Abstract: A light pipe for use in aqueous environments comprising an optical rod capable of total internal reflection, and disposed in the optical path of a light source such as a light emitting diode or other source. The optical rod has frosted and unfrosted portions, such that the light is propagated distally along the rod at the unfrosted portions, but a portion of the light is coupled out of the rod into the aqueous environment at each of the frosted portions. The relative sizes of the frosted portions are arranged so that substantially the same light power is coupled out of the rod at each frosted section, thus facilitating rapid and uniform growth of algae in the aqueous environment.