If you thought pilots dimmed（调暗）the lights before takeoff to give you some shuteye, think again. Believe it or not, the dim lighting could actually help save your life in case of a plane emergency.

    The dimmed lights before taking off the runway and landing are a flight precaution used to help passengers' eyes adjust quicker during an emergency escape. “Going from a brightly lit environment to one that's completely dark would require some time for our eyes to focus and see the escape slide,” Alice Theriault, service director for Air Canada wrote in a press statement. “Since we need to have all the seconds on our side in the event of an emergency, dimming the lights is one of many steps we take to ensure the safety of our customers.”

    The phenomenon that your eyes see those strange speckles (小斑点) as your sight adjusts to a dark place after being in a light place is called dark adaptation. It normally takes our eyes about 20 to 30 minutes to see best in a dark room. The brighter the lights, the longer it takes for our eyes to adjust, which is why dimming the plane lights could shorten your “dark adaptation” time since you haven't been sitting under fluorescent bulbs (荧光灯) all flight.

    Not only does dimming lights add valuable time to the escape process, it reduces the tension on your eyes if you need to look outside, or see the emergency lighting along the passage. “Ithelps keep you in the right direction.” Patrick Smith, an airline pilot and author of Cockpit Confidential told The Telegraph. “It also makes it easier for flight attendants to assess any outside risks, such as fire or debris, that might affect an escape.” So next time a pilot dims the lights, just know it's for your safety, even though it creates a gentle atmosphere for your takeoff into the sky.