18|AULA cd uniformity degree (<0,2) and is normally associated to the reinforcement or stress of the elements or areas that intend to be outstanding for their lighting emphasis. » Mixed Systems The present diversity of usages and spaces makes the use of systems combining uniform with localized lighting very frequent. The current state of regulation and control technologies allow us to have an enormous diversity of illuminated scenes, even for a unique system, which allow us to respond to changeable necessities with great versatility. The main lighting characteristics of the mixed systems share the advantages and disadvantages of the uniform and the localized systems. 2.3 Classification of the systems according to the Visual Perception in space. Lightning systems have an important visual presence in the architectonical space; thus it is convenient to analyze them according to their physical presence and to the visibility of their emitter surfaces. These are characterized by their formal, dimensional, chromatic and aesthetic appearance. Considering the capacity of being seen by the beholder, systems can be classified in: Visible and Non Visible. In this classification we will only refer to the luminaries, although a partial perception of the different elements composing the lighting system is also observed, like the support structures, the wiring, the peripheral equipment, etc. » In non visible lighting systems, light effects predominate in space, in the different surfaces and in the architectonical elements. These operate as spotlights that acquire a particular “luminary” role. The color, the texture and the form of the chosen space, defined by its architecture, are main features of the elements that appear bathed by the luminous flux coming from the hidden lighting system. » Systems can be Non Visible because they are hidden in elements of the building itself, such as: cantilevers, cornices, cavities, corners, etc; or rather added, because they are located in places that were originally intended for that purpose in the building design, or to make part of the elements that form the architectonical space, like walls, roofs, furniture elements, facings, etc. The classification of the systems proposed by Norbert Lechner is included in the classification of non visible systems that we suggest. We are dealing with two different ways of hiding lighting systems, which give rise to what we call Hidden and Integrated lighting systems. » Hidden Lighting Systems use a space that was not initially conceived to this aim in order to place the luminaries. In most of the cases, hiding a lighting system implies an indirect illumination of the work plane or the hanging, this makes the illumination become a general Sistema mixto. Museo de Historia Natural, Tenerife.