St Martin's, through a glass lightly

Prince Charles and the Archbishop of Canterbury will lead a service of thanksgiving to mark the £36 million transformation of St Martin-in-the-Fields.

The service on Monday comes as the Trafalgar Square church unveils the final addition to its refurbished interior.

The East window in etched glass is by former Turner Prize nominee Shirazeh Houshiary, an artist born in Iran in 1955 who has lived in London for three decades.

It replaces a window with a blue cross installed after wartime damage but deemed inappropriate with the church restored to its 18th century glory. The Georgians had plain glass in their windows.

Houshiary, who collaborated with architect Pip Horne, said: "I don't really believe in any religion but I'm interested in architecture and I visit churches and temples. I love them. Our thinking was the church is a very beautiful piece of architecture. The light pours in and you understand how magnificent it is."

The result is an abstract "warp and weft" design intended to evoke the Cross. Nicholas Holtam, vicar of St Martin's, said it was a fantastic design, adding: "It is also, hopefully, significant to have an Iranian woman making a significant work for a Christian church in London."

The church still has £2.5 million to raise to pay for restoration of a terrace of John Nash properties for its work with the homeless.