In fluorometry, the wavelength of light emitted by a substance is typically:

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In fluorometry, emitted light has a longer wavelength than what was absorbed because part of the absorbed energy is lost as heat during relaxation in the excited state before emission. After photon absorption, the molecule quickly relaxes to the lowest vibrational level of the excited electronic state; when it returns to the ground state, it emits a photon with lower energy than the absorbed one. Since energy and wavelength are inversely related (E = hc/λ), this lower energy emission corresponds to a longer wavelength. This shift, known as the Stokes shift, is the hallmark of ordinary fluorescence. The other possibilities would require emitting with the same or higher energy without loss, which isn’t typical for fluorescence, and an unrelated wavelength would ignore the energy relationship between absorption and emission.