  We evaluate radiation pressure from starlight on dust as a feedback mechanism
in star-forming galaxies by comparing the luminosity and flux of star-forming
systems to the dust Eddington limit. The linear LFIR--L'HCN correlation
provides evidence that galaxies may be regulated by radiation pressure
feedback. We show that star-forming galaxies approach but do not dramatically
exceed Eddington, but many systems are significantly below Eddington, perhaps
due to the "intermittency" of star formation. Better constraints on the
dust-to-gas ratio and the CO- and HCN-to-H2 conversion factors are needed to
make a definitive assessment of radiation pressure as a feedback mechanism.
