  The light intensity distribution in a shower image and its implications to
the primary energy reconstructed by the fluorescence technique are studied.
Based on detailed CORSIKA energy deposit simulations, a universal analytical
formula is derived for the lateral distribution of light in the shower image
and a correction factor is obtained to account for the fraction of shower light
falling into outlying pixels in the detector. The expected light profiles and
the corresponding correction of the primary shower energy are illustrated for
several typical event geometries. This correction of the shower energy can
exceed 10%, depending on shower geometry.
