Left it switched on? (3)

I believe the answer is:

lit

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'switched on?' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe they are linked in a way I don't understand?

'left it' is the wordplay.
'left' becomes 'l' (common abbreviation).
'l'+'it'='LIT'

Can you help me to learn more?

(Other definitions for lit that I've seen before include "Enlightened" , "Creative writing, in short" , "was illuminating" , "Set alight" , "Fired" .)

I've seen this clue in the Evening Standard.

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