( ( Fluorescence ( of ( a substance ) ) ) ( ( is ( seen ( when ( ( the molecule ) ( is ( exposed ( to ( ( ( ( a ( specific wavelength ) ) ( of ( light ( -LRB- ( ( excitation ( ( wavelength or ) spectrum ) ) -RRB- ) ) ) ) ) and ) ( ( the light ) ( it ( emits ( -LRB- ( ( the ( emission ( ( wavelength or ) spectrum ) ) ) ( -RRB- ( ( is always ) ( of ( a ( higher wavelength ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Fluorescence)) (PP (IN of) (NP (DT a) (NN substance)))) (VP (VBZ is) (VP (VBN seen) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NN molecule)) (VP (VBZ is) (VP (VBN exposed) (PP (TO to) (NP (NP (NP (DT a) (JJ specific) (NN wavelength)) (PP (IN of) (NP (NP (NN light)) (PRN (-LRB- -LRB-) (NP (NNS excitation) (NN wavelength) (CC or) (NN spectrum)) (-RRB- -RRB-))))) (CC and) (NP (NP (DT the) (NN light)) (SBAR (S (NP (PRP it)) (VP (VBZ emits) (SBAR (S (-LRB- -LRB-) (NP (DT the) (NN emission) (NN wavelength) (CC or) (NN spectrum)) (-RRB- -RRB-) (VP (VBZ is) (ADVP (RB always)) (PP (IN of) (NP (DT a) (JJR higher) (NN wavelength)))))))))))))))))) (. .)))
Fluorescence of a substance is seen when the molecule is exposed to a specific wavelength of light (excitation wavelength or spectrum) and the light it emits ( the emission wavelength or spectrum) is always of a higher wavelength.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (VP (VBN exposed) (PP (TO to) (NP (NN ultraviolet)))))) (, ,) (NP (NP (DT some) (NNS substances)) (, ,) (PRN (PP (JJ such) (IN as) (NP (NP (NNS minerals)) (, ,) (ADJP (NN glow) (PP (IN in) (NP (ADJP (JJ characteristic) (JJ visible)) (NNS wavelengths))))))) (, ,) (PP (IN in) (NP (DT a) (NN process)))) (VP (VBD called) (ADJP (JJ fluorescence))) (. .)))
When exposed to ultraviolet, some substances, such as minerals, glow in characteristic visible wavelengths, in a process called fluorescence.