## 5 Challenging Methods to Include Occupants Visual Comfort Perception Variance
### Eye Response to Light Variations  
From the gathered literature, only a few metrics were found to directly assess the human eye response to the lighting environment, or indirectly account for the possibility of eye adaptation. These metrics are mostly based on the eye kinematics and only slightly on the quantity of light (either \(E\) or \(L\)). The identified metrics are summarized below:  
* **Pupil diameter (\(d\)):** studied and condensed satisfactorily by [PERSON] and [PERSON] [82]. An index is calculated based on the relationship between the pupil size and the luminance emitted towards it. It is grounded on a compendium of studies performed on human subjects for the medical research field of optometry. Equation (5) presents the most simplified form. Meanwhile, Equation (6) presented a greater correlation accuracy, especially when the corrected form of retinal illuminance (\(E_{R}\)) is used (Equation (7)) instead of the non-adjusted one (Equation (8)). \[d=4.9-3\times\tan h[0.4(\log L+0.5)]\] (5) \[\log E_{R}=\log L+1.8614-0.000986\times(\log L+6.5)\] (6) \[\log E_{R}=10\times r^{2}\times L\] (7) \[\log E_{R}=10\times r^{2}\times L\times\Big{(}1-0.0425\times r^{2}+0.00067 \times r^{4}\Big{)},\] (8) where: \(E_{R}\): retinal illuminance [trolands] \(d\): pupil diameter [mm] \(r\): pupil radius [mm] \(L\): luminance of the visual field [miliamberts]
* **Normalized pupil size (NPS):** [PERSON] and [PERSON] [85] presented an analysis on how using a normalized pupil size value correlated to qualitative visual sensation communi  
Figure 3: Description of the new concept for building components operation, shifting from monitoring the indoor physical conditions into monitoring the hosted occupant’s body’s physiological condition. cated by the tested human subjects. The pupil size was obtained using a dedicated pupilometer, and the \(NPS\) was computed using Equation (7). \[NPS=\frac{Ps_{i}-Ps_{neutral}}{Ps_{neutral}}\times 100, \tag{9}\]  
where:  
\(Ps_{i}\): pupil size at the current state [mm]  
\(Ps_{neutral}\): pupil size at a neutral lighting state [mm]
* **Task-evoked Pupillary Response (TEPR):** [PERSON] et al. [86] studied the pupil diameter variations when different task and lighting conditions were imposed to the human subjects, measured by head-mounted eye trackers and remote eye trackers using image processing (i.e., counting the pixels composing the pupil). * **Pupil diameter-unified formula (\(D_{U}\)):** [PERSON] and [PERSON] [91] presented a review on the previous research carried out to correlate the pupil response to lighting stimulus, highlighting the equation's accuracy, and their potential adjustments. Moreover, it proposed to combine different effects that tend to deviate the pupils' diameter calculation (i.e., \(L\), age, field size and the monocular effect) to construct Equation (10) (applicable for occupants aged between 20-83). \[D_{U}=D_{SD}+A\] (10) \[D_{SD}=7.75-5.75\Bigg{(}\frac{(La/846)^{0.41}}{(La/846)^{0.41}+2}\Bigg{)}\] \[A=(y-y_{o})\times S\] \[S=0.021323-0.0095623\times D_{SD},\] where: \(L\): luminance [cd/m\({}^{2}\)] \(a\): area [deg\({}^{2}\)] \(y\): age of the human subject \(y_{o}\): minimum/reference/benchmark age
* **Degree of Eye Opening (DEO):** [PERSON] et al. [79] presented an analysis on how to use a normalized eye (or eyelid) height value. The pupil size was obtained using an analysis of images recording the state of the eyelid in correspondence with the maximum eye height (Equation (11)). \[\log E_{R}=\log L+1.8614-0.000986\times(\log L+6.5)\]0 (11) where: \(h_{i}\): eye/ eyelid height [mm] or [pixels] \(h_{max}\): maximum eye/eyelid height [mm] or [pixels]
* **Gaze driven illuminance (\(E_{\text{pg}}\)):** [PERSON] et al. [92] exposed an analysis of how much would it change to compute the \(E_{v}\) considering accurately occupant's gaze direction, aided by the use of Radiance images and evalglare tool [63; 66].