designer's own words:The door is a passage for people to come in and out. Opaque hinged doors are widely used in offices, classrooms and other public facilities. However, people might bump against each other in a crowded place when they use the door at the same time on the opposite direction. Such accidents frighten or even injure people. LED light sign of the door can prevent people from bumping against each other when they come in and out through an opaque hinged door.