Quote from an FA in the official report:
She attempted to contact FA3 at the rear of the aircraft, initially without success. She reported that it felt like a long time that she was trying to contactFA3. There was confusion while they attempted to communicate using a combination of the interphone, hand signals and the PA. The darkness in the cabin made the use of hand signals difficult and she could not see well enough to understand signals given by FA3.
Unquote.
Interesting point. With dimmed cabin lighting the length and width of the cabin affects the distance passengers and cabin crew can see. More obvious in a large aircraft than a A320/737 type. A dimmed cabin makes use of hand signals difficult. Maybe FA should be equipped with lighted wands like police manning booze buses and learn semaphore....