LIGHT DEFLECTION IN PERTURBED FRIEDMANN UNIVERSES

A new formula for fight deflection is derived using only physically observable concepts. The general result is specialized to cosmological perturbation theory and expressed in terms of gauge-invariant perturbation variables. The resulting scalar, vector, and tensor equations are supplemented by simple examples for illustration. The gravity-wave example may be of more than academic interest and even represent an alternative way to detect gravitational waves.