A note of spectral fidelity analysis of natural light passing through optical fiber and air at different distances

•Relationship between color rendering index (CRI) and transmission distance.•Comparison of output spectrum of natural light transmitted by different media.•Attenuation curve analysis of PMMA optical fiber, silica optical fiber, and air. Direct use of sunlight for building lighting is a new way of using the sun. In this study, the distortion of the output spectrum of natural light after passing through PMMA plastic optical fiber, silica optical fiber and heliostat is analyzed, and the suitable transmission distance of different light transmission media is explored, which provides guidance for the design of subsequent optical fiber lighting system. This study concluded that: (1) Over 5 m PMMA plastic optical fiber transmission of natural light will appear very serious distortion phenomenon, will make the CRI value (Ra) less than 90; (2) Silica optical fiber has a slight distortion of the spectrum, and CRI value can be maintained to 95.7 at 100 m; (3) The distortion of the spectrum by air is weaker. It is almost negligible in the range of 100 m.