optically homogeneous
From Glossary of Meteorology
Homogeneous on the scale of the wavelength of the electromagnetic radiation of interest.
Pure liquid water is optically homogeneous over the visible spectrum because one cubic wavelength of water contains many molecules, whereas a cloud of water droplets is not optically homogeneous. Optical homogeneity is more general than transparency, usually restricted to visible wavelengths. A body is said to be transparent if it transmits images. Optical homogeneity is necessary for transparency but not sufficient. A sufficiently thick sample of an absorbing optically homogeneous material would be described as opaque rather than transparent.
