Light: A perfect probe for gravity

In this talk the different possibilities offered by light (geometric effects, polarization effects, propagation delays and phase changes) for determining the local structure of space time, i.e., the gravitational field, in terms of the Riemann tensor, are discussed. Special attention is devoted to axially symmetric stationary gravitational fields. A description of the potentialities of ring lasers is presented, having direct reference to the GINGER project.