Bulb could be lit up (5)
I believe the answer is:
tulip
'bulb' is the definition.
(I've seen this before)
'could be lit up' is the wordplay.
'could be' indicates an anagram.
'lit'+'up'='litup'
'litup' anagrammed gives 'TULIP'.
(Other definitions for tulip that I've seen before include "Spring-blooming plant" , "Plant of the lily family with a single showy flower" , "(Dutch) bloom" , "Bulbous plant" , "Amsterdam bloom?" .)