Melatonin is a hormone produced by the pineal gland. It is released into the body to signal rest and get ready for sleep when the eyes sense indication of darkness. It plays a significant role in regulating circadian rhythms (Soriento, 2010).
Cajochen, Frey, Anders, Späti, Bues, Pross, Mager, Wirz-Justice and Stefani (2011) studied the effects of evening exposure to a light-emitting diodes (LED)-backlit computer screen on circadian physiology and cognitive performance. Their results showed that 5-h evening exposure to white LED-backlit computer screen as compared to the non-LED condition significantly suppressed the melatonin levels and increased alertness. As a result, sustained attention and declarative memory performance were enhanced. This study affirms that human circadian physiology and alertness levels are specifically sensitive to short-wavelength light as corresponding to previous studies. Cajochen et al. proposed that impediment in the melatonin progression could have induced circadian phase shift as the circadian pacemaker received a longer “day” signal. Although the direction of the above study is not parallel with the present study, the effects of evening light exposure on the circadian system are one of the areas the present study sought to find out.
Another research has also been carried out by Figueiro, Wood, Plitnick and Rea (2011) to study the impacts of light from computer monitors on melatonin levels. The impact of luminous cathode ray tube (CRT) computer monitors on melatonin suppression in college students was investigated. Based on the predictions from the model of human circadian photo transduction, computer monitors at the calibrated corneal illuminance level were expected to have no effect on melatonin secretion. Three test conditions were applied where the participants view the computer monitor with bare eyes or through goggles with 40 lux blue light or orange-tinted safety glasses. As compare to the dark control condition and computer monitors only condition whereby there was only insignificant reduction in melatonin level, melatonin levels after exposure to the blue-light goggle experimental condition were remarkably reduced. The targeted population of the mentioned study and present study are of younger generations. The objective of both study is slightly different but effects of self-luminous devices are investigated.
Komada, Aoki, Gohshi, Ichioka and Shibata (2015) examined the effect of exposure to different types of television displays at habitual bedtime on human melatonin and cortisol secretion. The participants were exposed to four different luminance- and wavelength-controlled television displays which were normal luminance, high luminance, normal blue light or half blue light. Salivary melatonin and cortisol levels were measured before and after television viewing. Their findings showed that cortisol secretion was not altered by the different displays. However, melatonin concentrations were notably reduced following exposure to the normal blue light display compared to the half-blue light display. The present study corresponds to the above study in terms of investigating the effects of controlled wavelength. It takes into consideration whether the participants
This study carried out by Figueiro and Overington (2015) carried on from previous studies showing that blue light lowers melatonin concentrations and postpones circadian pacemaker phase. This study which was conducted in home environment investigated the impacts of self-luminous devices on melatonin levels in adolescents. The participants were required to wear orange-tinted glasses when viewing their devices and the period of viewing their devices the following day through the safety glasses were reduced. They present that 1 or 2 hours usage of self-luminous devices in the evening can reduce melatonin concentrations in adolescents. Their findings are consistent with previous studies. Melatonin levels were significantly suppressed to about 23% and 38%. The results manifest that adolescents are highly sensitive to melatonin suppressing evening light. The direction of this study is parallel to the present study as our objective and sample group are similar. The present study desired to identify whether blue light prior sleep affects ones’ sleepiness and delay habitual sleep time.
A research was conducted to compare the effects of two hours of evening reading on a self-luminous tablet on sleep as compare to reading a physical book after daytime bright light exposure by Rångtell, Ekstrand, Rapp, Lagermalm, Liethof, Búcaro, Lingfors, Broman, Schiöth and Benedict (2016). A daytime condition was set by exposing the participants to roughly 564 lux constant bright light for 6.5 hours. Subsequently, the participants read a novel either on a tablet or as physical book for two hours. Salivary melatonin concentrations in the evening were constantly measured. In second experimental condition, they continued to read the same novel during both conditions. Results show that there were no differences in the saliva melatonin levels between the tablet reading and physical book reading conditions. The findings do not correspond to any previous researches that investigates the relationship between evening blue light exposure and melatonin levels. This study and present study both aimed to looked at the effect of evening exposure to blue light on sleep. However, the present study does not give attention to the daytime exposure.