The difference in dB between the transmitted optical power and the optical sensitivity for a given probability of detection defines the optical link budget. This is an all-in-one optical specification of the LiDAR performance. To have a consistent LiDAR system, the optical link loss must not exceed the optical link budget. The analysis of the optical link loss mechanisms is essential to understand the environment conditions the LiDAR is operated on, and the validity of the predicted probability of detection. The optical link loss, when it is expressed in dB, is made by several additive components. The largest component is the unavoidable radiation loss mechanism, common to every radiative phenomena. The second loss term is the free-space attenuation of the medium. Other components of the link loss depend on the LiDAR front-end characteristics, others on the target characteristics. These concepts are extensively discussed in conjunction with the LiDAR maximum reach. The knowledge of LiDAR link budget and optical link loss allows the optimization of the probability of detection versus distance, under different link conditions.