Last updated September 29, 2014

Living Light: The Dazzling Secrets of Bioluminescence

The Glow of Life: How and Why Some Beings Produce Light?

Bioluminescence is the emission of light by a living organism. This light is not reflected light but produced light. Thousands of animal species emit light (bacteria, fungi, algae, insects, mollusks, crustaceans) and especially deep-sea fish that live in the abyss.

In the Abyss, bioluminescence is common since 95% of individuals, collected at 4,000 meters deep, are luminous. Bioluminescence is an integral part of the survival means of these species. These animals trigger chemical reactions during which energy is converted into light energy.

Bioluminescence produces a cold light less than 20% of the light generates heat (very little loss in energy conversion). Bioluminescence is produced thanks to the oxidation of a molecule (Luciferin) in the presence of a catalyst enzyme Luciferase.

Bioluminescence differs among animals. It is mainly in the marine world that a great variety of luminous animals are found. In particular, in the abyss, where sunlight does not reach (at least 80% of species are bioluminescent).

Firefly squid (Watasenia scintillans) – Emits intense blue flashes.
Crystal jellyfish (Aequorea victoria) – Source of the GFP protein (Green Fluorescent Protein, but initially emits blue light).
Bioluminescent plankton (Dinoflagellates like Noctiluca scintillans) – Creates blue-green luminous waves.
Lanternfish (Myctophidae) – Bluish photophores for camouflage and communication.
Deep-sea dragonfish (Malacosteus niger) – Produces red light thanks to a special pigment, allowing it to illuminate its prey without being seen.
Some abyssal squids (Stigmatoteuthis) – Emit red or purple glows.
Glow-worm (Lampyris noctiluca) – The female emits a yellow-green light to attract males.
Some marine worms (Polychaetes like Odontosyllis) – Produce yellow luminous trails during reproduction.
Atolla jellyfish – Some emit a golden glow in addition to blue.
Mycena chlorophos (Tropical mushroom) - Emits a green glow in the dark, probably to attract insects and disperse its spores.
The squid Heteroteuthis dispar – Emits both blue and green light.

A Weapon, a Lure, a Masterpiece of Evolution

The secrets of natural bioluminescence

The very particular conditions that reign in the great depths have favored the development of a fauna totally different from that encountered on the surface. Beyond 100 meters, in cold and dark waters, plants disappear. Life in the deep sea is exclusively animal.

Bioluminescence is a multifunctional tool, sculpted by evolution to meet the challenges of life in darkness. The darkness of the abyss explains the large number of blind species or, conversely, species with very large, hypertrophied, and often bulbous eyes allowing them to capture the slightest light flux. Bioluminescence phenomena are particularly developed in deep-sea fish and cephalopods. Some possess organs capable of emitting light, the photophores. Fish carry lures, on the flanks, on the head, or at the end of appendages serving as lamps.

Bioluminescence plays various essential roles in the survival, reproduction, and ecological interactions of many organisms.

Defense & Protection: Some squids (like Heteroteuthis) eject a cloud of bioluminescent mucus to distract predators. Ostracods (small crustaceans) emit light flashes to attract secondary predators, creating a diversion.
Reproduction & Communication: Fireflies use specific light signals (flashes, rhythms) to attract a mate. Some marine worms (like Odontosyllis) synchronize their emission of green light during full moon "nuptials."
Hunting & Trap: The abyssal dragonfish (Malacosteus) uses red light (invisible to most prey) to illuminate its prey without giving itself away. The abyssal anglerfish (Melanocetus) has a "lure" (an appendage with bioluminescent bacteria) to attract fish.
Social Communication: Dinoflagellates (plankton) emit blue light in a cascade to alert the group in case of threat ( "luminous wave" effect). Some polychaete worms synchronize their bioluminescence to form luminous swarms during reproduction.
Mimicry & Deception: The vampire squid (Vampyroteuthis infernalis) produces bioluminescent glowing filaments to mimic jellyfish and repel predators.
Unknown or Secondary Functions: Regulation of oxidative stress (the bioluminescence reaction could eliminate cellular waste). Symbiosis with bacteria (as in the bobtail squid, which cultivates luminous bacteria for its camouflage).

Human Bioluminescence: An Infinitesimal Light

Unlike fireflies or abyssal creatures, humans do not have visible bioluminescence, but our body emits an ultra-weak light, linked to biochemical reactions.

Humans emit light (infrared light) 1000 times weaker than the sensitivity of the naked eye, with a peak around 4-5 pm (linked to metabolism). Certain areas (like the face) emit more light, probably due to increased metabolic activity.

Understanding this light could help study cellular metabolism. Abnormal light emission could signal increased oxidative stress possibly related to cancer, diabetes, or simply aging.