Photoreceptor Enhanced Light Therapy (PELT): A Framework for Implementing BiologicallyDirected Integrative Lighting

Targeting sleep and the circadian system as a novel treatment strategy for Parkinson’s disease

“…It is clear that modulating photoreceptor activation ratios that reflect daylight inputs to the SCN and the retinal pathologies found in PD may present opportunities to develop mechanism based light therapy protocols [ 3 ], such as using light spectra tailored for new photoceutical treatments to better manage the clinical symptoms in PD [ 83 ]. In line with the importance of the timing of drugs, it is likely that these targeted light therapy protocols would need to be adjusted to synchronise with melatonin action (to fall asleep and maintain sleep) and the timing of other medications.…”

“…Indeed, such artificial lighting may even have negative health effects by delivering continuous exposure to lighting spectrums that are not specifically required, a situation akin to taking the wrong dosage of a medication. The functional and structural melanopsin changes in PD provide a strong rationale for specifically targeting the melanopsin photoreceptor using day light spectra designed to target their activity as a novel photoceutical to better manage the clinical symptoms [ 3 , 82 , 83 ].…”

“…Such novel photoreceptor-directed lights can generate complex light spectra and illumination levels to match the change in the relative activity of all photoreceptors in the eye during the solar day through selectively and/or combined activation of melanopsin cells, rods and cones [ 83 ]. One recent study that has finished recruitment has specifically targeted the melanopsin deficits in PD with such biologically-directed light through a randomised, double-blind clinical trial (ACTRN12621000077864).…”

Melanopsin Vision

“…As a result, decreasing the blue light emission of a light source will reduce the level of melanopsin activation, but even blue-depleted light sources will still be capable of driving melanopsin ipRGC responses if of sufficiently high irradiance. A blunt approach such as reducing the correlated colour temperature (CCT) of a light source may lessen melatonin suppression by driving the maximum emission of the light to longer wavelengths, though intentional spectral engineering enables CCT to be decoupled from melanopsin activation (Feigl et al 2022). More sophisticated psychophysical methods to decouple photoreceptor inter-relations are discussed in Section 4.…”

“…12 Future Directions, Unknowns, and Conclusions A comprehensive understanding of the non-image-forming pathways gives rise to an exciting field of so called 'photoceuticals', where light stimuli or lighting environments can be crafted in ways that specifically target non-image-forming physiology (Feigl et al 2022). Just as for pharmaceuticals, careful consideration needs to be given to the dose (intensity), formulation (spectrum), and timing to maximize therapeutic effects while minimizing discomfort or side effects (Lucas et al 2014).…”