The stained glass in Barcelona's historic Exchange Building, the headquarters of a Spanish telephone company, were commissioned to commemorate the 1992 Olympic Games. Located in Barcelona's Gothic Quarter, where Las Ramblas meets the city’s main public square, Edificio Telefónica was built between 1926 and 1928 and is considered Barcelona’s first skyscraper. Created in collaboration with the Centre del Vidre de Barcelona, Clarke produced four artworks for its lantern tower, each a pair of two windows, and the lunette above the main entrance.

Clarke’s lantern windows measure a total of 484 square feet of mouthblown and leaded stained glass. These windows were fabricated by students at the Centre del Vidre, where Clarke was Visiting Professor. The substantial stained glass artwork that was made for the three-light lunette above the building's main entrance on Plaça de Catalunya was removed in a 2013 refurbishment and is presumed lost.

On this commission, Clarke said:

‘The night-time expression of these works is as significant to me as the daytime one. The fact is that anything that glows, anything that actually has the appearance of containing and holding light is irresistible to me. Whether that is a glow-worm, whether it is a Belisha beacon – whether it is a lighthouse.’