Fig. 1. Structure of indoor natural light illumination system

Fig. 2. Clipping process of light collection module. (a) Double paraboloid structure; (b) structure is obtained by removing outer edge of double paraboloid structure and spherical part from lower surface; (c) height change of light collection module

Fig. 3. Other optical elements in the system. (a) Visible light are transmitted and invisible light are reflected to photovoltaic cell by PBS; (b) five LEDs are bonded with lightguide plate entrance; (c) fiber beam are coupled into lightguide plate exit; (d) light emitted from LED converge through CPC

Fig. 4. Overall structure of natural light illumination system

Fig. 5. Changes of luminous flux. (a) Effect of different times and lightguide plate thickness on indoor luminous flux; (b) luminous flux provided by sunlight and LED light source and received total luminous flux

Fig. 6. Effect of different parameters on optical concentration ratio. (a) Light collection module width; (b) parabolic coefficient

Fig. 7. Effect of light collection module width and parabolic coefficient on optical concentration ratio

Fig. 8. Effect of height of light collection module on optical concentration ratio and CAP value when coupling structure radius are different. (a) 0.1 mm; (b) 0.2 mm; (c) 0.5 mm

Fig. 9.

Test system of concentrator

Fig. 10. Effect of number of light collection modules on geometrical concentration ratio and optical efficiency

Fig. 11. Fiber output illuminance and solar irradiance versus time in different weather conditions. (a) Calm weather; (b) cloudy weather