The traditional lens has low focusing efficiency.

Theoretically, the convex lens can focus all the energy of the incident light on the light-receiving object, while the mirror will block the incident light to a certain extent, because the light-receiving object must be between the mirror surface and the light source. So the efficiency will be lower than that of concave lens.

In fact, the light transmission efficiency of convex lens and concave mirror (that is, the energy ratio of emergent light to incident light) cannot reach 100%. Convex lens will have reflection loss and transmission loss, and concave mirror will have reflection loss. Therefore, under actual working conditions, it is these losses and decisions that concentrate energy efficiently. Which side loses less, which side wins in the total centralized energy efficiency.