Audience photographed in infrared light, 1930s.
© NMeM / Daily Herald Archive / Science & Society Picture Library
Photograph taken using the Ilford Infra-Red Process of an audience watching 'The Sign of the Cross' at the Carlton Theatre, London. The only light used was six infra-red lamps concealed on the balcony. Although the rays from these lamps were quite invisible to the eye, they emitted sufficient light to produce a fully exposed plate. This was the first time the special Ilford plates had been demonstrated outside the laboratory.