Behold too much during quick departure that's illuminated (8)
I believe the answer is:
floodlit
'illuminated' is the definition.
(floodlighting is a kind of illuminating)
'behold too much during quick departure' is the wordplay.
'behold' becomes 'lo' (archaic exclamation meaning 'look!').
'too much' becomes 'od' (abbreviation for overdose).
'during' means one lot of letters goes inside another.
'quick departure' becomes 'flit' (I can't justify this - if you can you should believe this answer much more).
'lo'+'od'='lood'
'lood' placed inside 'flit' is 'FLOODLIT'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for floodlit that I've seen before include "like some football matches" , "Brightly illuminated" , "Given strong illumination" , "was intensely illuminating" , "as late matches are played?" .)