Abstract
Medical community has been sounding alarm with increasing frequency on the health hazards of blue light. It should now be cleared that we need a blue hazard free lighting source that is friendly to human eyes, physiologies, artifacts, ecosystems, environment, and night skies. In response to a positive demand, we demonstrate here a blue hazard free candlelight organic light-emitting diode (OLED) using wet process at least the layers of emission, hole-injection, and hole-transportation. Wet process enables candlelight OLED to be fabricated cost-effectively with large area-size via continuous roll-to-roll manufacturing. From energy-saving perspective, at 100 cd/m2, the resultant wet processed candlelight OLED exhibits the power efficiency of 33.2 lm/W, which is 3 and 300 times higher than incandescent bulb and candle, respectively. Notably, from healthy perspective, the resulting 1,918 K candlelight OLED shows only 1% melatonin suppression sensitivity (MSS), comparing to that of 480 nm blue light. The 1% MSS is about 15 times safer as comparing with the high temperature (5,000K) white light emitting diode (LED), compact fluorescent lamp (CFL), and OLED. When it comes to human eye protection, the candlelight OLED permits an 8 hours exposure limit before causing permanent damage to retina at 100 lx, an average lighting level for home living. Under 500 lx, a typical lighting level in office, the exposure limit becomes 5 times shorter, which is about 1.6 hours. The calculated result of exposure limit is 50 times safer than those of high color temperature white lighting counterparts. This study may serve as a starting point to fuel up a healthy light based “Lighting Renaissance” with high added-value commercialization feasibility. Hence, the candlelight OLED is bound to rewrite the history of mankind lighting and safeguard human health.