Which statement about fluorometry is true?

• A. It relies on emission of light after excitation.
• B. It measures transmitted light directly.
• C. It does not require wavelength selection.
• D. It is unrelated to excitation.

Answer: (A)

Fluorometry relies on light emitted by a substance after it has been excited with light of a shorter wavelength. When a fluorophore absorbs energy, its electrons reach a higher energy level and then return to the ground state by emitting photons. The instrument collects and measures this emitted light, and the signal strength is related to how much fluorophore is present under proper conditions. This is why the statement about emission after excitation is true. Fluorometry also uses wavelength selection to separate the excitation light from the emitted fluorescence, using filters or monochromators. It is not about transmitted light (that’s more like absorbance or transmission measurements), and the method depends on excitation, so saying it’s unrelated to excitation isn’t correct.