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Fluorescent (Fluo), Night Diving, is a “new” approach to night diving that is becoming very popular. Divers are taking a new look at familiar dive sites in a new light. On a fluo dive, you use a “blue light” to illuminate features of the dive site.

Fluorescent night diving is a whole new experience

When viewed with a yellow filter, the items seem to glow but with colors unlike those seen by the naked eye in daylight or at night with a normal dive light.You will see something entirely different, the colors and complexity can be overwhelming.

The marine life that might seem dull and gray during the day might look like a riot of colors at night. A pale yellow piece of coral is now fire red and a glowing beauty of form and color.

Also read: Here is Why You Should Never Touch Marine Life

If you were a teenager in the 60s, you might think “groovy man, groovy”.

If so, you probably had "black lights" and black light posters in your room if your parents allowed it. Under the black lights, the posters glowed with strong colors.

A very good poster might even have a completely different image than the one seen in normal room light because the items response with a light in a slightly higher wavelength. The black lights of the 70's are just another term used for Ultraviolet (UV) light, which is a shorter wavelength than that our eyes normally see.

When the posters were illuminated by the short wavelength in the absents of other lights, we can see the reaction. This is the same as what we see on fluor night dives. When you think that divers who grew up in the 70's are the ancients, here is another popular cult use of UV light, CSI.

There are dozens of television shows centered around the process of Crime Scene Investigation. They always have someone walking around with a special flashlight with either a filter above it or they are wearing strange sunglasses. They are using a UV light and a filter, to see items emitting light that are not visible in normal light. Blood does that very well.

These same concepts are what you will experience when we you go night diving with fluorescent lights. Note, that fluorescent diving is also sometimes called UV diving. That is because our most common interaction with fluorescence, is in the realm of the UV. The “blue light” used in this type of diving is slightly longer than the wavelength of the UV range.

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UV is from 200-400 nanometer (nm), visible light from 400- 760 nm, and infrared starts at the 760 nm going longer. The “blue light” used in fluorescence diving is at the very end of the visible spectrum, between 400 and 470 nm depending on the manufacturer. A few lights are in the UV range of 350-400 nm, which is the range of the old fashion “black lights”.

When you go out for a fluo night dive, you probably will use a mask with a yellow filter, this filter is similar to what CSI's use, which will help enhance the image. It is also said the filter helps reduce the strain on the eyes trying to focus on just the narrow range of visible light.

Fluorescence vs. Phosphorescence vs. Bioluminescence

Like may aspects of our ocean, science does not have a full understanding of the fluorescence of marine life. However, they can see patterns. Marine species (like corals) that have a fluorescence to them often have a range of colors that are similar to different members of that species.

Scientist have started using blue lights to help judge the health of a reef. The color difference in one portion of a reef might indicate a sickness or the starting of a bleaching event.

Reef destroying algae might be taking over a reef but might not be visible to the naked eye in daylight, under the blue light the algae are bright red. Dying sections of coral would have little or no color.


While fluor night diving there are three terms, you may come across.

Here are some properties of light sources under water that you might encounter.

Also read: 5 Reasons Why Night Diving Is More Fun

Fluorescence: This one differs from the other two because of the short duration. The colors that are seen are in part the response of the light shining on them. They are responding to a low-frequency range and low intensity.

Using a broader range such as a “white” light that covers the full visible range will overpower the fluorescence. It is always there but only visible to us in the right conditions. The fluorescence requires the light to be visible and while the potential is there, it only visible in the light.

Phosphorescence: Phosphorescence occurs in many species, often seen among glowing floating algae masses. It is the old glow in the dark process. Sunlight “charges” the algae that they use in their metabolism. As they used the stored energy, a portion of it is converted to light.

Bioluminescence: Bioluminescence is caused by a chemical reaction within the animal that causes it to glow. Many deep sea creatures have this trait as do fireflies. It is also common on many forms of plankton.

When they come in contact with something, they glow briefly. They are often the cause of the glow of a ship's wake. Night divers will marvel at the lights that flash along their hand as they move it through the water.

Also read: What is Bioluminescence? - Nature’s Glow in the Dark Show

Where in the world can you fluorescent night diving?

This list contains just a few of the most popular destinations in the world where you can go UV night diving.

Go with the Fluo

Night diving is an exciting and educational style of diving. Diving it with a “blue light” and filter allows us to see what some species can see without the help. Like hearing what is the normal range of visible light can be different in different species other than man. Go out and see the world under the sea.

What are your thoughts about fluorescent night diving? Have you done it before? Let us know in the comments below

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Article written by Rutger Thole who is an avid scuba diver and loves to travel, dive and write about scuba diving. Based in Amsterdam, he runs and at least twice a year he plans a dive trip of the beaten track.

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