Abstract: A submerged planar illumination device for providing specified, substantially uniform distribution of light in liquid from one or few light sources such as LED. The device comprises a light guiding plate having an entrance edge to which the LEDs are fixed, a collimator for redirecting the light and forming substrate light which is coupled to a light guiding plate having at least one light extracting surface. Light extracting surface are optionally on both large surfaces of the light guiding plate. Each light extracting surface is covered with a pattern of light extracting and scattering elements capable of collecting, scattering and extracting light propagating in the light guiding plate into the liquid ambient medium in which the device is submerged. A cover, sealed to the entrance edge of the light guiding plate, protects the light emitting element from the liquid ambient medium.