The use of computers, including devices such as smartphones, tablet computers and laptops before bed has been associated with a reduction in the hours of sleep experienced by frequent users, along with a decreased quality of sleep, in most cases. The results of computer use at night have been linked with tiredness. A study carried out by the University of Oxford shows that in 73% of cases, smartphone usage led to people being more tired. However, in 27% of cases there was no change.
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Sleep needs
An adult is expected to sleep 7–9 hours per night to be properly rested, while adolescents from the age of 10-17 need 8.5-9.5 hours of sleep, with the hours needed decreasing with increased age. Failing to meet these sleep needs has been linked with depression, obesity, diabetes, and cardiovascular disease. An important factor in sleep is melatonin, a hormone produced in the pineal gland that is associated with sleep facilitation. During the daytime, blood melatonin levels are barely detectable, but at night, melatonin levels are high. This phenomenon is due to light's effect on melatonin production. If there is sufficient light, then melatonin production is halted. It is possible for artificial light to be bright enough to have this effect.
Video games
In a 2012 study, "The impact of prolonged violent video-gaming on adolescent sleep: an experimental study", 17 adolescents were told to play a violent video game before going to bed. They were split into groups with 50 minutes or 150 minutes of game play. There was no discernible difference in heart rate during game play and after. However, the group of longer game video game play sessions experienced both a lowering in the quantity and the quality of sleep. In the case of sleep quality, participants experienced a loss of REM sleep, or rapid eye movement sleep, important for encoding new information from short term to long term memories. This study however did not link the sleep reduction experienced to physical arousal, which in this study was measured through heart rate. A 2010 study, "Electronic media use and sleep in school-aged children and adolescents: a review", took 36 published papers and attempted to find links between electronic use and sleep loss. Through the meta analysis of the studies, the study hoped to be able to better pinpoint the cause of sleep loss, in order to establish causation(s) rather than simply correlation. Electronics involved included televisions, computers, electronic games, internet devices, cell phones, and music devices. Although the study was unable to make definitive conclusions about the cause of sleep loss, it provided evidence that electronics use before bed had a negative impact on sleep. Media overuse has been the most strongly associated with sleep loss. The mere presence of electronics in the room during sleep has also been shown to negatively impact sleep.
Mobile devices
A 2012 study, "Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression", showed that melatonin levels are suppressed by roughly 22% when someone is exposed to backlit screens for two hours. This drop is similar to what one would expect after being exposed to normal sunlight. Exposure to backlit screens for only one hour rather than two hours showed no significant melatonin suppression.