. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **y = \textasci{-2.61 ln(x)} + 16.118** & \\ \hline
**Human Eye Perception** & **y** & **x** \\
**(Clarity)** & **(Average Luminance, cd/m\({}^{2}\))** \\ \hline The blurriest 20\% & 2 & 223.45 \\ Blurry 40\% & 4 & 103.85 \\ Normal 60\% & 6 & 48.26 \\ Clear 80\% & 8 & 22.42 \\ The clearest 100\% & 10 & 10.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Using clarity degrees to calculate average luminance. * Lighting control method: The classroom is 10 m long and 11 m wide. The luminaires are arranged as (5 \(\times\) 4). There are five rows of luminaires paralleled to the projection screen near the blackboard used for the switch control experiment. * Level A: All of the luminaires are turned on. * Level B: Turn off the first row luminaires. * Level C: Turn off the first and second rows luminaires. * Level D: Turn off the first, second and third rows luminaires. * Level E: Turn off the first, second, third and fourth rows luminaires. * Level F: All of the lights are turned off. * Measure the luminance of the slideshow content: content pictures as shown in Table 1.
* Setting up the image luminance meter: 110 cm height from the ground.