10 January/February 2020 | informationdisplay.org Tailoring the Spectrum Low-Cost Perovskite- Polymer Composites A lid-ae lighig becme mae ad ie f me ha aig eeg, he abili  ail he ecm fllig ecic eieme ffe emed iie. Hee, f ah fm he Uiei f Ceal Flida e l-c, ligh- diffig ekie-lme cmie  mee demad. WITH ITS LOWER POWER CONSUMPTION, LONGER LIFE- tme, smaller size, higher brightness, and faster response tme, solid-state lightng (SSL) based on white LEDs has gradually overtaken incandescent and fuorescent lightng sources in the last few decades.1 Although researchers have devoted signifcant efort to improving its efciency, they've also studied the biolog- ical impact of light on human beings, plants, and animals.2,3 Now is the tme for SSL manufacturers to aim beyond energy savings, and expand their focus to applicatons such as circadian or hort- cultural lightng. In that sense, tailoring the spectrum according to specifc requirements will become increasingly crucial, as it will maximize the efectveness of the lightng by ensuring the presence of necessary spectrum components and, in the mean- tme, reduce or omit unnecessary or even damaging portons of the spectrum. For instance, under ambient light, the intrinsically photosensitve retnal ganglion cells (ipRGCs) innervatng the suprachiasmatc nucleus (SCN) can infuence melatonin secre- ton, thereby afectng the circadian rhythm.4 In reference to the experiments on light-induced melatonin suppression, Dietrich Gall proposed an "acton spectrum" of the circadian efect, with a peak at blue wavelengths.5 (Incidentally, an “acton spectrum” means a response spectrum correlated to the circadian efect, in this case with a peak around 460 nanometers [nm].) Indeed, it is necessary to factor the circadian efect into future design consideratons to achieve human circadian lightng. by Ziqian He, Caicai Zhang, Yajie Dong, and Shin-Tson Wu With this in mind, here we examine current SSL solutons and, based on the tailored SSL requirements, we propose low-cost, light-difusing perovskite-polymer composites as candidates for narrow-band, color-tunable emiters. Using spectral optmiza- tons, we ofer a circadian SSL soluton with high efciency and excellent color rendering by incorporatng perovskite-polymer composites. What SSL Currently Ofers Current SSL solutons can be roughly categorized into three classes. Phosphor-converted white LEDs (pc-WLEDs) are the frst and most mainstream soluton. The simple design and low cost make them ideal for general, statc lightng. However, the phosphor’s broad spectral power distributon (SPD) is considered spectrally inefcient, because human eyes are most sensitve to green light with a peak at 555 nm (photopic vision), and the broad SPD causes a signifcant spillover of light into the deeper red where human vision is not very sensitve. Meanwhile, as SSL becomes smarter, it requires SPD dynamic tuning. 6,7 Although some existng proposals can tune the SPD of pc-WLEDs (by using, for example, an actve color flter), 8,9 it is stll energy-inefcient, with a rather limited SPD engineering degree of freedom. An additonal problem with pc-WLEDs is that they use an FRONTLINE TECHNOLOGY