Bright light in the big city (4)
I believe the answer is:
neon
'bright light in the big city' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neon that I've seen before include "Noble gas used in illuminated signs" , "Colourless, odourless rare gas" , "None (anag.)" , "It may illuminate" , "Gas - light" .)