Cylindrical illuminance and modelling are two indexes important for visual comfort.

The cylindrical illuminance is aimed at guaranteeing an optimum luminance of all solid objects, people’s faces in particular.

Therefore an adequate mean cylindrical illuminance value must be guaranteed in all areas where people move.

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.

In all rooms where an optimum visual communication is required (e.g. offices, classrooms, meeting rooms), the mean cylindrical illuminance must not be lower than 150lx. Illuminance uniformity must not be lower than 0.1 in both cases.

Modelling instead is the balance between diffuse and directional light. The modelling index is the ratio of cylindrical to horizontal illuminance on the same measuring point of the grid. 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 negative effects of a poor modelling value can be counterbalanced by daylight. Therefore modelling values not included in the above range may also be accepted.

Cylindrical illuminance is the mean value of vertical illuminance rotating around a certain measuring point.