![]() Generally speaking, light sources with an Ra equal or higher than 80 are assigned good chromatic yield properties. As the performance worsens a lower mark is granted. ![]() If none of the samples change chromatically, the light source is recognised an Ra of 100. Secondly, eight sample colours are lit by the lamp being studied, and the results are compared with those of a “black body” which has been taken to the same colour temperature. ![]() The chromatic yield indicator (Ra) is a system that has been derived from vision experiments to assess the impact exercised by different light sources on the colour that is perceived of items and surfaces.įirst of all the colour temperature of the light source must be identified. This need varies with the item: generally it is more marked for multi-coloured items and lower in monochrome items. The chromatic yield of light source corresponds to the ability to recognise the colours of an exposed item. This measurement is expressed in Kelvin degrees (K). As the temperature increases, the black body gradually changes from red to orange, to yellow, to white to finally reach white-sky blue. The theoretic principle this measurement is based on is the “radiating black body”. The colour temperature of a light source is based on the principle that an incandescent item changes colour as the temperature increases. For both uniformity must be equal to U0 ≥ 0.10. The standard moreover specifies that a lower illuminance level may be accepted should the above-mentioned level not be complied with due to the dimensions and the complexity of the rooms or to operational factors.įor example, poor mean illuminance values are accepted in case of high ceilings with suspended lighting fixtures located far from the ceiling.įor rooms where visual activities or tasks require luminous surfaces, such as offices, schools and hospitals, the mean illuminance values should be 75lux for walls and > 50 lux for ceilings. The reasons for the introduction of this provision are based upon the fact that both walls and ceiling are included in the observer’s field of view (also called background) and are therefore of the utmost importance for the environment visual comfort. The 12464-1:2002 standard did not contain any provisions concerning these surfaces whilst the 12464-1:2011 standard establishes that mean illuminance should be: Therefore modelling values not included in the above range may also be accepted.Ĭylindrical illuminance is the mean value of vertical illuminance rotating around a certain measuring point. The negative effects of a poor modelling value can be counterbalanced by daylight. An adequate modelling value ranges between 0.3 and 0.6 in case of a uniform distribution of the lighting fixtures or of a luminous ceiling. The modelling index is the ratio of cylindrical to horizontal illuminance on the same measuring point of the grid. Modelling instead is the balance between diffuse and directional light. Illuminance uniformity must not be lower than 0.1 in both cases. ![]() offices, classrooms, meeting rooms), the mean cylindrical illuminance must not be lower than 150lx. In all rooms where an optimum visual communication is required (e.g. The mean cylindrical illuminance values must not be lower than 50lx on a plane at a height of 1.2m for seated persons and of 1.6m for standing persons above floor level. Therefore an adequate mean cylindrical illuminance value must be guaranteed in all areas where people move. The cylindrical illuminance is aimed at guaranteeing an optimum luminance of all solid objects, people’s faces in particular. Cylindrical illuminance and modelling are two indexes important for visual comfort. ![]()
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