Fig. 1. Double free-form surface lens model and illuminance distributions simulated under different light sources. (a) Double free-form surface lens model; simulated illuminance distributions for (b) point light source, (c) extended light source, and (d) extended light source array

Fig. 2. Schematic diagram of lens design

Fig. 3. Simulated illumination distributions of traditional TIR lens. (a) Point light source; (b) extended light source

Fig. 4. Design schematic diagram of surface S₁

Fig. 5. Microstructure design diagram

Fig. 6. Illuminance curve of surface S₁ for extended light source

Fig. 7. Schematic diagram of optimization design of surface S₁-1

Fig. 8. Illuminance curves of surface S₁ and optimized surface S₁-1 for extended light source

Fig. 9. Illuminance curves of surface S₁-1 and quadratic optimized surface S₁-2 for extended light source

Fig. 10. Extended light ray graphs. (a) Surface S₁-1; (b) quadratic optimized surface S₁-2

Fig. 11. Simulated illuminance diagrams of lens. (a) Extended light source; (b) extended light source array

Fig. 12. Illuminance curves based on extended light sources with traditional double free-form surface lens and lens designed in this paper