Through my long-term research on dozens of physical phenomena and experimental results related to light, I have summed up three related conclusions, which respectively explain the nature of light, the law of interaction between light and medium, the nature of light speed and the main factors that determine light speed. At the same time, it also shows that many physical phenomena and experimental results related to light can be explained only by using the most basic Coulomb law and Biot-Savart law in electromagnetism. This paper uses these three conclusions to explain the following 76 common physical phenomena and experimental results related to light at the same time, and has achieved unexpected success. Please correct your mistakes if you are interested. At the same time, I hope to collect more questions related to light through this paper to further test the applicability, reliability and correctness of these three conclusions. If these three conclusions can explain more physical phenomena and experimental results related to light without exception, it can be proved that the closer these three conclusions are to objective reality, the closer they are to truth. These three conclusions will be more accurate, objective and true in understanding and summarizing the nature of light, the law of interaction between light and medium, the nature of light speed and the main factors that determine light speed.