LIGHT DEFLECTION IN PERTURBED FRIEDMANN UNIVERSES

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