An illuminated sign is not just a sign that lights. It is a fixed electrical installation on the outside of a building, and it brings a power supply, a fused spur, an accessible isolator, an IP rating appropriate to the exposure, and a maintenance obligation for the life of the sign.
Almost every illuminated sign also needs advertisement consent, which is the single most common reason a signage project runs late. Planning for both at the start is the difference between a six week programme and a fourteen week one.