Why do some squid release glowing clouds or mucus when threatened?

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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.

Some species of deep-sea squid release glowing clouds of ink or mucus when threatened primarily as a defensive mechanism to confuse predators.12

This light is produced through bioluminescence, a chemical reaction where the pigment luciferin is oxidized in the presence of the enzyme luciferase. While some squids produce this light themselves, others, such as the bobtail squid, rely on symbiotic cultures of luminescent bacteria housed within specialized organs called photophores. By ejecting these luminous substances, the squid creates a distraction that can startle or disorient an attacker, allowing the squid to escape.12