Is less generous about sweetheart up in lights again?

'lights again?' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how they can define each other.

'is less generous about sweetheart up' is the wordplay.
'is less generous' becomes 'stingier' ('stingy' can be the opposite of 'generous' so perhaps 'stingier' is reasonable for 'less generous').
'about' is an insertion indicator.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'up' says the letters should be written backwards (in down clue: letters go upwards).
'stingier' placed around 'e' is 'setingier'.
'setingier' written backwards gives 'RE-IGNITES'.

'in' acts as a link.

Can you help me to learn more?