The study was conducted by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, and was led by Mariana Figueiro, associate professor at Rensselaer and director of the LRC's Light and Health Program.
In order to examine the impact of self-luminous tablets on melatonin suppression, the researchers enrolled 13 people who used self-luminous tablets to read, watch movies, and play games.
"Our study shows that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22%. Stimulating the human circadian system to this level may affect sleep in those using devices prior to bedtime."
According to the researchers, the actual melatonin suppression values after 60 minutes were comparable to the values estimated using a predictive model of human circadian phototransduction for 60 minutes light exposures. Figueiro, said: "Based on these results, display manufacturers can use our model to determine how their products could affect circadian system regulation."
The teams findings could urge manufacturers to develop more "circadian-friendly" electronic devices that could either increase or decrease circadian stimulation depending on the time of day.
In addition, manufacturers may be able to use data and predictive models in the future to develop tablets for tailored daytime light exposures that reduce symptoms of seasonal affective disorder, and sleep disorders in the elderly.
LRC Research Specialist Brittany Wood, said:
"Technology developments have led to bigger and brighter televisions, computer screens, and cell phones. To produce white light, these electronic devices must emit light at short wavelengths, which makes them potential sources for suppressing or delaying the onset of melatonin in the evening, reducing sleep duration and disrupting sleep. This is particularly worrisome in populations such as young adults and adolescents, who already tend to be night owls."
The researchers assigned study participants to one of three groups:
- Participant in the first group viewed their devices through a pair of clear goggles fitted with 470-nm (blue) light from light emitting diodes (LEDs).
- Those in the second group viewed their tablets through orange-tinted glasses, capable of filtering out the short-wavelength radiation that can suppress melatonins.
- Participants in the third group did not wear glasses or goggles.
The Dimesimeter device, developed by the LRC, continuously records circadian light and activity levels.
The team found that participants melatonin levels were affected by the duration of exposure and the distance between the eye and the display. After 60 minutes, melatonin suppression was not significantly affected, but there was significant suppression after a 2-hour exposure.
In addition, the team found that the type of task being performed on the tablets also determines how much light is delivered to the cornea, thus, affecting evening melatonin levels.
The researchers found that the range of photopic illuminance levels at the cornea from the tablets alone varied from 5 lux, which is not likely to impact melatonin, to over 50 lux, which would significantly reduce melatonin after 2-hours.
Until more "circadian-friendly" devices are developed, Figuerio has several recommendations to reduce their effects on sleep. "We recommend dimming these devices at night as much as possible in order to minimize melatonin suppression, and limiting the amount of time spent using these devices prior to bedtime."
Written by Grace Rattue