During your travels, you may have seen cabin lights dimmed before an airplane lands at night. Although you might not have known it, there is a good reason why this is done. An airplane's cabin lights are dimmed before landing at night so that passengers’ eyes can adjust in case of an emergency evacuation.
It is common knowledge that when one suddenly moves from a brightly lit room into the dark, initially it is very difficult to see. This is because it takes time for our eyes to adjust to changes in light levels. Even though it takes several hours to acquire optimum vision in darkness, there are significant changes to vision sensitivity within the first few minutes in a darkened environment. By dimming the cabin lights before landing, airplane crews make it possible for passengers' vision to adapt to the dark much more quickly. This way, if there is an emergency situation, passengers will be able to see where they are going and evacuate the plane safely.
More airplane emergency tips: