Physics of bioluminescence: Why is most bioluminescent light blue-green?
Light travels in waves of different shapes which are known as wavelengths. This wavelength determines the color of the light. When the waves hit our eyes, they are translated into colors by the brain depending on their wavelength. The wavelengths that human eyes can see are known as the visible spectrum. Humans can see all the colors on this spectrum as they travel through air. However, light travels differently underwater because longer wavelengths can't travel as far. Most of the bioluminescence found in the ocean is in the form of blue-green light. This is because these colors are shorter wavelengths of light, which can travel through and be seen in both shallow and deep water. Light traveling from the sun of longer wavelengths such as red light doesn't reach the deep sea. This is why many deep sea animals are red. By being red in the deep sea, animals are effectively invisible. While most bioluminescent animals emit blue green light, there are exceptions. The dragonfish has evolved to emit red light. By creating their own red light in the deep sea, they are able to see red-colored prey while other animals cannot see them. One particular species of dragonfish - the Northern stoplight loosejaw can emit a red light that has such a long wavelength that it is not visible to humans, it is infrared light.