To plan an exhibition of cultural heritage in a museum it's necessary to consider different aspects, firstly the safe conservation of the exposed objects, secondly the optimal vision offered to visitors for their satisfactions and enjoyment. With regard to conservation aspects it's necessary to consider both the possible deterioration due to the radiation falling on the object and other aspects ... [Show full abstract] such as micro-climate conditions, frequency of visitors. Further important needs concern cheapness and low frequency of maintenance interventions by the curators. The study intends to examine existing light sources, in particular their lighting " quality " and to develop a new system, based on LED technology, able to combine visual valorization with protection of Cultural Heritage. In first phase the material to be investigated was realgar, a natural and artificial mineral, whose molecule consists of four covalent bonds As-S. In the presence of oxygen it undergoes a cyclic and autocatalytic photochemical transformation which causes an anisotropic volume increase of the crystalline unit cell and formation of AS 4 S 4 in the form, known as pararealgar. Analytical measurements have confirmed this hypothesis and allowed the definition of the reaction kinetics. In these experiments a 100 watt halogen lamp was used. Currently, the study is in progress, in order to understand the behavior of the pigment in the binder, the damages suffered and the eventual positive action of the degraded compound against biodegradation.