Which statement best defines fluorescence?

Which statement best defines fluorescence?

• A. Emission of heat under mechanical stress
• B. Absorption of light without emission
• C. Emission of visible light when exposed to ultraviolet light
• D. Reflection of light with no absorption

Answer: (C)

Fluorescence is when a substance absorbs higher-energy light (usually ultraviolet) and then quickly emits light of a longer wavelength, often in the visible range. The defining feature is light emission triggered by exposure to UV light. The statement that describes emission of visible light when exposed to ultraviolet light captures this idea precisely. In fluorescence, the absorbed UV energy is re-radiated as visible photons, typically within nanoseconds after excitation. Other ideas—emitting heat under stress, absorbing light without emitting anything, or simply reflecting light without absorption—do not describe fluorescence and instead point to different phenomena.

Fluorescence is when a substance absorbs higher-energy light (usually ultraviolet) and then quickly emits light of a longer wavelength, often in the visible range. The defining feature is light emission triggered by exposure to UV light.

The statement that describes emission of visible light when exposed to ultraviolet light captures this idea precisely. In fluorescence, the absorbed UV energy is re-radiated as visible photons, typically within nanoseconds after excitation. Other ideas—emitting heat under stress, absorbing light without emitting anything, or simply reflecting light without absorption—do not describe fluorescence and instead point to different phenomena.