I’ve noticed the lights in the Bank of Montreal building flickering and switching off in odd patterns at night

Dear Urban Decoder: I’ve noticed the lights in the Bank of Montreal building flickering and switching off in odd patterns at night. Is it the work of some crazed janitor?—Brooke Desmond, The Beach

What you witnessed is First Canadian Place’s high-tech lighting system doing its nightly energy-saving dance. Five minutes before the lights are scheduled to go off, they flicker for 10 seconds, to alert late workers that they will soon be plunged into darkness. Each organization in the building sets its own lights-out time, so the flickering and blacking out extends through the evening. To avoid being caught in the dark, night owls can simply flick a manual switch or call the central office (which will turn on the overheads for two-hour stretches). The city’s Better Building Partnership helped implement this project as a means of preventing skyscrapers from squandering energy. In addition to the lights, First Canadian Place was updated with new boilers, air vents and water-saving technologies; the behemoth’s carbon dioxide output has been reduced by 27,000 tonnes a year—saving enough electricity to power a townlet of 4,000 homes.