The Last Supper, Leonardo da Vinci Lighting by iGuzzini, 2015
The specifications for the new lighting system defined by the Heritage Office focused on the need to limit lighting to the surface of the paintings, not illuminate the side walls of the refectory or the section of the vault above the paintings, restore the work's chromatic qualities, reduce the heat created by the luminaires and lower energy consumption. The design procedure consisted of two separate phases involving laboratory testing the luminaires and then defining the solution on site. The first phase was conducted in the ISCR light research laboratory with the aim of assessing the optimal spectral distributions. The new system features Palco spotlights fitted with Chip On Board LEDs installed on a DALI track including an iGuzzini control unit that can individually regulate the luminous flux of each spotlight. This creates a superior level of light uniformity on the painting while remaining within the lighting levels produced on the painting set by the conservation specifications defined and tested by the Higher Institute for Conservation and Restoration. The LED spectral quality and relative colour temperature were chosen following a visual assessment of the tests on the painted surface made by a commission of experts including the Head of the Milan Architectural and Landscapes Heritage Office, the Director of the Last Supper Site, the painting's Chief Restorer and the Director of the Lombardy Regional Museum Group, who together judged that the optimal colour balance produced by the spotlights is an LED colour temperature of 3384 K. On the basis of this decision a number of assessments were also made regarding conservation. Tests were made and all the measurements taken indicate that the consistent reduction of dissipated heat in the room achieved by the new lighting system has a positive effect on the stability of the exhibition environment.
from https://www.iguzzini.com/projects/project-gallery/a-new-led-lighting-system-for-leonardos-the-last-supper/