history
The first four characters 火树银花 come from Su Weidao 苏味道 's Tang poem 《正月十五夜》: 火树银花合, 星桥铁锁开, describing Lantern Festival lights. 不夜天 (a sky that knows no night) was later fused with it, and the full phrase was popularised in modern stage works and song.
usage
Often used in festival reporting (Spring Festival, National Day, Lantern Festival). 火树 = trees of fire (lanterns and fireworks), 银花 = silver blossoms (sparks).
