The color red can be subjective with respect to the animals and plants we keep in our home aquaria. One person’s red is another’s brown, pink, orange, ginger… But this primary color is interesting for many other reasons.

Electromagnetic radiation in the wavelengths that we can see is known as the visible spectrum. Who doesn’t remember Roy G. Biv? Red sits on the edge of this spectrum, with the longest wavelengths at 620–750 nm and frequencies of 480-405 THz. Wavelengths beyond this limit are called infrared, and cannot be seen by the naked human eye. These properties, along with those of water itself, are the reasons that red light is absorbed by ocean water about 100 times more than blue light. Many creatures of the deep take advantage of this phenomenon, and have brilliant red coloration. In their natural habitat, they appear black. Anyone trying to take photographs while diving is also very familiar with the lack of red light penetrating the ocean, resulting in a blue-green appearance to most creatures. Animals and plants only appear red if there is red light present to be reflected by various pigments.

Further reading about the color red:

Further reading about red light absorption by water: NASA - Blue Ocean

As hobbyists, we look for every kind of color to make our reef tanks more appealing. In this month's slide show, red is the color of choice and you'll note it comes in many shades and sometimes surprising places.

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Many thanks to SDguy and JessyCat77 for their assistance with this project.
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