A fluorescent substance is best described as which?

• A. Light energy is absorbed and converted to a longer wavelength.
• B. The emitted wavelength can be seen under normal white light.
• C. There is a long time between the absorption and emission of light.
• D. It spontaneously decays and emits light.

Answer: (A)

Fluorescence happens when a substance absorbs light energy and then re-emits light at a longer wavelength. After absorbing a photon, electrons jump to a higher energy level and quickly relax, releasing a photon with lower energy (longer wavelength). This immediate re-emission is what distinguishes fluorescence from other light-emitting processes. The description that best captures this is that light energy is absorbed and converted to a longer wavelength. The other ideas imply emission without excitation, a long delay, or emission under ordinary white light, which don’t fit how fluorescence works.