While the action of turning off a light is universal, the phrase 关灯 (guān dēng) is frequently tied to the cultural value of thriftiness and saving resources (节约 - jiéyuē). It's very common for parents to remind their children “随手关灯 (suí shǒu guān dēng)“—”turn off the lights when you leave a room.” This isn't just about saving money on the electricity bill; it's often framed as a good habit and a responsible behavior for the collective good. In the West, reminders to turn off lights are common, but they are often framed around environmentalism (“save the planet”) or personal cost-saving. In China, while these reasons also exist, the act is often linked to a more traditional virtue of not being wasteful (不浪费 - bù làngfèi). Public service announcements and school campaigns often promote slogans like “节约用电,请随手关灯” (Save electricity, please turn off lights when you leave). This makes 关灯 more than just a simple action; it's a small, daily reflection of a widely held cultural value.
关灯 (guān dēng) is a high-frequency, practical term used in all informal and most formal situations.