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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorFigueiro, Mariana Gross
dc.contributorRea, Mark Stanley, 1950-
dc.contributorNarendran, Nadarajah
dc.contributorKalsher, Michael J.
dc.contributor.authorNagare, Rohan
dc.date.accessioned2021-11-03T09:16:19Z
dc.date.available2021-11-03T09:16:19Z
dc.date.created2020-08-10T12:03:28Z
dc.date.issued2019-12
dc.identifier.urihttps://hdl.handle.net/20.500.13015/2507
dc.descriptionDecember 2019
dc.descriptionSchool of Architecture
dc.description.abstractGiven the advent of non-conventional white light sources devoid of specific short-wavelength radiation (such as the “cyan-gap”), and recent electrophysiological evidence suggesting greater neural complexity of phototransduction pathways in retina, a primary objective of this thesis was to provide further resolution with regard to the spectral sensitivity framework proposed by Rea and colleagues. Another objective was to add a dynamic exposure duration factor to the CS model, as the current model only accounts for a fixed exposure duration of 1-h, and there exists strong evidence suggesting that exposure duration affects the circadian efficacy of the photic stimulus in non-linear manner. The model is also largely static with regard to accounting for physiological traits of the population, hence, the thesis also aimed to describe age and macular pigment optical density (MPOD) induced changes to the spectral and absolute sensitivities of the human circadian system. Overall, six nighttime studies with salivary melatonin suppression as the dependent variable were conducted between February 2017 and May 2019, to improve and extend the original model. Collectively, participants from distinct age-groups and varying MPOD values (0.02 – 0.81) were exposed to a specialty white light source (“cyan-gap” with reduce radiant power between 475 and 495 nm) and several other conventional white light sources (rated correlated color temperatures or CCTs – 2700 K, 3300 K, 4000 K, 4300 K, 5000 K and 6500 K), at varying light levels (40–1000 lux ) and exposure durations (0.5–3.0 h). In the wake of ambiguity concerning the ability of the circadian system to integrate photic stimuli spatially, a study was also conducted to examine how two different lighting distribution patterns for a narrow-band light LED source (451 nm) could affect nocturnal melatonin suppression.
dc.description.abstractThe ability of the CS model to accurately predict circadian effectiveness of unconventional light sources (such as cyan-gap), should be of particular interest to lighting manufacturers who are interested in producing light sources that can have a differential effect on the circadian system without affecting photopic light levels and CCTs. The results also have an important bearing with regard to specifying circadian lighting for patients afflicted with Alzheimer’s diseases and related dementia (ADRD), which often are diagnosed with low MPOD values. Rea et al. model of human circadian phototransduction, in conjunction with parallel development of tools such as Daysimeters and Web CS calculator, provides reliable metrics and instrumentation to aid in lighting design at institutes and residences housing ADRD population, appropriate for both human visual and circadian systems. For instance, in the wake of frequent nocturnal wandering of the ADRD patients, the extended CS model could help specify nighttime light levels bright enough to promote visual functioning and safe navigation, without affecting melatonin secretion upon longer exposure durations.
dc.description.abstractA revised framework has been proposed which extends the original model to more accurately reflect participation of all classical photoreceptors in the primary rod pathway via the shunting AII amacrine cells. Goodness of fit to melatonin suppression data for polychromatic sources increased from 0.85 (original model) to 0.97 (revised model). Results from the MPOD studies collectively indicate that a lower MPOD was associated with greater melatonin suppression, and that the between-subject differences in MPOD, could present a novel way to depict the notch within the spectral sensitivity of the human circadian system without changing light source spectrum. Results from the final study showed that changing spatial distribution from an ON-axis orientation to an OFF-axis orientation results in a more than 50% drop in circadian efficacy of a narrow-band blue light source in suppressing melatonin at night, while also unexpectedly implicating macular pigment in affecting absolute sensitivity of peripheral photoreceptors. In the future, it is imperative to develop a spatial correction factor for all model predictions.
dc.description.abstractTaken together, the results from all the studies are consistent with those from many previous studies showing that higher light levels and longer exposure durations result in greater melatonin suppression. A univariate exposure duration factor was added to the CS model absolute sensitivity to reflect the results showing that the light’s incremental effectiveness for suppressing melatonin diminishes with increasing exposure duration, irrespective of spectrum or participant age, during the early part of the biological night when melatonin levels are rising. Validation analysis using a nonlinear least squares method revealed that predicted responses from the duration extended CS model, significantly matched the measured responses (for all except 2.5-h dataset) from past studies conducted by Lighting Research Center, as well as, other labs in the field. In regard to the spectral sensitivity, it was found the melanopsin-only spectral sensitivity for warm polychromatic light sources is lacking important inhibitory contributions to the retinal ganglion cells from rod photoreceptors.
dc.description.abstractCircadian disruption, caused by a misalignment between endogenous biological rhythms and local solar time, as might occur between preferred sleep patterns and school or work schedules, can lead to social, behavioral, and metabolic health problems in humans. Given that the human circadian system is primarily regulated by the 24-h light-dark cycle incident on the retina, an understanding of underlying phototransduction mechanisms is essential for specifying lighting design to benefit human health and well-being. In 2005 and as revised in 2012, Rea et al. proposed a subadditive model of human circadian phototransduction, based on the effects of retinal light exposures on nocturnal melatonin suppression, which is consistent with the neuroanatomy and physiology of the human retina. The model has been extensively used in the laboratory and the field to predict efficacy of light exposures on clinically relevant outcome measures, such as sleep onset time, demonstrating its scientific and face validity.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectArchitectural sciences
dc.titleRevising and extending the model of human circadian phototransduction
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid179996
dc.digitool.pid179997
dc.digitool.pid179998
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentSchool of Architecture


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