Turning off all electronic devices must be turned off or switched to airplane mode has become routine, flight attendants are reminded on every flight.
The pilot who has carried out many of these large flights confirms that leaving dim lights is a process to ensure your own safety and not just a dark / light issue.
Have you ever wondered why the crew on the plane requires you to lift the window up every time the plane takes off and landed?
The harsh environment on other planets in the solar system can destroy planes in scary ways.