An optical lens has a beam angle within 29-46 degrees, and includes: an output light region including a first output light surface, a second output light surface around the first output light surface, a buffer surface connecting the first and second output light surfaces, and an outer surface around the second output light surface; an incident light region including a planer incident light surface and an inner surface, the planer incident light surface opposing the first and second output light surfaces, the inner surface around the planer incident light surface and opposing the outer surface, the planer incident light surface and the inner surface connected to each other and forming a slot denting toward the first output light surface; and a mounting portion around and extending outside with respect to the output light region and the incident light region.