54|CUADERNOS of an installation where a luminaire, circular downlight type, is considered. The criteria for defining the luminous area of the luminarie has been modified; this allows us to do an analysis of the way the UGR values of the instalation change on the basis of the single data Led + optic and on the basis of the global ldts, using the luminous area and the equivalent luminous area. Calculation of the index of unified glare in interior installations To assess how the luminous area of a luminaire for interior lighting affects the result obtained from the UGR of the installation (unified glare rating), different lighting projects are done changing the area on the ldt file and performing the calculations as small independent luminaires formed of LED + optic. Luminaire used: luminaire composed of 12 Leds with incorporated optic. Exterior diameter of the luminaire (DE) = 325 mm Diameter of the area where the fountains are placed LED (DL) = 285 mm Diameter LED + óptica = 20 mm Configuration A: Starting from the photometric file from the luminaire’s trial. In this file a luminous area is assigned with a diameter (DL). Configuration B:Starting from the photometric file of the luminaire’s trial. In this file a luminous area is assigned whith a diameter that gives us a luminous area equal to the sum of the areas of the 12 Leds + optic that form the luminaire. Configuration C: Starting from the photometric file of the set Led+optic, conforming the luminaire on the project. The aim is to place each small defined luminaire (led+optic), in the position they have inside the actual luminaire. What follows are the results obtained using an environment simulation software to carry out different lighting projects and then analyzing the results of the unified glare rating. Every case has the same configuration and the calculations of the UGR are done at a height of 1.70 m. Shown bellow are the values obtained for the different cases: As the tables show, the illuminance values and the uniformity are practically the same in the 3 configurations (A,B and C), nontheless, when analizing the UGR value, it becomes apparent that in cases B and C, equal data is obtained, being case A very different from the former two. The data obtained is coherent with the actual definition of UGR, given that this value depends directly on the luminance of the luminous parts of each luminary in the direction of the observing eye. Remember that the luminance is inversely proportional to the area of emission of the source, which is why, if the area is expanded maintaining the intensity, the luminance is diminished. Lb is the background luminance Eind indirect vertical illuminance on the eye of the observer.