Storefront light (4)
I believe the answer is:
neon
'storefront light' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for neon that I've seen before include "Sign gas" , "Element 10, used in lights" , "One of the six inert gases" , "Colourless, odourless rare gas" , "Type of lighting" .)