The treatment of an array of small metal particles as a continuous effective medium is shown to be possible for visible and near infrared frequencies at much larger particle sizes and separations than often supposed. Specific upper limits are evaluated for chromium. Results are based on the strongly correlated model. For this, the usual topology, variation, and attenuation of the field strength over average unit cell dimensions are permissible, provided such variations are characteristic of the effective medium as a whole. As wavelength decreases, the leading contribution to diffuse scattering off such composite films should come from terms proportional to &lgr;−8not the Rayleigh term.