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How do lanternfish use their patterns of photophores for signaling?

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time-lapse photo of fireflies — Bioluminescence Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.

Lanternfishes utilize their bioluminescence through distinct arrangements of photophores—specialized light-emitting organs—located on their bodies. Each of the more than 200 species possesses a unique pattern of these photophores, which are believed to serve as specific signals for species and sex recognition, particularly during mating.12

These photophores consist of lens-shaped, transparent scales that cover the light-emanating tissue, helping to focus and amplify the light produced by the luciferin-luciferase chemical reaction. While some lanternfishes use these light organs for signaling, many also position them on their ventral and lateral surfaces to emit light downward and outward. This specific arrangement allows the fish to match the intensity of sunlight penetrating from above, effectively concealing their silhouette from predators lurking below—a process known as counter-illumination.321