Submerged planar illumination device

A submerged planar illumination device comprising:

• a light guiding plate having:
• at least one light extracting surface;
• at least one collimator;
• and
• an entrance edge;
• at least one light emitting element generating light, wherein each of said at least one light emitting element is disposed so as to couple input light from said light emitting element into said entrance edge, wherein said input light forming a corresponding substrate light component which propagates through said collimator by reflection, wherein said substrate light component exits from said collimator and propagates through said light guiding plate by total internal reflection;
• and
• a cover, sealed to said entrance edge of the light guiding plate, protecting said at least one light emitting element from liquid ambient medium,
• wherein said submerged planar illumination device is capable of being submerged in liquid ambient medium such that said at least one light extracting surface is being submerged into said liquid ambient medium, said light extracting surface is having a pattern of light extracting and scattering elements capable of collecting, scattering and extracting light from said substrate light component forming extracted light propagating into said liquid ambient medium, wherein the pattern of light extracting and scattering elements distributed on said at least one light extracting surface in a non-uniform pattern configuration that is substantially a two-dimensional, non-monotonic irregular function.