A freeform collimator lens design for the Natural Light Illumination System

This paper presents the design of a collimator lens for use with the Lightbrick that uses total internal reflection as well as convex and concave surfaces. The Lightbrick is a light collector for the Natural Light Illumination System. The collimator lens is constructed using freeform surfaces which can be calculated through geometric-optics. Verified by optical simulation, using the collimator lens can achieve 90.3% luminous flux within ±2°, and optical efficiency improves by 48% in the collimator lens output. The collimator lens converges the light distribution of the Lightbrick and enhances the transmission efficiency of the Natural Light Illumination System.