Effect of organic light-emitting diode on nighttime task performance and melatonin secretion: Randomized controlled trials

This study aimed to determine whether organic light-emitting diode (OLED) lighting with low intensity and color temperature (150 lux, 3000 K) maintains nighttime task performance and reduces melatonin suppression compared with a generally used LED lighting with high intensity and color temperature (750 lux, 5000 K). We conducted two randomized crossover trials. Study 1 included 39 adults who answered the Uchida–Kraepelin test (UKT) within 2 h under the OLED and LED conditions; Study 2 included 30 men whose salivary melatonin levels were measured in 5-h exposure to the aforementioned conditions. The mean number of UKT answers and errors, melatonin suppression, and changes in melatonin levels from the baseline were compared between the two conditions. No significant differences were observed in the mean number of UKT answers and errors between the OLED and LED conditions. Noninferiority analysis revealed that the OLED lighting was not inferior to the LED lighting in terms of the mean number of answers (LED: mean, 835.7; noninferiority margin, 116.2; OLED: 95% confidence interval, 745.3–902.4). Furthermore, OLED reduced the overall melatonin suppression by 56.1% compared with LED. Similarly, multilevel analysis revealed significantly lower reduction in salivary melatonin, by 5.7 pg/mL, in OLED than in LED. In conclusion, we demonstrated that melatonin suppression was significantly reduced without reducing nighttime task performance in the OLED lighting condition compared with generally used LED lighting condition. Further studies, including comparisons between OLED lighting and LED lighting under the same conditions, are warranted to better understand the effect of OLED on nighttime task performance and melatonin suppression.