When you board an airplane and find your seat, you might notice that the cabin lights dim during takeoff and landing. This common practice has nothing to do with helping you get some rest.

Instead, it’s a crucial safety measure designed to prepare passengers and crew for potential emergencies. Here’s why dimming the cabin lights is more than just a routine procedure.

Safety Precaution: Adjusting to Darkness

The primary reason for dimming the cabin lights during takeoff and landing is to help passengers’ and crew members’ eyes adjust to the lower light levels. “During dawn, dusk, and night, flight crews dim the lights so that in case of an emergency where passengers and the flight crew have to abandon the aircraft, their eyes already are adjusted to the dark,” explains Dan Bubb, a former airline pilot and current associate professor at the University of Nevada, Las Vegas. It takes about 5 to 10 minutes for eyes to adjust from bright light to darkness, and this adjustment is critical if an evacuation is necessary.

Critical Phases of Flight

Takeoff and landing are the most dangerous times in an aircraft’s journey. According to Boeing, 21% of fatal accidents occur during takeoff and initial climb, and 46% happen during final descent and landing. During these phases, pilots are extremely busy monitoring aircraft systems, scanning the environment, and following air traffic control instructions. The aircraft is also in a “dirty configuration” with wing flaps and landing gear down, making it more vulnerable to issues.