Bulb illuminated, one working (5)

I believe the answer is:

onion

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'bulb' is the definition.
(onion is a kind of bulb)

'illuminated one working' is the wordplay.
'illuminated' becomes 'oni' (I can't explain this - if you can you should give a lot more credence to this answer).
'one working' becomes 'on' (on can mean working or activated).
'oni'+'on'='ONION'

Can you help me to learn more?

(Other definitions for onion that I've seen before include "Type of allium" , "Bulb used in cooking" , "it can bring tears" , "Tear-jerking bulb" , "Strong tasting vegetable" .)

I've seen this clue in The Telegraph.

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