NOVELTY - The assembly has a mirror (1) and a facing panel (2) e.g. glass sheet, with a sealed gas space (5), where the mirror is selected from a group consisting of a mirror comprising a glass substrate (10), a silver coating layer (11) provided at a surface of the glass substrate and a paint layer (12) covering the silver coating layer or a mirror comprising an organic mirror film bonded to the glass substrate. The paint layer and the mirror film face the sealed gas space, where the sealed gas space is a low pressure space having a pressure less than atmospheric pressure.    USE - Mirror assembly for use in a solar energy reflector (claimed) of solar energy installation and heating installation in a solar power plant. Uses include but are not limited to a parabolic trough power plant, a central tower power plant e.g. heliostat power plant, a dish collector and a Fresnel reflector power plant.    ADVANTAGE - The assembly is luminous, and has high energetic reflectance after exposure to UV radiation. The substrate of the mirror and the panel are made of same material, so that expansion coefficients are same and internal stresses in the mirror assembly are minimized when the assembly is subjected to temperature changes. The mirror is arranged in a sealed state, thus reducing decrease of luminous reflectance and energetic reflectance of the mirror under exposure to UV radiation. The sealed state of the sealed gas space is maintained by the presence of sealing material in the assembly. The sealing material forms a barrier for ingression of moisture vapor and/or water in the assembly, and provides mechanical resistance to the assembly. The sealing material hermetically seals off the sealed gas space, and spaces the mirror and the panel from each other, thus avoiding the need of a frame or pillars.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a mirror assembly.    Mirror (1)    Facing panel (2)    Sealed gas space (5)    Glass substrate (10)    Silver coating layer (11)    Paint layer (12)