In response to the call for a physiologically-friendly light at night that shows low color temperature, a candle light-style organic light emitting diode (OLED) is developed with a color temperature as low as 1900 K, a color rendering index (CRI) as high as 93, and an effi cacy at least two times that of incandescent bulbs. In addition, the device has a 80% resemblance in luminance spectrum to that of a candle. Most importantly, the sensationally warm candle light-style emission is driven by electricity in lieu of the energywasting and greenhouse gas emitting hydrocarbon-burning candles invented 5000 years ago. This candle light-style OLED may serve as a safe measure for illumination at night. Moreover, it has a high color rendering index with a decent effi ciency.

Yellow emission is crucial in RGBY display technology and in fabricating physiologically friendly, low color‐temperature lighting sources. Emitters with both wet‐ and dry‐process feasibility are highly desirable to fabricate, respectively, high‐quality devices via vapor deposition and cost‐effective, large‐area devices via roll‐to‐roll fabrication. Here, high‐efficiency organic light‐emitting diodes with a novel wet‐ and dry‐process feasible yellow‐emitting iridium complex, bis[5‐methyl‐7‐fluoro‐5H‐benzo(c)(1,5) naphthyridin‐6‐one]iridium (picolinate), are demonstrated. By spin coating, the device shows, at 1000 cd m−2, an external quantum efficiency (EQE) of 18.5% with an efficacy of 52.3 lm W−1, the highest among all reported yellow devices via wet‐process, while using vapor deposition, the EQE is 22.6% with a 75.1 lm W−1 efficacy, the highest among all dry‐processed counterparts. The high efficiency may be attributed to the replacement of the hydrogen atom with a fluorine atom on a 2‐substitutional site in the emitter to prevent dense molecular packing‐caused self‐quenching and to reduce radiationless deactivation rates, leading to a high quantum yield (71%).

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We demonstrate the feasibility of bringing the sunset hue indoors via a dusk-light-style organic light emitting diode that exhibits a color temperature ranging between 1500 and 3000 K, covering that of sunset hue within the last 30 min before sunset. Like the sunset, the device chromaticity changes from yellowish white to reddish orange, with illuminance decreasing by 60-fold as the color temperature decreases from 2900 to 2100 K. The artificial dusk hue at 2745 K, for example, shows a 92 color rendering index with an 87% luminance spectrum resemblance with the sunset hue. The very high color rendering character is obtained by depositing phosphorescent red and yellow dyes in one emission layer and a fluorescent green dye doped into a fluorescent blue light emitting host in another, separated by a nanoscale carrier modulation interlayer to harvest the ultimate color rendering index and minimize the color temperature.

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