Green light and how it was transmitted (6)

I believe the answer is:

assent

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'green light' is the definition.
(I've seen this in another clue)

'was transmitted' is the wordplay.
'was' becomes 'as' (I can't explain this - if you can you should believe this answer much more).
'transmitted' becomes 'sent' (sending is a kind of transmitting).
'as'+'sent'='ASSENT'

'and how it' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for assent that I've seen before include "Nod" , "Okay" , "Expression of agreement" , "Give the thumbs-up" , "Agree and concur" .)

I've seen this clue in The Sunday Times.

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