## 5 Results and Discussions
Following the results for the morning, the first period after lunch and the closing hours of the working day are represented and finally, a general diagram for the fatigue level in the time horizon of the working day is presented. The results obtained through the experiments confirm what it is present in the literature for the chrono-types analyzed in this research. All subjects investigated have less sleepiness at the beginning of the shift while the maximum level occurs at the end of the shift, following an increasing trend differentiated between the two main investigated sets of chrono-types. Subjects considered to belong to the morning rhythm have a lower level of fatigue during the morning compared to subjects characterized by an evening rhythm, which, however, have a lower level of fatigue at the end of the shift. Of particular interest is the very marked increase that occurs in people over the age of 35 in the post-lunch break interval: unlike the other category, their fatigue level is double, compared to the morning one; in practice, the fatigue appears not reduced by the lunch break. The motivations of this phenomenon could be their eating habits, behavioral, or in the different personal management of sleepiness. It is worth to note that these last issues will not be faced in this research, as it is focused on the technological experimentation for fatigue detection. In all the afternoon records it is possible to notice a decrease in the non-detected result related to the lighting that increases due to the lighting  
Figure 10: Results of the experiments in the afternoon for the evening circadian chrono-type. Figure 9: Results of the experiments in the period after lunch for the evening circadian chrono-type. of the artificial lights. Therefore, it is possible to affirm that the software is very sensitive to these environmental factors. In the last figure (Figure 11) it is reported a comparison diagram in which it is possible to understand the different shape of the curves for the two chrono-types analyzed in this experimental study and also the differences in absolute values of fatigue for both of them during the entire time span of a working day. The FF (the false fatigue results of experiments) result is linked to intrinsic criticalities of the software used for the analysis and is common to all registrations; an exhaustive list follows. The program used, even though it has many features that could make it usable in productive contexts, has several critical issues that have to be fixed for its full application in the production context:  
* One of the most significant critical points is the sensitivity to the rotation of the face and the direction of the gaze: when the subject focuses his gaze in a direction different from that of the camera, the eyes appear to have a different opening, although this is not associated with any state of fatigue. In this case, the program gives the result of \"fatigue\" as the eye is recognized as closed. This criticality was recognized in the experiments and to avoid it, all the experiments records were analyzed and when this criticality was recognized the experiment result was indicated as \"False Fatigue\". The presence of beard in the subject, especially if thick, often results in \"Fatigue\", recognized through visual verification as False Fatigue, as the mouth is incorrectly detected as open, generating the alarm associated with yawning. This criticality is probably due to the limited presence of bearded individuals in the database. * The ambient lighting was very incisive in the evaluation, especially in the late afternoon recordings causing the majority of the non-detected results. Another criticality of the software was identified in the difficulties to read the face and eye shape when the subject analyzed has glasses. Another improvement of the software when it is applied to the production context could be related to the yawing detection that in the driving sleepiness detection could be of interest, but in the production context not necessarily.