Secondary light distribution design of COB extended light source based on double free-form surface

The direct design method is employed to fashion the double free-form surface of the COB light source, addressing issues of limited energy utilization and uneven illuminance or intensity in the light source's illumination area. This approach integrates the principles of edge lighting, Snell's law, and Fermat's principle to directly undertake the secondary light distribution design for the COB light source, without relying on optimization algorithms. This ensures swift calculations and attains a high energy utilization rate along with excellent illuminance and intensity uniformity. Using a COB surface light source with a diameter of 25 mm as an illustrative case, a free-form surface lens with a central height of 38 mm was crafted to yield rectangular light spots exhibiting uniform illuminance and intensity distribution on the receiving surface. The resulting root mean square error for intensity stands at approximately 0.38, while the energy utilization rate reaches 91.68%. Similarly, the root mean square error for illuminance is around 0.25, with an energy utilization rate of 90.26%.