Light bends when it hits water so it can only travel so far. So the deeper you go the less light there will be.
Explanation:
The ocean is broken into three zones based on intensity and light level. The upper 200 meters (656 feet) of the ocean is called the euphotic, or "sunlight," zone. This zone includes the vast preponderance of commercial fisheries and is home to many preserved marine mammals and sea turtles.Only a small amount of light penetrates behind this depth.The zone between 200 meters (656 feet) and 1,000 meters (3,280 feet) is usually regarded to as the “Twilight” zone, but is authorized the dysphotic zone. In this zone, the intensity of light rapidly consumes as depth increases. Such a miniscule amount of light penetrates beyond a depth of 200 meters that photosynthesis is no eternal possible.The aphotic, or “midnight,” zone survives in depths below 1,000 meters (3,280 feet). Sunlight does not perceive to these depths and the zone is immersed in darkness.