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Optimizing Light Spectrum for Long-Duration Spaceflight

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

Jefferson Medical College of Thomas Jefferson University

Disturbed sleep-wake patterns that occur during space missions result in decreased alertness and concentration, compromising the performance and safety of astronauts and NASA ground control workers. Studies show that light treatment can correct similar impairments that occur with shift work, jet lag and sleep disorders. Dr. George C. Brainard is determining the best wavelengths of light to use during long-duration spaceflight to readjust biological rhythms and sleep patterns in astronauts. Based on earlier studies, Brainard will determine whether blue-enriched fluorescent light can be used to regulate circadian rhythm in the low-lighting levels common to space craft. If successful, then onboard artificial lighting systems may serve the dual purpose of maintaining circadian entrainment while providing illumination that supports vision. These data also may be used to improve space suit visors and windows used in space vehicles and habitats, and to design ideal lighting for astronauts and mission control workers during long-duration space exploration.

NASA Taskbook Entry

Technical Summary

The goal of this project is to determine the optimal wavelengths of light for use as a countermeasure to sleep and circadian disruption for astronauts. Sleep deficits are a risk factor during space missions. The resulting physiological and behavioral changes from sleep and circadian disruption can threaten the success of a mission by diminishing alertness, cognitive ability and psychomotor performance. Currently, over 45 percent of all medications taken in space are sleep aids.

Ambient light is the primary stimulus for human circadian regulation. While on Earth, humans have a 24-hour day/night cycle to maintain healthy circadian entrainment. In space, astronauts must contend with either a rapidly changing or severely disrupted day/night cycle, and must work in a dimly lit spacecraft interior with few or no windows. Bright white light has already 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), the planned Crew Exploration Vehicle (CEV) and future lunar habitats raises several concerns, among which are heat production, energy consumption and upmass. Mitigating these factors requires a better understanding of how different wavelengths of light regulate the human circadian system. From this data, it may be possible to optimize the light spectrum both as a countermeasure for sleep and for circadian disturbances before or during space exploration. Listed below are the specific aims of this project. Given changes in NASA priorities.

Specific Aims

  1. Test the hypothesis that the white polychromatic fluorescent lamps currently used by NASA as a pre-launch countermeasure for circadian and sleep disruption will have increased efficacy for melatonin suppression when they are enriched in the blue portion of the spectrum. Our published action spectrum indicates that the blue monochromatic wavelengths (446-477 nm) are the most potent for melatonin suppression. This aim was intended to determine if increasing the power in the blue region of a polychromatic fluorescent light can increase potency for melatonin suppression while keeping the visual experience white. Philips Lighting B.V., an NSBRI industry partner, donated the prototype blue-enriched lamps and exposure systems used in this study. Since the start of the project, 25 human subjects have completed a total of 248 nighttime melatonin suppression trials. The data are now being analyzed for publication.

  2. Test the hypothesis that the white polychromatic fluorescent lamps currently used by NASA as a pre-launch countermeasure for circadian and sleep disruption have increased efficacy for circadian phase-shifting when they are enriched in the blue part of the spectrum. For this aim, we are comparing the magnitude of circadian phase-shifts in healthy subjects following exposure to equal photon densities of blue-enriched fluorescent lights versus the white lamps currently used by NASA. Each subject goes through a seven day, 24 hour a day, inpatient trial with assessment of multiple biological and behavioral endpoints. A total of 21 subjects have been entered into the protocol and of these, 20 completed the full study. Assay of blood samples and assessment of behavioral data is ongoing for this study. Enrollment has not been closed.

  3. Test the hypothesis that three ambient extraterrestrial light environments (sky light during low Earth orbit for ISS and the CEV, ambient light on the lunar surface and ambient light on the surface of Mars) differ in their capacity to regulate melatonin. Since circadian and sleep regulation depends on an astronauts total exposure to both artificial and passive ambient illumination through windows or spacesuit visors, it is essential to determine the circadian effects of non-terrestrial light exposures. To test this hypothesis, we are working collaboratively with investigators from the Lunar and Planetary Laboratory of the University of Arizona who are experts in characterizing the light in a variety of extraterrestrial environments. Although progress was delayed by almost two years due to unforeseen optical design problems, a functional optical array was developed to establish melatonin suppression responses with polychromatic light that simulates light in low Earth orbit, ambient light on the lunar surface and ambient light on the surface of Mars. The first prototype of this optical system was delivered to our lab in March 2007. Since then, nine human subjects have completed more than 80 nighttime melatonin suppression trials with simulated lunar light, and nine other subjects have completed more than 60 nighttime trials with simulated Martian light. Running of subjects, assay of blood samples and data analysis is ongoing.

In 2008, this project was competitively renewed for an additional four years through an NSBRI research solicitation. Some work on elements from the previous four years will be continued. Specifically we plan to submit a manuscript for peer review on all of the data from Aim 1, complete the phase-shift study in Aim 2, and complete the fluence-response curves with simulated lunar light and Mars light in Aim 3.

Ultimately, these data will impact NASA lighting requirements and improve light treatment used as a countermeasure for circadian and sleep-wake disruption in space exploration. The data will also help NASA identify the best spectral transmission for spacesuit visors, space vehicles and habitat windows, and the ideal spectral distribution for illumination of living quarters.

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 (Longnecker and Molins, 2005). 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 do shift work that interferes with a biologically healthy nocturnal sleep cycle (US 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 have long been 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 Institutes of Health 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 impact with lower levels of light intensity and potentially fewer side effects. Our group has completed Phase I testing of light therapy with blue solid-state lighting for SAD patients (Glickman et al., 2006).

This project's funding ended in 2008