Luminaire Secto 4231 and the light distribution curve of it is shown below. The red curve shows the light distribution parallel to the wall and the blue one opposite to the wall.
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 was then rotated around the vertical axis for the illuminance recoding in other vertical planes.