Blue‐Light‐Free Orange‐Red Organic Light‐Emitting Diodes With Less Influence on Melatonin Secretion

The night lighting in the hospitals is now a major cause of sleep disorder for the patients. The predominant light-emitting diode (LED) contains a sharp blue peak, which is known to reduce the natural melatonin secretion in the brain. Melatonin level is crucial to the biological clock. Organic LED (OLED) has a blue-free and broad spectrum. The conventional vacuum process is however too expensive. Here the lifetime of solution-processed OLED is significantly improved by the selection of multiple host materials in the emission layer, the removal of the interfaces, and the prevention of the point defect over large areas. OLED panels with a 3 cm × 4 cm emission area with continuously tuned color are made over 20 cm by 29 cm glass substrate by cylindrical blade coating. The lifetime is raised to 820 h. The orange-red OLED panels are applied in a sleep clinical study with 24 cases. White LEDs with and without color filters were also studied for comparison. At the same illumination of 30 lux, OLED is shown to have less effect on the melatonin level than white LED with or without color filter. This implies that OLEDs can help alleviate sleep disorders.