Relighting the interior of St Paul’s is probably one of the greatest challenges ever undertaken by Speirs + Major. The architectural and iconic value of the building, its long and remarkable history and the complex mix of worship, tourism and spectacle combined to make it a monumental task.

The multi-award-winning solution lay in seeing the scheme as a series of layers that fell into distinct categories: general, architectural, liturgical and theatrical lighting. The idea was that each layer can either stand independently or be combined to provide variety and flexibility.

The general lighting is provided by a series of new and refurbished chandeliers, converted gasoliers and stall lights, together with specially designed lighting bars that can be folded away to restore the look of the space.

The architectural lighting comes from concealed metal halide, linear xenon, cold cathode and tungsten halogen sources. It includes the uplighting of the main vaults, the dome, transept windows, organ and other major features.

The liturgical scenes are created by local lighting to the various altar positions. Supplementary theatre lighting serves the crossing. In addition to these main layers, lighting to entrances was improved and the theatrical lighting systems used for events were upgraded.

There were numerous constraints, including gaining permission from many official bodies. Planning involved extensive research into minimising damage to the fabric, as well as mock-ups and tests. Other issues included disabled access, the illumination of artworks, limited availability of power and the need to develop a sustainable solution. Achieving the right balance between the operational and aesthetic requirements was key. Carrying out the scheme in a fully operational building was also a considerable challenge as work was only permitted at night. The project took four years to complete.

The final outcome is seen by all parties as a great success and has been described within the conservation and heritage world as a benchmark project.