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# How do colors change as you go deeper in the ocean?

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Diver Kendall Roberg built a small rig to film how a rainbow of ten marker caps transition from vibrant to muted as he dives to 155 feet (47 meters). Roberg made the video to share how fishing lure colors can look different underwater, but it’s also a useful demonstration of light and color for physics classes.

Watch how the marker cap colors, some fluorescent, change as they drop deeper and deeper below the ocean’s surface. Why does this happen?

“Objects in everyday life are typically illuminated by white light,” PBS Learning Media explains, “such as from sunlight or an artificial light source…”

“When light strikes an object, the object absorbs some of the wavelengths and reflects others. The wavelengths of the reflected light determine the color that the object appears. For example, a ripe red tomato looks red because when white light shines on it, the pigments in the skin of the tomato reflect red wavelengths and absorb other wavelengths. A black object looks black because it absorbs all wavelengths. In contrast, a white object reflects all wavelengths.

“Because an object can only reflect wavelengths of light that shine on it, the color of the light illuminating the object affects how the object will appear. If there are no red wavelengths shining on the tomato, then there are no red wavelengths for it to reflect. If a ripe red tomato is inside a room with only a blue light, the tomato will look black because its pigments absorb blue wavelengths…”

“Similar to the tomato example above, a red fish near the surface of the water looks red because when white sunlight strikes it, it absorbs all wavelengths except red. But deeper underwater, less red light is available to strike the fish and so it does not look as red. Very deep below the surface, where no red light reaches, the fish would look black because there is only blue light available.”

Colors become progressively less visible underwater in the order they appear in the color spectrum, with red fading first. Blue and purple are the last to change due to their shorter wavelengths and higher energy. Horizontal distance also affects color; even at a depth of 5 feet, red won’t look very red if viewed from 15 feet away.

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This video was posted 2 weeks ago.