That the changes were larger in the objective measures (e.g., salivary melatonin onset, pupil light reflex) with the enhanced melanopsin condition (Enhanced Mel) indicates a greater physiological effect, but reaching statistical significance compared to a daylight may require a longer intervention period or may only be observed in the more advanced stages of PD where more extensive melanopsin loss might be expected. Here, OPN4 is linked to Parkinson disease.