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How do deep-sea fish use photophores to hide from predators below them?

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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.

Deep-sea fish use photophores—specialized light-producing organs—to hide from predators through a process known as countershading.12

In the twilight zone of the ocean, predators often hunt by looking upward to spot the silhouettes of potential prey against the faint light filtering down from the surface. To avoid detection, many deep-sea fish, such as lantern fishes and hatchetfishes, possess photophores arranged along their ventral (lower) surfaces.21

These organs emit light downward and outward, allowing the fish to match the intensity of the sunlight penetrating from above. By effectively "filling in" their own shadow, the fish obliterates its silhouette, making it blend into the ambient light and becoming nearly invisible to predators lurking below. This biological mechanism is a highly effective form of deceptive coloration, ensuring the survival of the organism in a light-limited environment.12