Sometimes, air travel rules seem to challenge common sense. Why do we have to close our laptops but tablets can remain open? Why do we have to switch our phones to airplane mode and what happens if we don’t? Why do we have to wear seat belts while taxiing at 5 miles an hour, but not always while hurtling through the air at 500 mph?
Well, here’s another air travel rule that may seem arbitrary, but like many of the others, has sound logic behind it: If a flight takes off or lands when it’s dark outside, the interior cabin lights must be dimmed. You might think it would make better sense to keep them illuminated so that passengers can have better visibility inside the plane, but nope. Not so.
The reasons behind dimming cabin lights during takeoff and landing
First, when the lights are low inside the cabin, the illuminated emergency exit signs are easier to see. And second, during takeoff and landing (the phases of flight that are the most crucial when it comes to safety), it is key that passengers remain aware of their surroundings. A dim cabin helps with that: It allows everyone’s eyes to adjust so that they can see not only what’s in the plane but also what’s outside. If the cabin is too bright, crew and passengers wouldn’t be able to see out of the windows. (And if you want to know why window shades should be open during takeoff and landing, we have that answer too.)
“By pre-adjusting your eyes, you won’t be suddenly blinded while dashing for the doors in darkness or smoke,” says Patrick Smith, an airline pilot, travel blogger, and author of Ask the Pilot. “It also makes it easier for the flight attendants to assess any exterior hazards, like fire or debris. With the lights burning brightly, the glare would make it impossible to see outside.”
Ideally, the aircraft’s interior lighting should be matched to the exterior conditions, because it takes time for the human eye to adjust to its surroundings (like when you walk out of a dark movie theater).
The importance of being able to see out the window
Being able to see clearly outside can be extremely important on a flight. For example, in a British Airways incident in 2013, a plane’s engine covers popped open after takeoff, and because the problem was visible through the windows, the crew was able to make a quick emergency landing. In another instance, a United Airlines passenger on a flight from Newark to Venice saw through the window that fuel was leaking out of the wing.
Passengers need to be able to see clearly inside the plane too. According to the Flight Safety Foundation, in the event of smoke or fumes, passengers can lose as much as 83 percent of their wayfinding ability, and they may not be able to see exit signage right away. That’s why both the U.S. Federal Aviation Administration Code of Federal Regulations and the European Union Aviation Safety Agency require that an airplane’s exit-indicator path should be bright enough to be visible in darkness. In many cases, that floor-level lighting relies on glow-in-the-dark technology made from photoluminescent materials, ensuring that it will still work if the plane’s power is out. Dimming the cabin lights for takeoff and landing makes it easier to spot these in the event of an incident.