I will discuss the rational of a family of theorems about the existence of light rings based on the concept of a topological charge of light rings. One particular theorem establishes that stationary and axisymmetric ultracompact objects that can form from smooth, quasi-Minkowski, physical initial data must have at least one stable LR. Such LR has been argued to trigger a spacetime instability. Using ultracompact bosonic stars as a testing ground for the instability, we will confirm the LRs triggered instability, identifying two possible fates: migration to non-ultracompact configurations or collapse to BHs. These results support that the LR instability is effective in destroying horizonless ultracompact objects that could be plausible BH imitators.