fluorogen

A fluorogen is a special substance that glows or "fluoresces" when it is exposed to certain types of light. In its unactivated state, it doesn't emit any light, but when it binds to a specific target or is exposed to specific wavelengths, it produces a bright, visible glow. This property makes fluorogens useful in scientific and medical research, such as tracking molecules or cells, because they can illuminate and reveal details that are otherwise hard to see. Essentially, fluorogens act as external lights, helping researchers visualize processes at the microscopic level.