## 3 Results and Discussion
### Results of KSS Test  
Figure 12 gives an overview of the subjects' alertness monitored by means of the KSS test. Similarly, there was no statistical differences between the KSS ratings of experienced subjects (Group A, Exp.2) and inexperienced subjects (Group B, Exp.2), as tested by a Mann-Whitney U test (Session 1: \(p\) = 0.26; Session 3: \(p\) = 0.89). Thus, for the KSS test, all the data in Exp.2 were combined.  
Figure 11: Bar chart of the average comfort rating scores with results of Wilcoxon Signed Rank Test (only the \(p\) values lower than 0.05 were marked).  
As shown in Figure 12, the average alertness was always located between \"some signs of sleepiness\" (number 6) and \"rather alert\" (number 4). Surprisingly, the average KSS ratings of Session 1 and Session 3 were almost identical, which indicates that the visual fatigue caused by the two-hour self-study period in Session 2 did not remarkably impact the psychophysical state (sleepiness) of the subjects. This was unexpected and might be due to the intense concentration shown by the subjects during Session 2. As noted earlier, the subjects were busy preparing for their final exams when this experiment was carried out. Therefore, during Session 2, all the subjects worked very hard and thus, kept alert. In further work, it would be of interest to conduct a comparative experiment where the students are not under any pressure (e.g., when they have a relaxing time reading). Despite this, we believe this study has simulated a common and meaningful case for classroom lighting.  
As shown in Table 5, there was no significant impact of lighting environment and gender (including interaction effects) on the subjects' alertness (\(p>0.05\)). Similar results were also obtained by [PERSON] and [PERSON] [60] who compared two lighting environments (average illuminance 232 vs. 352 lux, CCT not reported) and found that there was no measurable influence of lighting on the participants' alertness as quantified by the KSS test. [PERSON] et al. declared, however, that self-reported alertness in the KSS test was improved under blue-enriched white light with a higher CCT [61]. There are two possible explanations for such inconsistency. First, the difference in CCT values between Exp.1 and Exp.2 in our study was not large enough to affect alertness. Specifically, the average CCT values in Exp.1 and Exp.2 were 6600 and 5100 K (\(\Delta\)CCT = 1500 K), respectively, while in [PERSON] et al. [61], the test CCTs were 4000 and 17,000 K (\(\Delta\)CCT = 13,000 K). Second, the interaction effect of CCT and illuminance may also lead to the insignificant differences in KSS results. As shown in Table 1, the CCT values of Exp.1 were higher but the illuminance level of Exp.2 was higher (approximately 300 vs. 150 lux).  
In summary, a significant impact of classroom lighting on visual perception (i.e., skin preference, multi-dimensional lighting atmosphere evaluation) was found, while no measured effects of lighting were observed on the participant's reading comfort, attention, and alertness. The impact of visual fatigue generated by a two-hour, high-intensity, self-study period was insignificant. The influence of proficiency in the Anfimov test was shown, suggesting that a full consideration of a practice effect should be considered when using this or similar tests (e.g., Landolt rings [60] or the D2 test [62]). To solve this, use of a between-subject design in the experimental protocol would be useful. In addition, there was imperfect experimental control due to the inherent limitation of any field study [42]. Thus, as suggested by recent researchers [42; 63], multiple statistical tools were used to demonstrate convincing conclusions.