Did you know that blood turns green at the bottom of the sea? For this effect to occur, you don't have to go very deep (considering that the depths of the ocean are greater than we can imagine): about 20 meters from the surface, the effect already happens and it's not an optical illusion - the blood itself is green.
But why does blood change color? A report from West Texas A&M University says that objects generally reflect a variety of wavelengths of light, and that blood absorbs most colors and reflects light mainly in the red spectrum, as we have already noticed.
However, blood also reflects an amount of green and blue light (less than red, yes, but still). The researchers argue that "objects do not have an intrinsic color" and, instead, the color of an object is determined by three factors: the color content of the incident light that illuminates the object, the way the object reflects, absorbs and transmits the incident colors of light and the way the eye interprets the colors of the light coming from the object.
Green blood in the sea
The study, which was published in Applied Spectroscopy, found that if you use a light source containing all the visible colors except red and shine it on the blood, the blood will be green.
"First of all, without the presence of red light, blood cannot reflect any red light. The only thing left that can reflect is green light. The blood is therefore green. This is not a trick of the eye. Blood is literally green. Normally, we don't notice the green color of blood because there is usually much more red light being reflected," says the study. In the video below, we see this in practice:
Following this line of reasoning, what happens in the ocean is that the water is naturally "bluish" because it absorbs some of the red light. The deeper we go into the ocean, the less red light there is. "Without the red color in sunlight, only green light is reflected in the blood," the authors explain.
So you have to understand that the blood doesn't change when it's at the bottom of the sea. Instead, the green color of the blood that is always present becomes more noticeable in these conditions. We can conclude that blood turns green whenever there is a light source with no red color, and not just in the depths of the ocean.
