In 2012, the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute published a study that changed the way we think about using “self-luminous devices” such as tablets, laptops and e-readers at night. The study led by Professor Mariana Figueiro, Light & Health program director at the LRC, found that light from tablets can affect evening melatonin and, therefore, may delay sleep. The research results were widely covered by the news media, with stories appearing in The New York Times, Los Angeles Times, New York Daily News, The Washington Post, Huffington Post, Scientific American, The Economist, and other major news organizations around the world.

Figueiro conducted a follow-up study and has published a new paper, titled, “Self-luminous devices and melatonin suppression in adolescents,” in the journal, Lighting Research & Technology. The new study was the first to be conducted in the home environment that investigated the effects of self-luminous devices on melatonin levels in adolescents. Results show that 1-hour exposure to light from self-luminous devices suppressed melatonin by approximately 23 percent, and 2-hour exposure suppressed melatonin by approximately 38 percent.

While the measured light exposure was about the same, the melatonin suppression was higher than what was observed in the 2012 study, which suggests that adolescents are more sensitive than adults to light from self-luminous devices. Melatonin suppression can negatively impact an individual’s ability to fall asleep by delaying the timing of sleep onset.

“One of the most striking findings from the present study was that adolescents seem to have a heightened sensitivity to evening light for acute melatonin suppression,” said Figueiro. “Although the light levels were similar, the amount of suppression observed in the present study was much higher than that observed in adults in previous studies conducted at the LRC.”

For the new study, 20 adolescents (aged 15-17 years) viewed self-luminous devices through orange-tinted glasses that filter out short-wavelength light, and then viewed the same self-luminous devices without orange-tinted glasses. The orange-tinted glasses served as a “dark” control condition since they remove short-wavelength light that suppresses melatonin production. Each participant also wore a Daysimeter—a calibrated, personal light and activity sensor developed by the LRC—to measure circadian light and quantify circadian entrainment or disruption. The participants were allowed to use computers, tablets, e-readers, televisions, and mobile phones.

Self-luminous devices, such as those used in this study, can emit short-wavelength (blue) light, which maximally suppresses melatonin. Exposure to this light in the evening and at night may lead to acute suppression and delay the timing of melatonin production, both of which are believed to be detrimental to sleep quantity and quality.

“If we want to have a good night of sleep, we should keep a regular schedule, increase the amount of circadian light exposure during the daytime hours, and reduce it during the evening hours,” said Figueiro. “Try to limit the use of self-luminous devices two hours prior to bedtime. If that is not possible, dim down the screen brightness, or filter out the short-wavelength light by adding theatrical gels to the device, or by wearing orange-tinted glasses. These simple actions may result in earlier bedtimes that could help improve mood, wellbeing, and perhaps even school performance.”

About the Lighting Research Center
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is the world's leading center for lighting research and education. Established in 1988 by the New York State Energy Research and Development Authority (NYSERDA), the LRC has been pioneering research in energy and the environment, light and health, transportation lighting and safety, and solid-state lighting for more than 25 years. In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today the LRC offers both a M.S. in lighting as well as a Ph.D. to educate future leaders in lighting. Internationally recognized as the preeminent source for objective information on all aspects of lighting technology and application, LRC researchers conduct independent, third-party testing of lighting products in the LRC's state of the art photometric laboratories, the only university lighting laboratories accredited by the National Voluntary Laboratory Accreditation Program (NVLAP Lab Code: 200480-0). LRC researchers are continuously working to develop new and better ways to measure the value of light and lighting systems, such as the effect of light on human health, and the effect of light on plant physiology.
The LRC believes that by accurately matching the lighting technology and application to the needs of the end user, it is possible to design lighting that benefits both society and the environment.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The university offers bachelor's, master's, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.