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Human Research Program

Optimizing Light for Long Duration Space Exploration

Completed Technology Project

Project Introduction

The goal of our work is to optimize lighting that supports vision and serves as a circadian countermeasure for astronauts and ground crew during space missions. Due to recent changes in NASA's objectives for space exploration, NSBRI permitted the re-direction of our original specific aims to augment a separate feasibility, pilot project (NASA #NNX09AM68G). The research we proposed had time-sensitive relevance to implementation of the new lighting system for ISS. NSBRI's decision enabled us to develop two replicas of Crew Sleeping Quarters (CQs) that had similar reflectance and dimensions as those currently onboard the ISS. Prototype solid-state lighting modules (SSLM-Rs) were used to illuminate these laboratory CQs.

One of the new aims was to determine the potency of light emitted by the SSLM-Rs inside of the replicas of the ISS CQs for acute melatonin suppression. In two separate studies, young, healthy subjects were exposed to broad spectrum, white light (CCT of 6,500 K or 2,700 K) emitted by the SSLM-Rs. Completed tasks include: 186 nighttime light exposures, all associated melatonin assays, basic melatonin statistics (t-tests and analysis of variance), and pupillary dilation statistics. Preliminary melatonin suppression curve fits have been completed.

NSBRI support also permitted the investigators to extend the number of subjects studied in the NASA feasibility, pilot study. The original NASA budget plan estimated that 6 subjects could be entered into the protocol. With augmented support from NSBRI, a total of 10 male, astronaut-aged subjects (37.8 +/- 2.7 years) passed extensive screening procedures and entered the 4-day protocol. Nine subjects completed the protocol. Data was collected on visual sensitivity, pre-sleep melatonin secretion, subjective alertness, objective alertness, neurobehavioral responses, and sleep parameters. This pilot study successfully demonstrated the feasibility of using a variety of physiological and behavioral measures within the very confined spaces of the replica ISS CQs.

Despite the overall study being insufficiently powered to fully test hypotheses, the study provided the ability to determine which dependent variables could yield statistically significant results through power analyses. For examples: data on sleep efficiency, total slow wave sleep, and the 3 min psychomotor vigilance test indicated that N=30 per group in a crossover study design should yield statistically significant results. Thus, based on those three dependent variables, a properly powered study with a crossover design would include 60 subjects. The time until the installation of the solid state lighting system on ISS in 2015-2016 is relatively short. Given the intended use of this lighting system for supporting crewmember vision and serving as a countermeasure for sleep and circadian disruption, a study indicated by this power analysis would be valuable for guiding the operational use of this new technology.

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