## 7 Conclusions and Future Directions  
We have highlighted the current evidence on the importance of lighting design in healthcare environments for promoting proper circadian alignment and its associated health outcomes, providing insights into the diverse health benefits that may be achieved through biologically appropriate lighting designs and conditions in healthcare settings. In total, twenty-six sources assessed lighting conditions and systems in healthcare environments from a circadian health perspective. Among them, twenty-one papers focused on the interventional human subject studies. The body of neuroscientific and biological evidence indicates that exposure to natural light cycles has positive health and well-being benefits for human, including reduced fatigue, increased alertness in healthcare providers, and positive patient and family experiences. However, the reviewed papers provide mixed views on the health benefits of ALAN exposure in institutional environments; the lack of consistent results likely reflects the paucity of research in this emerging area. Despite some arguing for the benefits of adjustable lighting systems with the aim of mimicking natural light, other studies have reported conflicting or inconclusive results. Five papers were simulation-based and conducted across various latitudes, appropriate window design and ratio, interior spatial properties to ensure that the indoor lighting conditions are healthy for patients and staffs. Qualitatively, the positive outcomes of some studies suggest that pursuing institutional natural and artificial lighting designs is a beneficial approach; however, the low number of studies prevents a quantitative assessment of the current evidence in the field. Thus, there remains much to be explored regarding the efficacy of artificial lighting designs in healthcare facilities, necessitating more rigorous control interventions and more comprehensive experiments within well-controlled environments, and replication of these studies considering the multifaceted influence of various parameters on circadian health. Further research in this field is required to establish conclusive evidence. In addition, implementing circadian-aligned lighting designs in healthcare environments requires collaborative efforts among architects, lighting designers, healthcare professionals, and researchers. Artificial lighting systems, including spectrally tailored lighting and personalized bio-adaptive lighting, can supplement daylight and modulate light intensity and spectrum according to circadian needs; robust full spectrum lighting during the day and minimal (sub-individual melatonin suppression level) ALAN exposure. The integration of lighting control technologies, such as dynamic adjustment of light levels and color temperature based on natural light availability and time of day, is essential for achieving circadian alignment. These technologies, combined with occupancy and daylight sensors, can optimize energy efficiency while maintaining proper sleep-wake cycles. Along with additional lighting simulations and additional studies with the consistence use of standardized lighting metrics for evaluating and optimizing lighting designs in healthcare settings, designers will be able to make informed decisions about lighting design, ensuring that buildings offer healthy, comfortable, and visually appealing environments that promote well-being, productivity, and energy efficiency.