We present the first lighting system to be designed to accommodate the new knowledge of sunlight coupled physiology. To our knowledge, this is the only cycled lighting system that generates wavelengths capable of OPN5 activation. This allows careful interrogation of the activity of OPN5 in a clinical setting. While the NICU is a compelling place for this initial phase of translational investigation, many opportunities exist in other locations such as long-term behavioral health facilities and other sites for management of chronic conditions. A growing body of evidence directly implicates OPN5 and violet light exposure to the progression of myopia and retinopathy of prematurity (15); (16). There is also substantial interest in the impact of the cycled lighting environment for providers and families. The ability to move from generic light-dark cycling to dynamic full-spectrum lighting that mimics natural variation in spectral composition from sunrise to sunset represents an important advance.
It is important to distinguish the spectral capacity of the NICU lighting system from lighting that varies color temperature over the course of a daytime period. Color temperature measures visual perception of light rather than actual spectral distribution. For example, the perception of violet can be created without the generation of wavelengths in the violet spectrum. Without violet photons, OPN5 stimulation will not occur.
At this early stage of translational research there are many unanswered questions. The “dose” of light needed to activate OPN5 is not precisely defined. Preclinical studies demonstrate that sufficient photons reach deep brain structures in mice to stimulate OPN5 (11). Similarly, a growing body of studies document activation of OPN3 and OPN5 in a variety of non-ocular locations such as skin and adipose tissue (10); (17). Opsins demonstrate absorption spectra over a range of wavelengths. For example, OPN5 can be stimulated at different efficiencies from 340-420 nm. Correlation of absorption spectrum to biological effect in a real-world clinical setting will require additional study.
Our growing understanding of OPN3 and OPN5 implies their fundamental role in metabolic activities and energy homeostasis. Many conditions encountered in the NICU are associated with growth failure such as gastroschisis, intestinal failure/short bowel, and bronchopulmonary dysplasia. The significance of body composition for neurodevelopmental outcome is an area of increasing interest for the NICU population. Circadian influences on energy management are likely to be very relevant to common NICU practices such as enteral feeding protocols and parenteral nutrition. For example, time of day and exposure to relevant daylight wavelengths may profoundly influence how a neonate utilizes macronutrients and energy substrate. Post-discharge outcomes, such as visual acuity and neurobehavior, may also be impacted.
As we consider environmental light exposure in the context of neonatology practice, many questions remain. The dose of daylight, including duration of exposure, intensity, and key wavelengths will require further refinement. This is particularly interesting when deep tissue structures expressing light-sensing opsins are considered. Electromagnetic wavelengths outside of the visual spectrum (infrared and ultraviolet) are also known to influence certain biologic processes through non-opsin mediators. Our focus here is restricted to wavelengths within the visual spectrum known to activate human opsins. Finally, energy management, utilization of macronutrients, and growth are fundamental to survival. It is reasonable to expect that pathways regulated through opsin stimulation are relevant to human growth and development. Our NICU lighting system will now allow interrogation of these pathways, supporting the further optimization of growth and development during a crucial stage of life.