The 58-year-old woman is being treated in hospital.
The accident happened in Barry Street, at its junction with Sunbridge Road, at about 12.40pm yesterday (August 3).
A silver Mercedes C180 mounted the pavement, colliding with the traffic light and knocking it over, causing serious injury to the woman who was standing nearby.
Police officers are keen to speak to anyone who witnessed the way the car was being driven before the collision or who saw the accident itself.
Information can be passed to the Western Area Safer Roads and Neighbourhood Support Team via 101, quoting log 870 of 03/08.