影 pairs 景 (a sunny scene: sun 日 over a capital 京) with 彡, three flowing strokes that paint streaks. Bright light plus streaks = the shadow it throws. The character literally draws light and its dark twin together.
影 gives Chinese its most poetic tech word: 电影 (electric shadow — the movies). Shadow-play 皮影戏, the ancient leather-puppet cinema, entertained China a thousand years before film arrived, so when projectors came, 'electric shadows' felt exactly right. 影子 is your everyday shadow; 合影 is a group photo — capturing everyone's image at once.
A bright scene 景 + streaks 彡 = the SHADOW that light paints.
Shadow puppetry (皮影戏) is a 2,000-year-old 'cinema' — UNESCO lists it as intangible cultural heritage.