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Characteristics of Light Exposure Necessary for Development of Optimal Countermeasures to Facilitate Circadian Adaptation and Enhance Alertness and Cognitive Performance in Space

Principal Investigator:
Steven W. Lockley, Ph.D.

Harvard - Brigham and Women's Hospital

During missions, the quickly changing light-dark cycles that astronauts experience in orbit affect the body’s natural circadian cycle, causing disturbed sleep and difficulty waking. Noise, the effects of microgravity and temperature can further exacerbate sleep problems, potentially resulting in cognitive deficits and fatigue-related accidents. Dr. Steven W. Lockley and colleagues are investigating the effectiveness of short-wavelength blue light exposure to phase-shift the circadian pacemaker, suppress melatonin and directly enhance alertness. The team is working to answer questions regarding the specific characteristics of the body’s sensitivity to blue light, and to test whether time of day or light intensity affect these light responses.

NASA Taskbook Entry

Technical Summary

Space missions often expose crew members to unusual light-dark cycles that lead to misalignment between the circadian pacemaker and the sleep-wake schedule, resulting in disturbed sleep and impaired waking function. Sleep disturbances due to other reasons (e.g., noise, temperature, microgravity) further exacerbate cognitive deficits, and these factors jointly increase the risk of fatigue-related accidents and injuries. An effective countermeasure is required to facilitate more rapid adaptation of the circadian system and directly enhance alertness and performance. Light exposure induces both of these effects and is an effective, safe, non-pharmacological countermeasure for circadian- and fatigue-related deficits in cognition.

Recently, we and others have shown that short-wavelength (blue) light exposure at night is the most effective wavelength for phase-shifting the circadian pacemaker, suppressing pineal melatonin, enhancing subjective alertness, improving performance and inducing EEG-derived brain activation that indicates a more alert state. These effects, however, have only been examined during the night using relatively bright light, and recent evidence suggests that the spectral sensitivity of the circadian photoreception system may depend on the intensity and duration of light and that there may be changes in spectral sensitivity during the day. While blue light therapy to facilitate circadian adaptation and alertness has been proposed based largely on the effects of melatonin suppression at night, these data may not be transferable to the effects at other times of day (when melatonin is not produced) or for other effects of light. Before blue light is operationalized, three fundamental questions remain to be determined:
  1. Does the spectral sensitivity depend on the intensity of light?
  2. Do all non-visual effects of light have the same spectral sensitivity?
  3. Is the spectral sensitivity of the circadian photoreception system different between the day and the night?
Failure to address these questions may result in deployment of suboptimal or less energy-efficient lighting schedules. This project will test whether the spectral sensitivity of the circadian photoreception system is intensity-dependent, response-dependent or time-of-day dependent, by comparing the effects of exposure to monochromatic light during the day and the night, at both high and low intensities, on circadian phase resetting and enhancement of alertness and performance.

Experiment 1 aims to compare the melatonin suppression, phase resetting and alerting effects of exposure to dim 460 nm and 555 nm monochromatic light exposure at night, and compare these data to previously collected findings for bright light exposure at night using the same protocol. Data collection for Experiment 1 is complete, and analysis is complete for the results for phase shifting, melatonin suppression, subjective alertness and psychomotor performance. Waking EEG data are still under review. Experiment 2 will test the effects of exposure to bright 460 nm and 555 nm monochromatic light during the daytime and is ongoing, with data collection due for completion by the end of 2010. Experiment 3 aims to test the effects of exposure to dim 460 nm and 555 nm monochromatic light during the daytime and will begin in the fall of 2010.


Earth Applications

The purpose of the proposed studies was to test three specific hypotheses aimed at evaluating the spectral and temporal sensitivity of light to reset the circadian pacemaker, and acutely improve alertness and performance during both daytime and nighttime exposures. These studies are designed to provide fundamental information about the photoreceptor systems that detect light for a range of circadian, neuroendocrine and neurobehavioral responses to light in order that optimal lighting can be designed to alleviate circadian misalignment, and acutely improve alertness during space exploration missions.

Although the primary goal of the project is to develop lighting countermeasures for the space environment, the project also has important implications for Earth-based applications including light therapy for treatment of circadian rhythm disorders (advanced and delayed sleep phase syndromes, shift-work disorder and jet-lag disorder). Another application is the use of light as a non-pharmaceutical fatigue countermeasure in many other settings where high-alertness and performance is paramount, such as military personnel, first-responders (police, firefighters, paramedics), and other safety-sensitive professions (e.g., pilots, physicians, nurses, truck drivers).

Our work has already begun to influence architectural lighting design with the development of methods both by ourselves and others to incorporate the non-visual effects of light into design of ‘healthy’ buildings aimed at reinforcing robust circadian entrainment through light-dark cycles, and the potential of light to enhance workplace performance and alertness. Dr. Lockley is also a member of several national and international committees tasked with developing new lighting standards for the non-visual effects of light, which will be informed by the current project and will ultimately be used by industries worldwide to develop lighting and lighting practices that optimize both the visual and non-visual effects of light.


This project's funding ended in 2011