U for Ultraviolet

The sumptuous colors of corals that appear in ultraviolet light. New Caledonia.

Definition

They hide everything from us, they tell us nothing! Imagine that white light is not white but is only a particular case of electromagnetic radiation accessible to our poor eyes and in any case composed of a continuous "spectrum" of colors like the famous "rainbow ”…

Synonymes

UV | Ultraviolet radiation | Ultraviolet | Bioluminescence

Starter

We have known for a long time that living beings display colors invisible to our senses, which are revealed under certain radiations, in particular ultraviolet: The fluorescence of plant chlorophyll is thus well known; the first observation (H.Kautsky et A.Hirsch) dates from 1931. Some of the fluorescent pigments found in corals are variants of the green fluorescent protein found in some jellyfish. Roger Tsien, Martin Chalfie, and Osamu Shimomura, were awarded the 2008 Nobel Prize in Chemistry for the discovery of the fluorescent protein GFP and its use as a genetic marker.

The incredible colors of corals in fluorescence. Nouméa Aquarium – New Caledonia.

But it's only recently that night owl divers had the idea (the clever ones) of illuminating the seabed during their night dives with UV lamps. A single perverse objective: to excite fluorescent proteins! And, miracle: in front of their eyes wet with tears appeared incredible colors… It thus became possible to dive and to photograph beyond the violet to frolic (in double blind) in the unknown lands of “ultraviolet”. Finally, unknown to us because many living species, once again, are able to see and communicate with these “invisible” lights.

It must be understood that UV does not illuminate anything: Only fluorescent corals react to the excitation of ultraviolet radiation and transform this invisible energy into visible light, but of low intensity. For example, out of 400 W sent, only a few light Watts are returned. It is therefore necessary to work with high sensitivities (> 800 Iso) and at low speed, well set, which makes it difficult to photograph moving subjects.

Black light

“Yellow” and “blue” filters for lights and masks.

Through trial and error, pioneers like Paul-Henri Adoardi soon abandoned ultraviolet (too tanning for living species) for a lightweight material based on blue light. Developing from 2008 with French manufacturers dyron et Bersub 70 W LED headlights, of a specific wavelength, allowing the observation of fluorescence, and the taking of digital photos, without being in total darkness. A special yellow filter must be placed on the lens and another of the same yellow on the mask and it is in this outfit that we can dive into “Avatar”…

This is now common practice and many manufacturers like big blue offer their solutions for diving and night photography with blue lighting / yellow filter pairs.

Nouméa Aquarium – New Caledonia.

Main course

Similarly, many popular destinations around the world offer this “neon diving” activity to their customers such as Sharm El Sheikh in Red Sea, a Indonesia, to Caribbean and in fact wherever there is coral.

Still it is not necessary to be limited to these environments and to try this technique in our waters, in Atlantic, a Mediterranean sea and why not in fresh water to make beautiful discoveries!

I became aware of this story of underwater fluorescence very early on when I read a large illustrated book that was lying around at my house: Carnival under the sea. THE Dr Rene Catala, curator of the aquarium of Noumea en New Caledonia published his discoveries of the fluorescence of corals there, in 1964!

Reason for which I had decided to treat this subject in one of our “Dive Logs” shot in New Caledonia. This is how I was able to dive with the scientists of the Aquarium and discover in their laboratory the marvelous colors hidden in different species of coral. And steal some pictures. A journey within the journey…

Jaundice in the Red Sea!

My second foray into Smurfland was on the cruise north of theEgypt, at the invitation of Serge Calamian de Diving Attitude, aboard their sumptuous cruise ship. That night, in fact, the sea was studded with moving blue bubbles in the center of which divers and photographers were silently ecstatic, whose eyes we sometimes met suffering from jaundice behind their filtered masks. What a yellow laugh, in fact, but I must admit that the bottom shone with striking extraterrestrial lights and that some fish were spinning, green with fear!

Hubert Lacour from Plongimage, in blue and yellow during the cruise north of Egypt with Diving Attitude.

Dessert

Specter!

We know since 1665, following the experiences of the Italian Jesuit Francesco Maria Grimaldi, that white light is actually made up of several “bands” of different colors, resembling rainbows and other diffractions of light like those seen in waterfalls from a certain angle.

But it will be necessary to wait until 1666 and the optical works of Newton (which did not only receive apples on the head) for highlighting the “spectrum” of white light diffracted in a rainbow by a prism, the basis of spectroscopy. Nevertheless Newton will miss what seems obvious today: the existence of radiation “before” red and “beyond” violet. It is william herschel who discovered infrared in 1800 and the German physicist Johann Wilhelm Ritter, ultraviolet in 1801…

See you soon for a new definition of Scuba Bécédaire. The irreverent lexicon of diving, but not only. Because sometimes ...
And in fact not since this radiant article is the last (in the order of the writing) of this reckless series. Never again, do you hear me? Still haven't chosen the Khmer alphabet with its 74 letters! Not to mention Mandarin which would have 10 to 000 characters…

Francis Le Guen

Café

Some manifestations of animal fluorescence in this award-winning film, by Elisabeth Lauwerys.