34|REPORTAJE In the less successful attempts, light is only used to highlight the surface of an object. In this way it becomes a secondary tool with little impact on the final result. However, the most interesting situations take place when light is used as an architectonic object in itself and rises to the same level of the volumetric composition that we architects use to delimit a space. And what are the parameters that relate the constructed (or substracted) mass and light? Tension. Tension will be the most consciously repeated concept in this article. Tension understood as a set of internal and unstable forces that any project has to contain and which reach the height of their expression when in harmony. This could be compared to more tangible situations, for example, a magnet and its magnetic field. We all know that the magnet has a different polarity in both ends: positive and negative. Depending on the distance in which we place another magnet with inverted poles, a series of magnetic forces will start working to attract them. If they are to far, the magnetic field does not activate;but if they are very close they will invariably join together. The moment I want to piont out is when they are at a distance where they do not separate or join together. At this moment they begin to vibrate, they come in tension and they hold the system in a sort of suspended collapse This instant is very suggestive; where the forces of attraction and repulsion are in equilibrium and vibration is the physical fact that materializes the balance of tensions. Density and massiveness, porosity, geometry... will also be physical properties of light that will help us understand its use as a tool for projects, considered at the same level of architectonic form. Within its characteristics we should find the same tension and unstable equilibrium as the one found in the magnetic field. Abstraction in the configuration of interior spaces through the use of geometrical forms and light did not originate in the XXI century. We find examples as far back as the Agripa Pantheon in the II century A.D., where the natural light caresses the interior parameters of the hemispherical dome over a circular drum and the pavement giving the space a tension, a sublime vibration. Lighting of the Castle of Buitrago of Lozoya Buitrago of Lozoya is located at a few 80 kilometers north of Madrid. Surrounded by the Lozoya river, the city was founded in the XI century and still preserves its walls intact. It is one of the most important walled areas of the Madrid Community. The castle is located at the end of the wall in order to stregthen one of the corners for protection. Today, its Weapons Courtyard is used for cultural shows and holds more than one thousand five hundred people. With a budget of only eighty thousand euros, the program needed to outfitt the architectonic complex with artistic and versatile lighting with enough flexibitity to accommodate from a jazz concert to the live nativity scene that is done every year during Christmas. On the map of the town we can see three architectonic elements that stand out for their geometry: the Church located in one of the corners; the castle at the opposite end and to the north, three cylindrical bases were the heavy armament, used to defend the city, was located. Inside the