In our 24-hour global society, now more than ever workers and business travelers need to be alert at night or under different time zones. Past research of light’s effect on human circadian rhythms shows that the body’s “master clock” is strongly influenced by the 24-hour cycle of light and dark. By the same token, nocturnal light exposure of a certain spectrum, intensity, and duration can increase both objective and subjective measures of alertness. As a result, lighting designs that achieve the objectives of alertness and circadian regulation would be a boon to those who find themselves out of sync with the standard sleep/wake routine or the local time zone.
Not enough conclusive information is available just yet to develop lighting specifications that achieve these objectives; however, recent research from the Lighting Research Center is helping the lighting community get closer.
A new study published by LRC scientists shows a strong, positive correlation between model predictions of light-induced melatonin suppression and measures of nocturnal alertness. Lead author Mariana Figueiro, Ph.D., of the LRC said, “We already know that light exposure at night, including blue light, increases alertness and influences circadian regulation, particularly the suppression of the melatonin hormone. But we haven’t known until now that the phototransduction mechanisms in the retina that provide input to the suprachiasmatic nuclei, or SCN, in the brain for nocturnal melatonin suppression are the same as those providing input for nocturnal alertness. Therefore, we now know that the SCN play an important role for both light-induced nocturnal melatonin suppression and alertness.”
The importance of this relationship between mechanisms for melatonin suppression and alertness stems from the need for a model that can predict the effects of light stimuli for any spectrum and intensity—a requirement for the development of circadian-based lighting specifications, said Dr. Figueiro. Two years ago, LRC scientists published a model for human circadian phototransduction that can be used to predict the effectiveness of different light sources for suppressing melatonin production at night (see the October 2005 LRC newsletter for details). The hormone melatonin levels seem to be critical to synchronizing the body’s circadian responses, such as the sleep/wake cycle and core body temperature, as well as cell division and repair. Figueiro said that the purpose of this new study was to determine whether the same model for light’s effect on nocturnal melatonin suppression could also be applied to light’s effect on nocturnal alertness.
Study subjects stayed awake from midnight to 8:30 a.m. and were exposed to four intensity levels of narrowband blue light (peak at 470 nm) during several sessions of 50 minutes each. Researchers recorded electroencephalographic (EEG) data related to alertness after each light-exposure session, followed by a survey regarding the subjects’ perceptions of how drowsy or alert they were feeling. In comparisons of these two types of data, results showed that the relationship between light exposure and the subjective measure of alertness (the survey) converged with that between light exposure and the objective measure of alertness (the EEG data). When researchers plotted the measured objective data against model predictions of nocturnal melatonin suppression for the same light exposures, they also found a strong correlation.
“By finding this correlation between nighttime alertness and the existing prediction model for melatonin suppression, we can now make a priori predictions that will help with developing future specifications for using light to improve alertness at night,” said Figueiro.
One situation where improved alertness is desirable is transcontinental flight. Jet-lagged business travelers often arrive at their destinations on a red-eye flight not having slept much or experienced a sufficient light/dark cycle. Commercial airplane manufacturers are now using LED technology to create dynamic “mood lighting” that simulates the cycles of day and night, with the goal of helping passengers feel better during a long-haul trip. Such lighting designs are being integrated into new airplanes, such as Boeing’s 787 Dreamliner, scheduled to enter service in 2008. The LRC recently collaborated with Boeing on projects to evaluate current aircraft interior lighting designs and to specify new lighting concepts and requirements (see the April 2005 newsletter for details on the LRC-Boeing partnership).
The nocturnal alertness study published by Figueiro, John D. Bullough, Andrew Bierman, Charles R. Fay, and Mark S. Rea, “On light as an alerting stimulus at night,” was published in the journal Acta Neurobiologiae Experimentalis, volume 67, number 2, and is available on the journal’s Web site.
|About the Lighting Research Center|
The Lighting Research Center (LRC) is part of Rensselaer Polytechnic Institute of Troy, N.Y., and is the leading university-based research center devoted to lighting. The LRC offers the world's premier graduate education in lighting, including one- and two-year master's programs and a Ph.D. program. Since 1988 the LRC has built an international reputation as a reliable source for objective information about lighting technologies, applications, and products. The LRC also provides training programs for government agencies, utilities, contractors, lighting designers, and other lighting professionals. Visit http://www.lrc.rpi.edu.