Illuminance of Ocean Depths

the amount of luminous energy that reaches the ocean depths. The illuminance of ocean depths depends on (1) the illuminance of the ocean surface, which, in turn, is determined by the height of the sun above the horizon and by the transmittance of the atmosphere, (2) the nature of the ocean surface (ice cover, waves), and (3) the optical properties of seawater. When solar radiation enters water, it is attenuated by absorption and by scattering. Both of these processes depend on the wavelength λ of the light. The red rays of the solar spectrum are absorbed the most and the violet rays are scattered the most. As a result, the blue-green rays with λ of 0.48–0.50 micron (μ) penetrate the greatest distance into pure seawater. As the depth increases, the wavelength having maximum penetration is shifted toward λ = 0.45-O.46 μ and blue light becomes predominant. The maximum illuminance of the ocean surface, with the sun at the zenith and for a pure atmosphere, can reach 140,000 lux. In this case, in the clear waters of the open ocean, at depths of about 50–60 m, the illuminance can attain a value of 20 lux, which is sufficient for reading.