When the One Canada Square was built in 1991, it was the tallest building in the United Kingdom, standing at 234.8 metres (770 feet) above ground level. Those who work, live, or simply visit London will be all too familiar with perhaps the most distinctive feature of Canada Water Square – the white flashing light at the top of the tower.
In this article, we explain what the lighting is for and why it is the only flashing white light in the sea of red lights across the Canary Wharf skyline.
Figure 1: Canary Wharf at night. 
Tall structures in the UK, such as buildings and wind turbines, require lighting at night so that they can be identified by aviation pilots. The relevant guidance in the UK pertaining to the lighting of obstacles was produced by the Civil Aviation Authority (CAA) Civil Aviation Publication (CAP) 168: Licensing of Aerodromes  document.
The relevant excerpt for typical lighting requirements is as follows:
4.101 Obstacle lights should be used to indicate the existence of objects which are to be lit as follows:
- Low intensity steady red obstacle lights should be used on obstacles less than 45 m high, except that medium intensity steady red lights should be used to light such obstacles as an elongated structure, an obstacle in the outer area of the approach or high ground adjacent to the aerodrome circuit. There are two types of low intensity obstacle lights for fixed obstacles:
Group A and Group B (see table 6A.1).
- a) Low intensity Group A lights should be used for obstacles on the movement area where Group B lights may cause dazzle.
- b) Low intensity Group B lights should be used away from the movement area or in areas on the movement area with high levels of background illuminance.
- Medium intensity red steady obstacle lights should be used on obstacles between 45 m and less than 150 m in height.
- Medium intensity steady red obstacle lights should be used to indicate the presence of:
- a) an obstacle if its height is 150 m or more; or
- b) a tower supporting overhead wires, cables etc. of any height where an aeronautical study indicates such lights to be essential for recognition of the presence of the obstacle.
It is stated that steady red lighting is required for fixed obstacles, with two types of intensities. This is clear when you consider all of the other buildings within Canary Wharf (and central London), which all have steady red lighting.
Why the White Light?
You may have noticed that there was no mention of white flashing lights within the CAP 168 excerpt. So why does the One Canada Square building have a white flashing light? Well, the document goes onto say:
4.102 However, where an aeronautical study conducted by the CAA concludes that greater conspicuity of the obstacle through the use of a higher specification light is required, the use of a high intensity flashing white obstacle light will be considered by the CAA.
4.103 The combination of white and red obstacle lights should not be used at the same time to light an obstacle.
This section confirms that high intensity flashing white obstacle lighting should be implemented if an aeronautical study concludes it is required. In the case of One Canada Water, the building is in proximity to London City Airport and under the extended runway centreline.
An aeronautical study was undertaken during the planning process for the building, and it was determined that the increased obstruction risk of the building for approaching and departing warranted the flashing white light.
Pager Power can determine the aviation lighting requirements of tall structures and design appropriate lighting schemes to ensure compliance with the aviation guidance and acceptability by stakeholders such as airports.
If you are working on a tall building, wind development, or any other structure and require assistance on aviation lighting, please do not hesitate to contact me at email@example.com.
 – Civil Aviation Authority (2022) CAP 168: Licensing of Aerodromes. Available at: https://publicapps.caa.co.uk/docs/33/CAP%20168%20Licensing%20of%20Aerodromes%20v12%20c1022.pdf (Accessed: February 15, 2023).
 Pixabay (June 2007) on Pexels.com. Last accessed on 21st February 2023. Available at: https://www.pexels.com/photo/white-concrete-building-with-lights-88514/