Bioluminescence and Fluorescence Underwater: The Science and How to Photograph It

Imagine descending into total darkness on a night dive. Your light is off. You wave your hand through the water and a galaxy of blue sparks erupts around your fingers. Below you, corals glow neon green and orange as if plugged into some invisible power source. A comb jelly drifts past, its rows of cilia refracting light into shimmering rainbows. The ocean, it turns out, has been running its own light show for hundreds of millions of years — and most divers have barely scratched the surface of what is possible to see and photograph down there.

This guide covers the two distinct phenomena behind the ocean's glow — bioluminescence and fluorescence — explains the science in plain language, tells you where to witness each one, and walks you through the camera settings and gear you need to capture both on your next dive.

Bioluminescence vs. Fluorescence: The Key Distinction

Before you pack your gear bag, you need to understand that bioluminescence and fluorescence are fundamentally different processes. Confusing them is the single most common mistake divers make when planning a "glow dive," and it leads to bringing the wrong equipment.

Bioluminescence: Living Light

Bioluminescence is light that an organism produces on its own through an internal chemical reaction. The basic recipe is remarkably consistent across the animal kingdom: a light-emitting molecule called luciferin reacts with an enzyme called luciferase in the presence of oxygen and ATP (cellular energy). The reaction releases energy as visible light — typically blue or green, because those wavelengths travel farthest through seawater.

No external light source is needed. A bioluminescent creature can glow in total darkness. Think of dinoflagellates sparkling when waves disturb them, or an anglerfish dangling its glowing lure in the abyss.

Fluorescence: Borrowed Light, New Colors

Fluorescence is a completely different mechanism. A fluorescent organism absorbs light at one wavelength (typically blue or ultraviolet) and re-emits it at a longer wavelength — shifting blue light into vivid greens, oranges, and reds. The organism is not generating its own light; it is transforming light that already exists.

This is why fluorescence is invisible under normal white-light diving conditions. You need a specific blue or UV excitation light to trigger the effect, plus a yellow barrier filter over your eyes (or camera lens) to block the reflected blue and reveal only the fluorescent glow beneath.

Why This Matters for Divers

The practical takeaway is simple:

• To see bioluminescence, you need darkness. Turn off all lights. Let your eyes adapt. Any white light will wash out the effect.
• To see fluorescence, you need a blue/UV excitation light and a yellow barrier filter. Darkness alone will not reveal it.

Different phenomena, different gear, different techniques. The rest of this guide treats each one separately.

The Science Behind the Glow

How Bioluminescence Works

The luciferin-luciferase reaction is one of nature's most successful inventions. According to NOAA Ocean Explorer, bioluminescence has evolved independently at least 40 separate times across the tree of life — in bacteria, fungi, fish, jellyfish, squid, worms, and crustaceans. That level of convergent evolution tells scientists that producing light confers enormous survival advantages in the deep ocean, where sunlight never reaches.

Why do organisms glow? The reasons fall into four broad categories:

• Defense: Many creatures use sudden flashes to startle predators. Some deep-sea shrimp vomit bioluminescent fluid to confuse attackers — the underwater equivalent of a smoke bomb. Others, like certain squid, release glowing ink.
• Hunting: The anglerfish's bioluminescent lure is iconic, but it is far from unique. Cookie-cutter sharks use ventral bioluminescence to mimic the silhouette of smaller fish, tricking predators from below while attracting curious prey from above.
• Communication: Firefly squid (Watasenia scintillans) use complex light patterns to find mates. Ostracods — tiny crustaceans — produce bioluminescent trails in the water column as courtship displays, creating underwater constellations.
• Camouflage (counterillumination): Many midwater species produce light on their undersides that matches the faint sunlight filtering from above, eliminating their silhouette so predators below cannot spot them.

How Fluorescence Works

Fluorescence relies on special proteins that absorb high-energy photons (short-wavelength blue/UV light) and re-emit lower-energy photons (longer-wavelength green, orange, or red light). The most famous of these is Green Fluorescent Protein (GFP), originally isolated from the crystal jelly Aequorea victoria.

GFP became one of the most important tools in modern biology. Scientists use it to tag individual proteins inside living cells and watch biological processes in real time under a microscope. The discovery was so transformative that Osamu Shimomura, Martin Chalfie, and Roger Tsien shared the 2008 Nobel Prize in Chemistry for their work on GFP — a molecule that was first found glowing quietly on a jellyfish in the Pacific Northwest.

Why marine organisms fluoresce is still debated. Leading hypotheses include UV protection (fluorescent proteins may convert damaging UV radiation into harmless visible light), prey attraction, communication between individuals of the same species, and enhanced photosynthesis in symbiotic algae within coral tissue.

Which Creatures Glow?

Bioluminescent Species Divers Can See

• Dinoflagellates: Single-celled plankton responsible for the famous "glowing seas." Disturb the water and they flash blue. Entire bays can light up.
• Comb jellies (ctenophores): Their rainbow shimmer is actually light diffraction, not bioluminescence — but many species also produce true bioluminescent flashes when disturbed.
• Flashlight fish: Small reef fish with bioluminescent organs beneath their eyes. They use a rotating "shutter" of skin to flash their lights on and off.
• Anglerfish: Deep-sea predators with bioluminescent bacterial lures. Rarely seen by recreational divers, but an icon of the deep.
• Firefly squid (Watasenia scintillans): Covered in photophores, these squid light up the surface waters of Toyama Bay, Japan, each spring in one of the ocean's greatest spectacles.
• Ostracods: Tiny seed-shrimp that produce luminous trails during mating displays — visible on Caribbean night dives if you know where to look.

Fluorescent Species Divers Can See

• Hard corals: The majority of reef-building coral species contain fluorescent proteins. Under blue light, an ordinary brown coral head can transform into an electric green or orange beacon.
• Anemones: Many species fluoresce brilliantly, often in green or pink.
• Scorpionfish: Some species display striking red fluorescence — potentially used for camouflage against fluorescent algae backgrounds.
• Nudibranchs: Certain species exhibit fluorescence, though it varies widely. Fluoro diving is a fantastic way to spot nudibranchs you would otherwise miss.
• Juvenile fish and eels: Larval and juvenile stages of some species are strongly fluorescent, possibly as a form of UV protection in shallow nursery habitats.

Where to See It

Bioluminescence Hot Spots

• Mosquito Bay, Vieques, Puerto Rico: Recognized by Guinness World Records as the brightest bioluminescent bay on Earth. Dinoflagellate concentrations here are extraordinary.
• Toyama Bay, Japan: Every March through June, millions of firefly squid rise to the surface to spawn, turning the bay into a galaxy of blue light.
• Maldives (Vaadhoo Island and others): Seasonal dinoflagellate blooms create glowing shorelines — the famous "sea of stars."
• San Juan Island, Washington, USA: Bioluminescent plankton blooms light up kayaking and night diving from late summer into fall.

Fluorescence Diving (Fluoro Diving)

The good news about fluoro diving is that you do not need to travel to a specific destination. Almost any tropical or subtropical reef with healthy coral cover will produce spectacular fluorescence. Popular fluoro diving locations include the Red Sea, Bonaire, the Philippines, Indonesia, and Australia's Great Barrier Reef. Many dive centers now offer dedicated fluoro night dives with blue light and filter rentals.

For the best fluorescence, look for reefs with high coral diversity. The more species present, the more varied the fluorescent color palette — greens, oranges, reds, and even rare blues.

How to Photograph Bioluminescence

Photographing bioluminescence is one of the most challenging — and rewarding — types of night dive photography. The light output is extremely faint, which means your camera needs to gather as much light as possible. Here is how to set up for success.

Camera Settings

• ISO: High. Start at ISO 1600 and increase to 3200 or 6400 as needed. Modern smartphone sensors handle high ISO surprisingly well.
• Shutter speed: Slow. Start at 1/30 second and experiment down to 1 second or longer for static scenes. For moving subjects like dinoflagellate trails, 1/15 to 1/4 second captures the streaks beautifully.
• Aperture: Wide open. Use the widest aperture your lens offers (lowest f-number) to maximize light intake.
• White balance: Set manually. Auto white balance struggles in monochromatic blue light. Try a custom setting around 5500-6500K.

Critical Gear and Technique Tips

• No strobe or flash. A strobe blast will instantly overpower the faint bioluminescent glow and ruin the shot. Keep your strobe off entirely.
• Use red light for navigation. Red wavelengths do not trigger or wash out bioluminescence the way white light does. A red-filtered dive light lets you see where you are going without disturbing the show.
• Stabilize yourself. With slow shutter speeds, camera shake is your enemy. Brace your elbows against your body, exhale slowly, and shoot between breaths. If shooting in open water, achieve neutral buoyancy and stay still — never brace against coral or marine life.
• Shoot video too. Modern phones in night mode can record bioluminescence that your eyes can barely perceive. A time-lapse of dinoflagellates sparkling around you can be stunning.

Why Smartphones Work for Bioluminescence

Here is something that surprises many photographers: modern smartphones are increasingly capable bioluminescence cameras. Night modes on recent iPhones and Android flagships use computational photography — stacking multiple exposures and applying AI-based noise reduction — to capture scenes that would have required a dedicated camera and tripod just a few years ago.

Paired with a quality underwater phone housing like the SeaTouch 4 Max, you get full touchscreen control at depth — critical for adjusting exposure on the fly in unpredictable low-light conditions. The DIVEVOLK housing's responsive touch interface means you can switch to night mode, tap to focus, and adjust exposure compensation without fumbling with buttons in the dark.

How to Photograph Fluorescence

Fluorescence photography is technically easier than bioluminescence photography because you are supplying the excitation light yourself, which gives you control over the scene's brightness. The challenge is in the filtration — you need to isolate the fluorescent light from the overwhelming blue excitation light.

Essential Gear

• Blue or UV excitation light: This is non-negotiable. You need a dedicated blue light (typically 450-470nm wavelength) to trigger fluorescence in marine organisms. Some dive lights like the SL20 can be paired with blue filter accessories, though dedicated fluoro lights are ideal for serious fluorescence photography.
• Yellow barrier filter over the lens: This filter blocks the reflected blue excitation light and passes only the longer-wavelength fluorescent emissions. Without it, your images will be overwhelmed by blue light and the fluorescence will be invisible. Clip-on yellow filters are available for phone housings and are an affordable entry point.
• Mask filter: A yellow filter over your dive mask lets you see the fluorescence with your own eyes while diving. This is not required for photography, but it transforms the experience.

Camera Settings for Fluoro Photography

• ISO: Moderate. ISO 400-800 is usually sufficient since the excitation light provides reasonable brightness.
• Shutter speed: Normal range. 1/60 to 1/125 second works for most stationary subjects. Slow down for wider scenes.
• Aperture: f/5.6 to f/8 for good depth of field. You have more light to work with than bioluminescence, so you can stop down.
• White balance: Manual or custom. Auto white balance will try to "correct" the fluorescent colors and desaturate them. Lock in a custom white balance or shoot in RAW for maximum post-processing flexibility.

Composition Tips

• Dark backgrounds are your friend. Position your excitation light so the fluorescent subject is brightly lit against a dark water background. This contrast is what makes fluoro images so striking.
• Get close. Fluorescence photography rewards macro and close-up compositions. Individual coral polyps, anemone tentacles, and nudibranchs all reveal incredible detail under fluorescent light. A macro lens attachment paired with your phone housing takes this to the next level.
• Explore the full reef. Sweep your blue light slowly across the reef and watch for unexpected fluorescence. Species that look dull under white light can explode with color under UV/blue excitation — this element of surprise is part of what makes fluoro diving addictive.

The Budget-Friendly Phone Approach to Fluoro Diving

One of the best things about fluorescence photography is that you do not need a $5,000 camera rig to get publishable results. A smartphone in a DIVEVOLK SeaTouch 4 Max kit with a clip-on yellow barrier filter and a handheld blue excitation light is a genuinely effective fluoro photography setup — and it fits in a carry-on.

The SeaTouch 4 Max gives you full access to your phone's camera app, including manual exposure controls through apps like UWACAM. You can lock focus, adjust ISO, and fine-tune shutter speed — all through the housing's touchscreen. For anyone looking to try fluoro diving without committing to dedicated camera gear, this is the most accessible path into the hobby.

Responsible Glow Diving: Protecting What We Photograph

Both bioluminescent and fluorescent organisms are part of fragile marine ecosystems. As Mission Blue and other ocean conservation organizations emphasize, responsible observation means minimizing your impact.

• Never touch fluorescent corals to "test" if they glow. Coral tissue is extremely delicate, and even brief contact can damage or kill polyps.
• Do not chase or harass bioluminescent creatures. Repeatedly disturbing an organism to trigger its bioluminescent response causes stress. Observe, photograph, and move on.
• Maintain neutral buoyancy at all times. Night dives and fluoro dives often involve hovering close to the reef in low visibility. Perfect your buoyancy before attempting these specialized dives. PADI offers advanced buoyancy courses that are excellent preparation.
• Follow the golden rule: Take only photos, leave only bubbles. The underwater light show has been running for millions of years. Our job is to witness it — not to interfere with it.

Gear Checklist: What to Bring

Here is a quick reference for both types of glow diving:

If you are new to underwater photography or need help choosing the right housing and accessories for glow diving, DIVEVOLK's technical support team can help you match gear to your specific phone and diving goals.

The Ocean's Oldest Light Show

Bioluminescence and fluorescence are not novelties — they are ancient adaptations, refined over hundreds of millions of years of evolution. The chemical machinery of bioluminescence predates the dinosaurs. Fluorescent proteins in corals may have been glowing since before the first fish grew legs and walked onto land.

What has changed is our ability to see and share these phenomena. A generation ago, photographing bioluminescence required professional-grade equipment, manual film cameras, and considerable expertise. Today, a smartphone in a waterproof housing can capture images that would have been impossible outside of a National Geographic expedition. Fluoro diving, which barely existed as a recreational activity 15 years ago, is now offered at dive centers worldwide.

The ocean's light show has been running for millions of years. The blue spark of a dinoflagellate, the neon glow of a fluorescent coral, the ghostly lure of an anglerfish — they are all still there, every night, on every reef, in every ocean. All you need is the right tools and the willingness to descend into the dark.