Influence of light exposure on cesium lead halide nanostructures has been explored. A discovery of photon driven transformation (PDT) in 2D CsPbBr3 nanoplatelets is reported, in which the quantum‐confined few‐monolayer nanoplatelets will convert to bulk phase under very low irradiation intensity (≈20 mW cm−2). Benefiting from the remarkable emission color change during PDT, the multicolor luminescence photopatterns and facile information photo‐encoding are established.