Notice one in wild speech incandescent (7)
I believe the answer is:
radiant
'incandescent' is the definition.
(I've seen this before)
'notice one in wild speech' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'wild speech' becomes 'rant' (I've seen this in another clue).
'ad'+'i'='adi'
'adi' placed within 'rant' is 'RADIANT'.
(Other definitions for radiant that I've seen before include "Effulgent" , "Shining - happy" , "Straight line" , "Very conspicuous" , "Lit up" .)