Knowledge: Underwater Fluorescence FAQ

There are a number of questions that come up all the time about underwater fluorescence and the equipment needed to view and photograph it. Read on for answers to many of these questions, and please contact us to suggest other questions we should be answering!


What is fluorescence?

Fluorescence is the name for the absorption of light at one wavelength and its re-emission at another wavelength. What that boils down to is that some things will glow when you shine the right light on them. The ‘right light’ can be different for different targets. We are most used to seeing fluorescence produced by ultraviolet light, often called ‘black light’ because we humans can’t see it. At NIGHTSEA we mostly deal with specially filtered blue lights, because the blue has proved to be better at making most things underwater fluoresce. See the article explaining Why NIGHTSEA uses blue light for underwater fluorescence.

Fluorescence is kind of magical. You point one light at a target and a totally different color comes out. One of the characteristics of fluorescence is the intense, highly saturated colors. We are used to seeing things illuminated by white light, which contains all the colors of the spectrum. When something fluoresces it usually emits only a narrow range of colors, making it appear like a pure color.

There are fluorescent items around you all the time. Highlighter  pens, orange traffic cones and safety vests, and bright plastics for children’s toys are just a few examples of the way fluorescence is used. The fluorescence of these products is what makes them appear especially bright. Just shine your NIGHTSEA light around you and see what lights up!

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Does NIGHTSEA sell fluorescent lights?

No. Fluorescent lights are what you commonly find in office buildings, and are called that because they produce much of their light by the process of fluorescence (see the answer to the previous question). NIGHTSEA develops equipment – light sources and add-on filters for your electronic flash – that causes undersea subjects to fluoresce. The NIGHTSEA lights themselves are not fluorescent.

For more information see our article on Fluorescent light vs. a light that excites fluorescence.

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Do the NIGHTSEA lights emit ultraviolet light?

NIGHTSEA’s lights are designed to emit a carefully controlled range of blue, not ultraviolet, wavelengths. We started out with ultraviolet a long time ago, but with a combination of science and experiment learned that blue provides a far superior experience. There are some things that fluoresce under UV but not blue, but overall more things fluoresce, and fluoresce more brightly, when illuminated with the right blue light and viewed through the yellow barrier filter.

For more information see our articles explaining Why NIGHTSEA uses blue light for underwater fluorescence and The role of the barrier filter in fluorescence viewing and photography.

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I’ve seen things glow when I dive at night. Is that fluorescence?

Just about everyone who has dived at night has seen little flashing lights in the water. Usually this comes from single-celled organisms, called dinoflagellates, but there are a number of marine critters that can make their own glow. They produce light by a chemical reaction called bioluminescence, the same way that fireflies light up. Most emit light when physically disturbed, and the motion of your body through the water can set them off.

Bioluminescence and fluorescence are both forms of luminescence. A big difference between them is that for fluorescence you have to stimulate the glow by shining a light on the subject, while for bioluminescence everything needed to glow is already contained in the organism. The corals and other subjects pictured on this Web site are not bioluminescent, and you need to use the right light to make them fluoresce.

For more information on bioluminescence, check out the web site at UC Santa Barbara. To see some beautiful photographs of bioluminescence in Bioluminescent Bay, Vieques, Puerto Rico, visit www.biobay.com.

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What can you expect to see with NIGHTSEA lights?

Not everything fluoresces, but fluorescence is everywhere. When you dive with lights to excite fluorescence you will be working in the dark. As you move the beam around you will often see nothing, but suddenly something will light up. It might be a coral or anemone, a shrimp or a nudibranch, a tunicate or a bristleworm. Or it might be a new fluorescence that has never been described before.

Some things will fluoresce brightly and you will be able to spot them from a distance. Others will not fluoresce as strongly and you will need to get up close to them. And still others will not respond at all.

Sometimes all of an organism fluoresces with one color, sometimes there are mixed colors and intensities. Sometimes only a small part of a creature fluoresces and you have to turn on your white light to find out what you are looking at. Some dives may be disappointing, while others will be rich in new observations. You will be looking for something that has not been explored in detail, and you will be helping to add to our store of knowledge on the subject.

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Do you have to dive at night to see fluorescence?

Not necessarily, but if you don’t you will be missing a lot. As far back as the 1950’s divers noticed that some corals and anemones either appeared very bright or had colors that should have been impossible. Water absorbs reds and oranges first, and at 60 feet (20 meters) there shouldn’t be orange corals, but there are. The corals are absorbing ultraviolet and blue light and turning it into orange.

But the corals that are obviously fluorescent in daylight are just a small minority. Many specimens that look completely ordinary in daylight or when illuminated with a normal dive light will light up with remarkable colors when you shine the NightSea lights on them. In some cases some individuals will fluoresce brightly, while other specimens of the same species won’t react at all. The reasons for this kind of variation aren’t known yet.

If you try to use lights to stimulate fluorescence in the daytime the results will be disappointing. Fluorescence is a weak effect and the ambient light will usually overwhelm it. You will have some success if you look under overhangs, inside crevices, or other dim places, but to see fluorescence in its best light you should dive at night.

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Where can I learn more about underwater fluorescence?

We have put together a list of references to publications, both general and scientific, about fluorescence in marine organisms. There is also a brief history of underwater fluorescence on this web site.

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