Luminaire Victo 4250 and the light distribution curve of it is shown below. Since the luminaire is symmetric the light distribution curve is similar at every C-plane.
This measurement is performed for giving accurate light intensity distribution data for llumination modeling. This information can be used e.g. with DiaLux modelling software to model how the lighting changes the ambiance in a room.
The light intensity distribution of the luminaire is measured by moving a detector of a photometer around the luminaire recording illuminance in one vertical plane (C-plane). The luminaire can be rotated around the vertical axis for the illuminance recoding in other vertical planes. Here, however, the luminaire is rotationally symmetric and light distribution in every vertical plane is the same.