绿灯
lǜ dēng · HSK 7
green light
🟢 绿灯 = 绿 (green) + 灯 (lamp/light) = the green light at a crossing
绿 means green and 灯 means lamp or light, so 绿灯 is literally a green lamp. Beyond traffic, 开绿灯 (open a green light) is a set phrase meaning to give approval or the go-ahead for something.
绿 — silk radical 纟 + 录 (phonetic)
绿 is a phono-semantic compound. The silk radical 纟 (糸) signals the original sense of a dyed silk color, while 录 supplies the sound. It came to mean the green color produced by such dyes, and now refers to green in general.
灯 — fire radical 火 + ding 丁 (phonetic)
灯 is a semantic-phonetic compound: 火 'fire' gives the meaning (lamps once burned oil or flame), while 丁 hints at the sound. It is the simplified form of the traditional 燈, which used 登 as the phonetic. Today it means 'lamp' or 'light'.