Reverse functional design of discontinuous refractive optics using an extended light source for flat illuminance distributions and high color uniformity

We propose a reverse functional design of modified Fresnel lens (MFL) with discontinuous refractive surfaces to achieve cost-effective high optical performance with thin lenses. The reverse-geometry design process was optimized to control the spatial illuminance distribution (SID) of light-emitting diodes (LEDs). Analysis results based on non-sequential ray-tracing simulations for flat SIDs indicated that the illuminance uniformity of LEDs with optimum MFL with different groove angles increased about 22 times, from 0.348 to 0.016, compared with the normalized standard deviation (NSD) of the general Fresnel lenses (GFL) with groove angles of 0 degrees. In addition, the proposed method enhanced the color uniformity by reducing the circular yellow pattern. Tolerance analysis was carried out to determine tolerance limits for applying the optimum MFL in the assembly process. Finally, the feasibility of the reverse design process was verified by optical measurements of the optimum MFL. (C) 2011 Optical Society of America