lights-out campaign; annual turning off of lights
Refers to an organized event, often annual, where lights are turned off for energy conservation or environmental awareness. Wasei-eigo from English 'light down'.
wasei-eigo (Japanese-coined English), from light down
This year's lights-out campaign will be held on June 21st.
Let's participate in the lights-out event and turn off the lights.
Wasei-eigo from English 'light down'. The exact origin is uncertain, but it likely emerged in Japanese environmental campaigns.