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Optimizing Light for Long-Duration Space Exploration

Principal Investigator:
George C. Brainard, Ph.D.

Thomas Jefferson University

During a space mission, sleep and biological rhythm disruption can reduce crew performance and safety. A countermeasure to these disruptions is light, which plays a key role in many different aspects of healthy human body performance – vision, alertness, hormonal regulation and control of biological rhythms. Bright white fluorescent lighting is used as a countermeasure during pre-launch activities, but it has not been used in flight within a spacecraft or habitat.

Dr. George C. Brainard and his colleagues are building on previous research to determine the best wavelengths and intensities of light to reduce sleep and biological rhythm disruption during spaceflight. Brainard is studying healthy men and women to determine the countermeasure potential of solid-state light sources being considered for the International Space Station as well as vehicles and habitats being developed for future space missions. Additional studies on human volunteers will determine the potency of ambient light transmitted though the spacesuit visor during spacewalks. This research could also benefit spaceflight ground support personnel and workers in other industries such as health care, manufacturing and homeland security.

NASA Taskbook Entry

Technical Summary

The goal of this project is to determine the optimal lighting for use as a countermeasure to sleep and circadian disruption for astronauts. Sleep deficits that diminish alertness, cognitive ability, and psychomotor performance are a serious risk factor during space missions. Currently, over 45 percent of all medications taken in space are sleep aids (Putcha et al., 1999). Despite their use, more than half of the astronauts still get only between three and six hours of sleep per night during spaceflight (Barger et al., 2009).

Light is the primary stimulus for human circadian regulation. On Earth, humans have a 24-hour day/night cycle to maintain healthy circadian entrainment. In space, astronauts must contend with either rapidly changing or severely disrupted day/night cycles and must work in a dimly lit spacecraft interior with few windows.

Bright white light has been implemented as a pre-launch countermeasure but has yet to be used during spaceflight. Providing sufficient light intensities to work areas in the International Space Station (ISS) as well as future vehicles and habitats, raises several concerns, among which are heat production, energy consumption and up-mass. Improving these factors requires a better understanding of how different light sources regulate the human circadian system. From these data, it may be possible to optimize astronaut and ground crew light exposure both as a stimulus for vision as well as a countermeasure for sleep and circadian disruption during space missions.

Currently, NASA uses white fluorescent light for interior illumination of the ISS at relatively low intensities, and for a pre-launch lighting countermeasure for circadian disruption at much higher intensities. In the previous funding period, our NSBRI research was supported to determine if those fluorescent lamps have increased efficacy for melatonin suppression and circadian phase-shifting when they are enriched in the blue portion of the spectrum. Philips Lighting, an NSBRI industry partner, provided prototype blue-enriched lamps and exposure systems for that study. In addition, we began characterizing the circadian potency of ambient extraterrestrial light that astronauts will encounter on the surfaces of the Moon and Mars.

To develop an in-flight lighting countermeasure for space exploration, it is vital to determine the sensitivity of astronauts' circadian systems to both ambient and artificial lighting stimuli. In the current period of research, we are shifting our efforts from testing fluorescent light sources to testing solid-state lights. Artificial illumination for future space vehicles and habitats will be provided predominantly by light emitting diodes (LEDs).

Specific Aims

  1. Determine the neuroendocrine, alerting, and circadian potency of light emitted by the white LEDs being considered for re-lamping the ISS as well as lighting future vehicles and habitats. For this aim, we have had four 4’ x 4’ white LED lighting systems installed in our laboratory. These systems emit white light with CCTs of 4,000 K or 6,500 K. To date, 15 healthy subjects have entered into two separate studies and completed over 150 nighttime melatonin suppression studies. The majority of plasma samples collected in these studies have been assayed for melatonin content.
  2. Evaluate selected polychromatic LED stimuli for supporting visual performance, color discernment, and neuroendocrine potency inside replicas of ISS Crew Sleeping Quarters (CSQ). The replica CSQs are illuminated by the ISS prototype solid state lamps (SSLM-R). To date, 16 healthy subjects have participated in two separate nighttime melatonin suppression studies within replicas of the CSQs illuminated by white SSLM-R light with a CCT of 4,800 K. The majority of plasma samples collected in these studies have been assayed for melatonin content. In addition, two studies were done on visual performance and color discernment within replicas of the CSQs illuminated by different polychromatic light stimuli emitted by SSLM-Rs. Analysis of data from these studies is in process.
  3. Compare the potency of ambient light on the surface of Earth and Mars for melatonin regulation. In collaboration with Dr. Peter Smith of the Lunar and Planetary Laboratory at University of Arizona (UA), optical elements were developed and installed for simulating Earth daylight in a Ganzfeld dome. To date, nine astronaut-aged, healthy subjects have and completed 78 nighttime melatonin suppression studies relative to Ganzfeld simulation of Earth daylight. In parallel, the engineers at UA have developed a newer exposure system that simulates ambient Earth, Moon, and Mars light in a larger, non-Ganzfeld environment. Currently, this equipment is being installed in our laboratory for radiometric and photometric assessment.

Together, the research from the two prior funding cycles along with the studies performed in the past year provide significant progress towards the development of lighting countermeasures for sleep and circadian disruption in astronauts and ground crew members. Programmatically, it has provided information that was used in the revision of Constellation Program Human-Systems Integration Requirements (December, 2009). Further, the results will also impact the NASA Human Integration Design Handbook and the Space Flight Human Systems Standard, NASA-STD-3001 that provide guidance for crew health, habitability, environment, and human factors in human spaceflight. Our progress addresses Critical Risk areas 9 (EVA 7) and 22 (Sleep 5, 9, and 10) in the NASA Human Research Program Integrated Risk Plan (2009). These areas concern countermeasures that will optimally mitigate performance problems associated with sleep loss and circadian disturbances and the “mismatch between crew physical capabilities and task demands.”

Earth Applications

The knowledge we hope to gain from this research, though focused on spaceflight, will also benefit people on Earth. The sleep deficits experienced by astronauts during spaceflight can be considered a threat to the success of space missions (NASA Human Research Program Integrated Research Plan, 2009). The resulting physiological and behavioral changes caused by sleep and circadian disruption can lead to diminished alertness, cognitive ability and psychomotor performance (Dijk et al., 2001). As a measure to counteract sleep disruptions, over 45 percent of all medications taken in space are sleep aids (Putcha et al., 1999).

A significant portion of the global population suffers from chronic sleep loss and/or circadian-related disorders. Evidence for disease or illness occurring due to a disruption of circadian homeostasis has mounted significantly in the past several years. In the United States, nearly 22 million Americans perform shift work that interferes with a biologically healthy nocturnal sleep cycle (U.S. Bureau of Labor Statistics, 2007). Shift workers have been shown to be more likely to suffer from a wide variety of ailments including cardiovascular disease, gastrointestinal distress, and cognitive and emotional problems.

Furthermore, epidemiological studies of female shift workers have shown that they are statistically more likely to suffer from breast and colon cancer as compared to their day-shift counterparts. The World Health Organization has identified shift work as a probable risk for cancer (The International Agency for Research on Cancer, 2007).

Our laboratory is involved in testing the hypothesis that nighttime exposure to light suppresses melatonin and contributes to cancer risk (Blask et al., 2005; Stevens et al., 2007). Aside from evidence of a breakdown in physical health, the effects of circadian disruption and sleep loss are known to have potentially dangerous behavioral effects. Mental fatigue, diminished alertness, loss of psychomotor coordination and decreased physical performance are all commonly found in individuals with sleep loss, sleep debt or circadian misalignment. The impact of these dangers affects many industries, including transportation, manufacturing, communications and medicine. It has long been a source of concern for the military and more recently, homeland security. Many people also experience the same effects after air travel across several time zones. In the past, the U.S. Air Force has supported our laboratory to study the acute alerting effects of light (French et al., 1990; Brainard et al., 1996). Our current work for the National Institute of Health (NIH) has continued this effort (Lockley et al., 2006).

Existing light therapy interventions stand to benefit from enhancing our understanding of how different wavelengths of the spectrum affect human circadian and neurobehavioral regulation. The result may be a more efficient intervention with increased potency and/or fewer side effects. One such disorder currently being treated with bright white light is Seasonal Affective Disorder (SAD), also known as winter depression. It is estimated that as many as one in five Americans suffer from SAD or its milder version, subsyndromal Seasonal Affective Disorder (sSAD) (Lam and Levitt, 1999). Similar bright white light interventions are also used to treat jetlag. Side effects from exposure to bright white light for these and other therapies include: hypomania, headache, vision problems, nausea, dizziness and anxiety. Optimizing the light spectrum for specific affective and/or circadian-related disorders may deliver the same medical benefit with lower levels of light intensity, and potentially fewer side effects. Our group has completed Phase I testing of a lower-intensity of light therapy with blue solid-state lighting for SAD patients (Glickman et al., 2006).