Is it ensure, insure, or assure?
fluorescence fluo·res·cence (flu-rěs'əns, flô-)
The emission of electromagnetic radiation, especially of visible light, stimulated in a substance by the absorption of incident radiation and persisting only as long as the stimulating radiation is continued.
The property of emitting such radiation.
The emission of light from an object as a result of bombardment by other kinds of electromagnetic radiation, such as x-rays or ultraviolet rays. Fluorescent materials may appear one color when bathed in visible light and another color when exposed to other kinds of electromagnetic radiation.
Note: “Black light” depends on fluorescence for its effects.