Halide perovskites have garnered attention because they’re highly efficient at capturing energy in solar cells and efficient emitters in diodes. But researchers failed at making perovskite LEDs that emit blue light. Chemists succeeded, but X-ray studies of the LED’s structure show that it’s very sensitive to temperature, humidity and chemical environment. Hence environmental and chemical control is essential for stable operation. But these properties also allow for potentially broader use, such as sensors.