( ( Some ( of ( ( Chappelle 's ) ( ( most interesting ) work ) ) ) ) ( ( was ( in ( ( the area ) ( of ( ( luminescence , ) ( which ( is ( light ( without heat ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT Some)) (PP (IN of) (NP (NP (NNP Chappelle) (POS 's)) (ADJP (RBS most) (JJ interesting)) (NN work)))) (VP (VBD was) (PP (IN in) (NP (NP (DT the) (NN area)) (PP (IN of) (NP (NP (NN luminescence)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (ADJP (JJ light) (PP (IN without) (NP (NN heat)))))))))))) (. .)))
Some of Chappelle's most interesting work was in the area of luminescence, which is light without heat.
(ROOT (S (NP (NP (NNP Producing) (NN light)) (PP (IN without) (NP (NN heat)))) (VP (VBZ is) (VP (VBN called) (S (ADJP (JJ luminescence))))) (. .)))