Optical design of a donut-shaped LED fill light to enlarge area for a smartphone flashlight

In this study, a wide-angle fill lamp was proposed through simulations and measurements to extend the illumination area of a smartphone's built-in flashlight. The lamp produces a donut-shaped light pattern that seamlessly integrates with the light distribution of an optimized smartphone flashlight. This enhanced flashlight provides a broader and more uniform light energy distribution, effectively addressing the issue of insufficient illumination coverage. Experimental results demonstrate that images captured using the enhanced flashlight exhibit better uniformity and a higher signal-to-noise ratio compared to those taken with the original flashlight alone.