LAUSR

All‐inorganic halide perovskites (CsPbX3, X = Cl−, Br−, and I−) are brought to the forefront of research focus in the field of modern lighting technology. However, due to the toxic element (Pb2+), environmentally friendly white‐light emissions are difficult to achieve, thus limiting their practical applications. Herein, high‐quality Mg2+‐alloyed CsPb1−x Mgx X3 (up to 20%) nanocrystals (NCs) are synthesized. The structural and optical properties are investigated. The application of these NCs in white‐light‐emitting diodes (LEDs) is also demonstrated. The incorporation of Mg2+ into CsPb1−x Mgx X3 NCs results in a lattice contraction without a change in structure and morphology, blue‐shifts in the photoluminescence emission, and increased bandgap. Then, the tunable emission (≈408–650 nm) is obtained by adjusting the compositions of different halides (for 20% Mg2+). Most importantly, for the first time, 3D printed thin color conversion layers for different color emitting NCs (green, yellow, and red) are stacked on top of the blue‐LEDs to achieve high‐quality white light emission. A bright neutral white‐light with a correlated‐color temperature of 5806 K, a high color‐rendering index of 89, CIE coordinates of (0.32, 0.33), a small Duv (<0.003), and high luminous efficacy of radiation of 280 lm W−1 is achieved.