Which of the following is a requirement for the visibility of egress routes?

Illumination is a fundamental requirement for the visibility of egress routes in buildings. Proper lighting is essential to ensure that occupants can easily identify exit paths and navigate safely, especially in emergencies. Inadequate lighting can lead to confusion and hinder evacuation efforts during power outages or emergencies, thereby increasing the risk of injuries.

The other choices do not directly relate to visibility in the context of egress routes. Textured flooring, for instance, may provide traction but does not enhance visibility. Natural ventilation and wider doorframes might contribute to comfort and accessibility in a building's design but are not primarily aimed at ensuring that egress routes are clearly visible in emergency situations. Thus, illumination stands out as the key requirement for the visibility of egress routes.