Design of a Combined-Freeform-Surface Diffuse-Reflection System for High-Uniformity, Compact LED Inspection Illumination

LED diffuse-illumination systems are widely used in industrial inspection and real life because of their scattering properties. However, there has been little research on secondary optical designs for diffuse illumination. Considering the need for diffuse light in real life and work, combined with existing specular-reflection technology, this study proposes a design method for a combined-freeform-surface illumination system with specular and diffuse reflections. Considering that a separate diffusing device cannot effectively control the diffusion area of the light source, the unique properties of the specular-reflective device were utilized in this study. First, the specular-reflection device directs the light from the central portion of the LED to the diffuse-reflection device, and the light collected is then redistributed by the diffuse-reflection device. Two mathematical models were established according to the light-emitting angle of the LED, which corresponded to two freeform surfaces. In addition, when evaluating the uniformity of the target-plane illumination, a set of constraint equations was added to obtain the diffuse freeform surface contour of the target plane. Finally, the ratio of the diameter to the thickness of the resulting illumination system exceeded six, and the illumination uniformity increased to over 56% (with a uniformity improvement ratio of ≥6% compared to traditional single-freeform-surface systems and ≥10% compared to integrating sphere systems). It is specifically designed for industrial precision inspection scenarios, has higher illumination uniformity than other diffuse illumination systems, and has better compactness, making it suitable for high-precision inspection lighting applications.