Why are most photos taken underwater blue?

Most photos or movies taken underwater are blue, which is due to the selective absorption of seawater-some colors of light are absorbed, while others cannot spread. White light is a mixture of red, orange, yellow, green, blue, indigo and violet light with different frequencies. When it shines on an object, some colors of light waves are absorbed and some colors are reflected. What we usually call the color of an object is the color of the light reflected by the object (or itself). For example, a person wearing a red shirt mainly reflects red light, and most other colors are absorbed. In air, light waves of different colors travel together at the same speed, but not in water. Water absorbs some wavelengths of light, but not all of it. It absorbs red light better. Sunlight shot into the sea less than 20 feet from the air, and all the red light was absorbed. Then there are orange and yellow lights, which also travel less than 40 and 70 feet in seawater. After 75 feet, only blue light is left, and all other colors of light are absorbed, which is why all underwater photos taken with sea light are blue. After using special light sources, underwater photographers can also have a panoramic view of the colorful underwater world. When shooting, they put the light source as close as possible to the object to shorten the distance of light propagation under water, reduce selective absorption and expose the true color of the object.

The underwater world is mostly dark. At noon, the sun shines directly, and the light easily penetrates the water. Others, such as early morning and evening, are oblique light, most of which are reflected by the water surface, and the underwater light is much darker than the water light. The best time for light to penetrate water is from 10 am to 2 pm. In addition to being absorbed by water, the light passing through water will be absorbed and reflected even if there are very few trace impurities and microorganisms (such as plankton) in the water, which is difficult for human eyes to distinguish. In some areas, due to their influence, underwater visibility becomes extremely low, and it is difficult to identify a medium-sized object at close range.

Blue light can only be transmitted above 100 meters underwater. At a depth of 200 meters, it is already opaque. At the depth of1700m, the photographic film will not be exposed after two hours. It is already deep in the sea, far from the sun, and it is dark all year round. Although the sun can't reach here, there are all kinds of luminous creatures (the brightness is of course very weak). Jellyfish is like a firefly candle at night, and Ran Ran swims; Huge, silver-shield-shaped molars, looming, swim on the sea curtain, showing a wonderful landscape of green, yellow, blue, white and red; The squid in the 3 km deep sea of the Indian Ocean emits three kinds of light at the same time: the two luminous points on the anus emit rust-colored red light, the abdomen emits blue light, and the eyes emit blue light; Nocturnal insects resembling small ping-pong balls emit blue-green light; The brightness of golden-eyed snapper is equivalent to a flashlight with insufficient power. With its light, the hands and dial of a watch two meters away can be clearly recognized in the dark. At night, frogmen in the sea can see the light from the hidden snapper at a distance of 15 meters. According to incomplete statistics, there are more than 20 species of photobacteria 10, and other marine animals have 10 phylum, 35 orders, including protozoa, echinoderms, molluscs and fish. The light emitted by marine life is called cold light. So far, scientists haven't fully figured out why these creatures have no fire when they light up and no heat when they shine.