Fluorescence night dives, or fluoro, UV and glow dives, as they are also known, are becoming increasingly popular as more and more dive centres offer scuba divers and underwater photographers the chance to experience this unique underwater phenomenon.
There are also an increasing number of vendors offering diving equipment for use on these special dives, and the purpose of this article is to explain the basics, background, techniques and equipment associated with this interesting aspect of the underwater world.
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The basics—what is it?
Fluorescence is the capability of certain materials to absorb light transmitted on one wavelength and then emit it again nanoseconds later on a different wavelength. The phenomenon occurs in certain living organisms, various minerals and in petrified fossils.
Fluorescence should not be confused with either phosphorescence, which is the capability to store light and then emit again over time such as on the dials of our diving gear or watches, or bio-luminescence where light is produced by living organisms when they consume energy.
Underwater fluorescence is usually identified with green, and indeed it is the most common colour for reasons that will be explained, but it is also possible to see red, orange and yellow fluorescence.
—Once upon a time in Torbay…
The fluorescence phenomena is believed to have been first discovered in marine creatures back in 1927 when a certain Charles E.S. Phillips noticed some glowing anemones in a tidal pool on the beach at Torbay, in the southwest of England.
The bright green colour they were emitting caught his eye, and he took some samples back to his laboratory where he used a light source together with a filter called “Wood’s Glass“, which absorbs visible light but allows ultraviolet light to pass through, to establish that the anemones were in fact fluorescent.
Then in the 1930s, the Japanese marine biologist Siro Kawaguti established that the most common coral pigments also in marine creatures fluoresced in green, followed in 1955 when those pigments were first described and formally recognised as a protein—coining the name “Green Fluorescent Protein” or GFP.
During the late 1950s, as more people started to scuba dive, the phenomena became more widely known, and articles started to appear in publications such as Skindiver and National Geographic showing the use of “blacklight” ultraviolet underwater torches to observe it.
In 1963, Sir Arthur C. Clarke, the renowned author and diver, further popularised the phenomenon when he described his experiences with fluorescence in his science fiction novel Dolphin Island.
Probably the most well-known example of fluorescence from those early days, and one which still puzzles many to this day, are bright red anemones at depths well beyond where the colour has completely disappeared from the visible spectrum. Just ask any underwater photographer about the puzzling results from their efforts to capture an image of such anemones.
Ultraviolet and blue light 101
While it is possible to see fluorescence underwater during the day, it really is at its eerie best after dark, but you will need a light source to stimulate those proteins! For many years ultraviolet (UV), or “blacklight”—light which in not visible to the human eye because of its relatively high frequency—has been synonymous with viewing fluorescence, largely as a result of the work done by Dr Rene Catala in the late 1950s at New Caledonia’s Noumea Aquarium.
But in the early 1990s, research by Dr Charles Mazel in the cold waters of Massachusetts and the warmer climes of the Bahamas, established that blue light was much better than UV. What Mazel found was that blue light (high energy visible light with a frequency between 400 and 500nm) was much more effective at exciting those proteins to fluoresce, and he went on to start a company called NightSea in 1999, which manufactures equipment for viewing and photographing fluorescence—be it underwater or in the laboratory.
Although much more efficient than ultraviolet, there is a downside to using blue light, as the fluorescence has to be viewed through a yellow barrier filter to block out the blue light reflected back to you, which tends to overwhelm the actual fluorescence. Plus high energy visible light has been linked to age-related macular degeneration.
The yellow filter is mounted on the face mask and basically makes it safe to view the blue light induced fluorescence, while greatly enhancing the overall experience—you can see much more fluorescence with the filter than without it.
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