Evaluation of illumination uniformity metrics in design and optimization of light guides

Spatially uniform illumination is an important design target in many applications such as displays, backlights, medical lighting, solid-state lighting, microscopy etc. In the design process, optical systems are assessed using uniformity metrics based on the statistical analysis (min-max and min-average ratio, coefficient of variation) or using models incorporating features of human visual system (based on weighted contrast sensitivity function). In this contribution, we evaluate several uniformity metrics in the design of free-form and classical polygonal light guides. We implemented, in Zemax optical design software, various uniformity metrics as the constraints and as the terms in the suitable merit function. We compare influence of different uniformity metrics on the merit function landscape with respect to criterions such as number of local minima, robustness to parameter perturbation, sensitivity to numerical noise etc. In addition, we consider extension of standard approaches to color uniformity metrics. Our analysis and evaluation results can be used as a basis for choosing application specific uniformity metric.