  The ability to manipulate the refractive index is a fundamental principle
underlying numerous photonic devices. Various techniques exist to modify the
refractive index across diverse materials, making performance comparison far
from straightforward. In evaluating these methods, power consumption emerges as
a key performance characteristic, alongside bandwidth and footprint. Here I
undertake a comprehensive comparison of the energy and power requirements for
the most well-known index change schemes. The findings reveal that while the
energy per volume for index change remains within the same order of magnitude
across different techniques and materials, the power consumption required to
achieve switching, 100% modulation, or 100% frequency conversion can differ
significantly, spanning many orders of magnitude. As it turns out, the material
used has less influence on power reduction than the specific resonant or
traveling wave scheme employed to enhance the interaction time between light
and matter. Though this work is not intended to serve as a design guide, it
does establish the limitations and trade-offs involved in index modulation,
thus providing valuable insights for photonics practitioners.
