A contour calculation method for rapid freeform reflector construction with ellipsoid patches

•We introduced a contour calculation method for LED-based freeform reflector.•We use 6400 ellipsoid patches to establish a freeform reflector.•The freeform reflector illuminates a square illumination distribution.•The designed freeform reflector offers high uniformity and tolerance.•The computation time of the freeform reflector is just 18.5 s.

This paper presents a contour calculation method (CCM) for the freeform reflector design. Conservation of energy relates the light flux from a Lambertian-type point source to a desired irradiance and a discrete spot distribution on a target plane. This relationship determines the edges of the reflector patches, thus, enabling the design of a non-imaging freeform reflector based on a series of ellipsoid patches modeled as NURBS curves in Rhinoceros. As an example, we present a freeform reflector design composed of 6400 ellipsoid patches to illuminate a surface with 94% uniformity. A computer calculation takes 18.5 s.