  The I-table contains luminous intensity values over the range of angles for
the luminaires used in the road lighting in accordance with technical report
CIE 121:1996. A limited number of angles causes smoothing of the luminous
intensity diagram omitting possible local extremal values which affect the
calculations of the photometric parameters such as average illuminance, average
luminance, uniformity or treshold increment. The interpolating methods used to
calculate the luminous intensity can significantly improve the accuracy of the
calculations and redound to more effective and reliable road lighting design.
In the paper standard interpolation methods used up to now are compared with
newly proposed hybrid adaptive splines. Calculated values of luminous intensity
are compared and verified by goniophotometric measurements.
