A light guiding system includes an ambient light gathering system for absorbing the ambient light to generate absorbed light; multiple light guiding devices each of which includes a light input end near the ambient light gathering system and a light output end near an incident side of a light guiding plate, and multiple light diffusion devices between the light output end and the incident side of the light guiding plate, for broadening a light-emitting angle of the light output end. The absorbed light enters the light input end and is guided to the light output end to form a backlight source. The light guiding system utilizes a light diffusion device to broaden the light-emitting angle of the light output end such that the light uniformity of the light output end is improved and the optical quality of the edge-lighting backlight module is raised.