We present a manifestly conformally invariant formulation of Maxwell e
quations on asymptotically flat space-times. It is shown how to constr
uct regular self-dual and antiself-dual fields from suitable radiation
data, and the general solution as a sum of fields with both types of
duality. The basic variable in this formalism is a scalar field F defi
ned as the phase of the parallel propagator (associated with the Maxwe
ll potential) from interior points to future null infinity along null
geodesics. Field equations equivalent to the source free Maxwell's equ
ations are derived for F. A perturbative solution based on Huygens' pr
inciple is proposed. Exact solutions are found for H-spaces. The use o
f these results on gravitational lensing is discussed. (C) 1996 Americ
an Institute of Physics.