Making light sounds like a reliable way to attract attention. In the ocean, the relationship can be more surprising: light produced beneath an animal can help reduce its silhouette against the brighter water above.
This use of bioluminescence is called counterillumination. The Smithsonian’s ocean guide places it alongside other functions of biological light, including feeding, signalling and defence.
Change the imagined observer
Picture the animal from below rather than from the side. Without matching light, its body may interrupt the illumination arriving from above. The question is not merely whether the animal glows, but how that glow relates to its background from a particular direction.
A simple drawing can help: sketch an observer below, an animal above it, and the surface farther overhead. Use arrows to show the viewing direction. The diagram is conceptual, not a prediction that every glowing animal uses the same strategy.
When a photograph shows luminous spots, read the species description before assigning a function. Brightness alone cannot tell you whether a structure attracts prey, communicates, or contributes to concealment.
The interesting reversal is that visibility depends on contrast and viewpoint. Producing light and becoming conspicuous are not necessarily the same outcome.