Lighting control in miniature

A novel application of presence detection to control lighting in the Victoria & Albert Museum in London plays an important role in protecting 150 portrait miniatures on display in 17 cases. The gallery tells the story of the portrait miniature in Britain from its first appearance in the 1520s to its decline with the emergence of photography. They are painted in thin layers of watercolour on vellum or ivory and are therefore particularly sensitive to light. DHA Designs was required to control the total light exposure to limit fading and preserve these miniatures. It was decided to use Helvar infra-red sensors to provide lighting only when the miniatures are being viewed, using the company’s DIGIDIM system. As space is limited in the gallery, and the cases are close together, this was not easy to achieve. The sensors had to be customised to limit their peripheral sensitivity. When someone approaches a case, the light level is slowly increased from 10 lx to a maximum of 50 lx. After about 4 min, the lights are gradually dimmed again. The lighting system is designed to achieve about 20% exposure, amounting to 2 h in a 10 h opening day.