Elsevier

Acta Astronautica

Volume 92, Issue 1, November 2013, Pages 21-28
Acta Astronautica

Solid-state lighting for the International Space Station: Tests of visual performance and melatonin regulation

https://doi.org/10.1016/j.actaastro.2012.04.019Get rights and content

Abstract

The International Space Station (ISS) uses General Luminaire Assemblies (GLAs) that house fluorescent lamps for illuminating the astronauts' working and living environments. Solid-state light emitting diodes (LEDs) are attractive candidates for replacing the GLAs on the ISS. The advantages of LEDs over conventional fluorescent light sources include lower up-mass, power consumption and heat generation, as well as fewer toxic materials, greater resistance to damage and long lamp life. A prototype Solid-State Lighting Assembly (SSLA) was developed and successfully installed on the ISS. The broad aim of the ongoing work is to test light emitted by prototype SSLAs for supporting astronaut vision and assessing neuroendocrine, circadian, neurobehavioral and sleep effects. Three completed ground-based studies are presented here including experiments on visual performance, color discrimination, and acute plasma melatonin suppression in cohorts of healthy, human subjects under different SSLA light exposure conditions within a high-fidelity replica of the ISS Crew Quarters (CQ). All visual tests were done under indirect daylight at 201 lx, fluorescent room light at 531 lx and 4870 K SSLA light in the CQ at 1266 lx. Visual performance was assessed with numerical verification tests (NVT). NVT data show that there are no significant differences in score (F=0.73, p=0.48) or time (F=0.14, p=0.87) for subjects performing five contrast tests (10%–100%). Color discrimination was assessed with Farnsworth-Munsell 100 Hue tests (FM-100). The FM-100 data showed no significant differences (F=0.01, p=0.99) in color discrimination for indirect daylight, fluorescent room light and 4870 K SSLA light in the CQ. Plasma melatonin suppression data show that there are significant differences (F=29.61, p<0.0001) across the percent change scores of plasma melatonin for five corneal irradiances, ranging from 0 to 405 μW/cm2 of 4870 K SSLA light in the CQ (0–1270 lx). Risk factors for the health and safety of astronauts include disturbed circadian rhythms and altered sleep–wake patterns. These studies will help determine if SSLA lighting can be used both to support astronaut vision and serve as an in-flight countermeasure for circadian desynchrony, sleep disruption and cognitive performance deficits on the ISS.

Highlights

► Research was done inside a high-fidelity replica of the ISS Crew Quarters (CQ). ► A Solid-State Lighting Assembly (SSLA) for the ISS was used to illuminate the CQ. ► High levels of SSLA light significantly suppressed plasma melatonin inside the CQ. ► SSLA light allows for contrast and color vision similar to room light and daylight.

Introduction

Known risk factors for the health and safety of astronauts and ground control workers include disturbed circadian rhythms and sleep loss [1], [2]. Sleep and circadian problems have been documented in space flight missions as short as 10 days [3]. An analysis of pharmaceutical use during 79 space flight missions showed that sleeping pills or hypnotic compounds accounted for 45% of all medications taken by 219 astronauts [4]. Despite the use of these drugs, studies of more than 60 astronauts on space shuttle (Space Shuttle Transport System or STS) missions showed that approximately half of them slept 6 h or less per 24-hour mission day, even though they are scheduled to sleep for 8 h [5]. Chronic partial sleep loss can pose a considerable threat to the success of a mission by diminishing alertness, cognitive ability and psychomotor performance [3], [6], [7], [8], [9], [10].

The International Space Station (ISS) uses General Luminaire Assemblies (GLAs) that house fluorescent lamps for illuminating the astronauts' working and living environments [11]. Solid-state light emitting diodes (LEDs) are attractive candidates for replacing the fluorescent lighting system on the ISS. The advantages of LEDs over conventional fluorescent light sources include lower up mass, power consumption and heat generation, as well as fewer toxic materials, greater resistance to damage and long lamp life [12]. A prototype Solid-State Lighting Assembly (SSLA) was developed at Kennedy Space Center and successfully installed on the ISS during Expedition 18. Since then, NASA has developed a set of specifications for the solid-state lighting system that will replace the existing fluorescent lighting system onboard ISS [13]. This new lighting system will provide multiple settings that can support astronaut vision and potentially serve as a lighting countermeasure for performance decrements due to sleep and circadian disruption aboard the ISS.

It is crucial to characterize the new solid-state lighting units for their circadian, neuroendocrine and neurobehavioral efficacy as well as their capacity to support astronaut vision. Non-visual information about light is detected by the eyes and transmitted by the retinohypothalamic tract, a neural pathway which projects to both visual and non-visual regions of the human brain [14], [15]. These neural centers receive environmental photic input from a specialized subset of photoreceptive retinal ganglion cells containing the photopigment melanopsin [14], [16], [17], [18]. It has been demonstrated that more light is required for circadian, neuroendocrine and neurobehavioral regulation than is needed for vision [19], [20], [21]. Further, a different wavelength sensitivity has been identified for the non-visual regulation of physiology and behavior compared to stimulating visual responses [22]. For example, studies have shown that exposing humans to light of sufficient intensity and duration at night suppresses the pineal gland hormone melatonin, with the strongest response occurring between 446 and 477 nm, the portion of the spectrum that has a blue appearance [23], [24]. Further research has shown that blue monochromatic light at 460 nm is more effective than longer wavelength light at 550–555 nm for phase-shifting circadian rhythms and enhancing alertness levels [25], [26], [27]. In contrast, daytime vision has a peak sensitivity to light at 555 nm [28].

The broad aim of the ongoing work is to test light emitted by prototype SSLAs for supporting astronaut vision and assessing neuroendocrine, circadian, neurobehavioral and sleep effects. Three initial ground-based studies were conducted inside of a high-fidelity replica of the ISS Crew Quarters (CQ). The four CQs onboard ISS are acoustically quiet, visually isolated areas for crewmember sleep, relaxation and private retreat [29], [30]. The studies presented here include experiments on visual performance, color discrimination, and acute plasma melatonin suppression in cohorts of healthy, human subjects under different SSLA light exposure conditions.

Section snippets

Light production

The experimental light exposure system used in this study, the Solid-State Lighting Module-Research (SSLM-R), was based on the SSLA prototype installed on ISS in terms of mechanical and electronic connectivity. The SSLM-R, however, was developed as a research tool with significantly expanded capacity for variable light outputs. The SSLM-R was developed at Kennedy Space Center (Bionetics Corporation, Cape Canaveral, FL) and contained LED arrays of 294 white LEDs and 254 RGB LEDs behind a lens

Visual performance test results

ANOVA showed no significant differences between lighting conditions for time (F=0.13, p=0.88) or score (F=0.34, p=0.72). Significant differences were found between contrast levels for both time (F=27.93, p<0.0001) and score (F=18.38, p<0.0001). Using a Dunnett's t-test post hoc analysis, it was found that 10% contrast differed significantly from all other contrasts for both time and score (p<0.005; Fig. 2).

Color discrimination tests

ANOVA showed no significant differences for FM-100 score between the three lighting

Discussion

The present data demonstrate that bright white 4870 K SSLM-R light inside of the CQ supports visual performance and color discrimination equivalently to typical indoor exposures to indirect daylight and overhead fluorescent light. In addition, increasing irradiances of this white solid-state light inside the CQ elicit increasingly stronger melatonin suppressions in healthy volunteers. These findings demonstrate the feasibility of doing controlled studies on visual, neuroendocrine and circadian

Acknowledgments

This work is supported by the National Space Biomedical Research Institute through NASA NCC 9-58 and NASA #NNX09AM68G. Special thanks to Daniel Schultz of Kennedy Space Center, Matthew Regan and Trevor Murdock of Bionetics Corporation, and Fred Maxik and Robert Soler of the Lighting Sciences Group for the development of the SSLM-Rs used in this research. Additional thanks to Dennis Grounds and Lauren Leveton, Ph.D. of Johnson Space Center for donation of the SSLM-Rs to our laboratory. Many

George C. Brainard, is a Professor of Neurology and the Director of the Light Research Program at Jefferson Medical College of Thomas Jefferson University in Philadelphia, PA. His academic work has been concerned with the effects of light on biological and behavioral responses of animals and humans for over thirty years. He currently serves as the National Space Biomedical Research Institute Team Leader for Human Factors and Performance that involves five universities working collectively to

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    George C. Brainard, is a Professor of Neurology and the Director of the Light Research Program at Jefferson Medical College of Thomas Jefferson University in Philadelphia, PA. His academic work has been concerned with the effects of light on biological and behavioral responses of animals and humans for over thirty years. He currently serves as the National Space Biomedical Research Institute Team Leader for Human Factors and Performance that involves five universities working collectively to develop solutions for health risks during spaceflight.

    William Coyle, has over 30 years experience as a cabinetmaker, woodworker and general remodeler. His work includes fabricating and installing custom cabinetry in homes and offices as well as general remodeling activities. He has also assisted the Jefferson Light Research Lab at Thomas Jefferson University in Philadelphia, PA for over 25 years fabricating and installing custom cabinetry to support and assist the Light Lab team in their research activities. He designed and built the CQ used in the current study.

    Melissa Ayers, M.S., holds a double B.S. in electrical engineering and biomedical engineering from Drexel University, as well as an M.S. in neuroscience from Thomas Jefferson University. She has been involved with the Light Research Program at Thomas Jefferson University for the past five years. She is the primary subject recruiter, and also assists with data analysis, study design, as well as grant, manuscript, and report writing.

    John Kemp, is a graduate of Rutgers University, New Brunswick, NJ and possesses Dual B.A. Degrees in Economics and Communications. For over two years, he has worked as a Research Technician at the Light Research Program at Thomas Jefferson University in Philadelphia, PA. As a member of the team, his duties include: contributing in study planning and design, performing studies, data entry/analysis, and assisting in the preparation of manuscripts, grant reporting and renewals.

    Benjamin Warfield, has been a part of the Jefferson Light Research Program for over 8 years, initially contributing on imaging and archival work for the 2003 NSBRI grant, then moving into a full time research technician post working on nighttime melatonin studies. He is now the lab operations support specialist, developing scientific posters and assisting with the lab's applied space research and dark-sky awareness projects while continuing to archive pineal research from the past.

    James Maida, has been at Johnson Space Center for over two decades. In that time, he has been a technical monitor for the JSC Graphics Research and Analysis Facility (GRAF), the JSC Lighting Environment Test Facility (LETF), and the Anthropometry and Biomechanics Facility (ABF). He has also worked on the development and integration of the lighting analyses capability into the Shuttle and ISS programs. He has also served as real-time mission support with lighting analyses for crew timelines during berthing for ISS assembly using SVS.

    Charles Bowen, Ph.D., previously designed analog, digital, and power electronics primarily for commercial seismic data acquisition systems for 19 years. This experience afforded practical insights into the operation and limitations of semiconductors and power system components that have applications for practical LED lighting. For the past 8 years, he performed the role of human factors design engineering specialist in the Lighting Environment Test Facility (LETF) at NASA/Johnson Space Center's Habitability and Environmental Factors Division. This position has afforded many opportunities to investigate technical aspects of a variety of lighting systems proposed for/used in NASA spacecraft.

    Craig Bernecker, Ph.D., FIESNA, LC, has directed the lighting program at Penn State University, and developed lighting education programs in distance education, as well as served on the policy-advising body for the Penn State World Campus. He has published more than forty articles on lighting and is known for his work on the psychological aspects of lighting. He maintains an active consulting practice and regularly serves as a peer reviewer for the U.S. Department of Energy. Dr. Bernecker has served the Illuminating Engineering Society (IES) of North America in several capacities, including President for 2004-2005. He was named an IES Fellow in 1991.

    Steven W. Lockley, Ph.D., is a neuroscientist at Brigham and Women's Hospital, and an associate professor of medicine at Harvard Medical School. His research focuses on human circadian biology. Specifically, his research includes the effects of timing, duration, intensity and wavelength of light exposure on circadian resetting, melatonin suppression and the acute alerting effects of light, as well as the visual impairments and the effects of the severity and type of blindness on circadian photoreception, the periodicity of the circadian pacemaker and development of circadian rhythm sleep disorders.

    John P. Hanifin, M.Phil, Over the past 24 years, he has been an active contributor to the field of pineal research as evidenced by authorship on 2 and co-authorship on 20 peer-reviewed papers in the field. As the laboratory manager for the Jefferson Light Research Program of Thomas Jefferson University, he coordinates and integrates lab staff; assists in grant and manuscript writing; maintains policies and procedures involving human subjects; oversees subject recruitment, testing, and scheduling for ongoing light research studies; and manages government and industry grant support. He is currently in a Ph.D. collaborative program in Biochemical Sciences at the University of Surrey.

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