## 4 Discussion
### Lighting Design and Automation Rationale
As such, their effect might beneficial in the high and low melanopic settings. The implications of the differences in MEDI between an unobstructed sensor to one with a field-of-view obstruction (Table 2) are not clear at present, as recommendations for melanopic stimuli stem from experiments without a FOV obstruction. [PERSON] et al. [26] showed MEDI differences between 12% and 74% for an office setting. These values are in between those of the _quality control_ and _packaging_ workplaces showed here. A large reduction, such as that present at the _packaging_ workplace (23-114%), likely benefits a low melanopic setting, as at least some light reaches the eye outside the field of view. For the same reasons, it will likely reduce the nonvisual effect for a high melanopic setting. When the _Drosa_ luminaire is placed near the worker and the task, such as in the _quality control_ workplace, the difference between the two measures is negligible (3-4%). The potential to change the melanopic stimulus in a meaningful way must be realized through a robust automation system. This ensures the intended light dosage and timing, which are of supreme importance [17; 48]. Our goal for the automation was to strengthen the circadian rhythm of the rapidly rotating shift workers, thereby reducing the negative effects of chronodisruption. The strategy is opposed to recommendations of bright, blue light at night, which would increase alertness and acute performance [49] but come at the cost of unintended phase shifts, reduced sleep quality, and long-term health detriments [19]. Compared to the stock lighting, which provided a high melanopic stimulus throughout day and night, we designed the automation system with the following rationale for nonvisual aspects:  
1. Provide an activating and synchronizing stimulus during the morning hours. According to the technical specification DIN SPEC 67600 [29], a melanopic stimulus of 240 lx MEDI is recommended for synchronization, and it activates the user by increasing alertness, wellbeing, and performance. The specification predates the MEDI notation; therefore, the recommendation was converted from 250 lx at 8000 K fluorescent light. [PERSON] et al. [17] showed that the morning hours are best to phase shift the internal clock backward, with a phase response curve constructed from a laboratory experiment. This is supposed to counter opposing phase shifts through light and activity at night. 2. Provide an activating and circadian amplitude strengthening stimulus at the beginning of the evening shift. The activating effect mirrors the one in the morning. At that time of day, workers would also still be able to receive at least similar levels of daylight, if they were outside. [PERSON] et al. [18] showed that increased daytime illuminance reduces the suppression of melatonin through the light the following night. This stimulus might similarly benefit the workers in our project. 3. At night (starting at one hour after sunset), the melanopic stimulus is to be minimal. This reduces both the suppression of melatonin and the forward phase shift induced by light at night [50; 51]. On the negative side, the stronger activating effect of the stock lighting is also reduced. As a target stimulus, we set 100 lx as the upper threshold. While there is no recommendation for this particular value, we decided on it as a realistic lower threshold regarding the high visual illuminance requirement (Table 1) [26]. 4. Starting with the middle of the night shift, the visual stimulus is increased to promote alertness. Sleepiness inevitably rises during the night shift [49]. Some studies show, however, that alertness can be increased by a brighter light, independent of the melanopic stimulus and its detrimental effect on phase shift and melatonin suppression at night [50; 52; 53]. We do not expect this effect to fully compensate for the increasing sleepiness during the shift, but it might have an attenuating effect. If possible, the melanopic stimulus should not cross the threshold of 100 lx set for the night.