Several investigators have conducted experiments on the angular distribution of light in natural waters (1, 2). It has been found that the direction of maximum light intensity from the sun moves toward the vertical with increase in depth. It has also been found that light becomes more diffuse but remains highly directional with increase in depth....
Whitney, Lester V.. 1941. "The angular distribution of characteristic diffuse light in natural waters." Journal of Marine Research 4, (2). https://elischolar.library.yale.edu/journal_of_marine_research/589