The Light Environment Changes with Depth
Discover how the light environment changes dramatically with ocean depth in Grade 8 science. Students learn that selective water absorption removes red wavelengths first, so below 100 meters only blue and green light exists—red light physically does not reach the deep ocean.
Key Concepts
Because of this selective absorption , the spectrum of available light changes as you go deeper.
By the time you reach 100 meters deep, all red light has been absorbed by the water above. The "light environment" at this depth consists only of blue and green wavelengths.
Common Questions
Why does light change color as you go deeper in the ocean?
Water selectively absorbs different wavelengths at different depths. Red light is absorbed first and disappears by about 100 meters deep. At greater depths, only blue and green wavelengths remain—red simply does not exist there.
What does the light environment look like at 100 meters underwater?
At 100 meters depth, all red light has been absorbed by the water above. The only available wavelengths are blue and green. This drastically affects how colors appear—a red fish looks black because there is no red light to reflect.
How does the changing light environment affect deep sea organisms?
Deep sea organisms have evolved visual systems and pigments adapted to blue and green wavelengths. Since red light is absent, many deep-sea animals have evolved to be red (which appears invisible in blue-only light) as a form of camouflage.