  The low-energy collective excitations of semiconductors and insulators often
couple strongly to light, allowing them to be probed optically. We argue here
that in fractional Chern insulators intra-band collective excitations are dark
in the sense that they couple anomalously weakly to light. This conclusion is
based on a relationship between ideal quantum geometry and the structure factor
of a Chern band, and on a classical plasma analogy motivated by the
vortexibility property of ideal Chern bands.
