The Ardabil carpet forms the centre piece of the Jameel Gallery of Islamic Art at the V&A that opened in July 2006. Given the importance of the carpet to the collection, its prominence in the Gallery, and its size, the carpet will be displayed continuously for the duration of the gallery lifetime (over 25 years). To assure the carpet’s longevity and to be able to make valid decisions about the benefits ensuing from different lighting proposals, changes in the carpet on exposure must be determined and expressed in terms of visibility. The article describes the experiments on the carpet to determine, with a high degree of confidence, the response of different colours to illumination, together with the research resulting in a model of the likelihood of detecting a given colour change. Combining these two pieces of research, the solution of illuminating the carpet for 10 minutes in every half-hour whilst the gallery is open ensures an appropriate balance between the immediate visual impact and the long term preservation of the appearance of this uniquely beautiful carpet.