( They ( ( ( ( emit and ) reflect ) ( light energy ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP emit) (CC and) (VBP reflect) (NP (JJ light) (NN energy))) (. .)))
They emit and reflect light energy.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NNS electrons)) (VP (VB return) (PP (TO to) (NP (DT a) (JJR lower) (NN energy) (NN level)))))) (, ,) (NP (PRP they)) (VP (VBP emit) (NP (NP (DT the) (JJ excess) (NN energy)) (PP (IN in) (NP (NP (DT the) (NN form)) (PP (IN of) (NP (NN light))))))) (. .)))