( ( Unless ( you ( can ( see ( UV light ) ) ) ) ) ( ( -LRB- ( ( ( most people ) ( ca n't ) ) -RRB- ) ) ( UV ( ( ( is not ) visible ) . ) ) ) )
(ROOT (S (SBAR (IN Unless) (S (NP (PRP you)) (VP (MD can) (VP (VB see) (NP (NNP UV) (NN light)))))) (PRN (-LRB- -LRB-) (S (NP (JJS most) (NNS people)) (VP (MD ca) (RB n't))) (-RRB- -RRB-)) (NP (NNP UV)) (VP (VBZ is) (RB not) (ADJP (JJ visible))) (. .)))
Unless you can see UV light (most people can't) UV is not visible.
(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))))))) (. .)))