( ( While ( it ( is wet ) ) ) ( ( the emulsion ) ( ( ( ( is ( ( swollen and ) ( thereby visible ) ) ) only ) ( to ( those ( who ( can ( see ( infrared light ) ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (IN While) (S (NP (PRP it)) (VP (VBZ is) (ADJP (JJ wet))))) (NP (DT the) (NN emulsion)) (VP (VBZ is) (ADJP (ADJP (JJ swollen)) (CC and) (ADJP (ADVP (RB thereby)) (JJ visible))) (ADVP (RB only)) (PP (TO to) (NP (NP (DT those)) (SBAR (WHNP (WP who)) (S (VP (MD can) (VP (VB see) (NP (JJ infrared) (NN light))))))))) (. .)))
While it is wet the emulsion is swollen and thereby visible only to those who can see infrared light.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (DT the) (JJ only) (NN light)) (SBAR (IN that) (S (NP (NNS people)) (VP (MD can) (VP (VB see) (NP (JJ visible) (NN light))))))) (. .)))