One cycling with new type of light (4)
I believe the answer is:
neon
'type of light' is the definition.
(I've seen this in another clue)
'one cycling with new' is the wordplay.
'cycling with' indicates an anagram.
'new' becomes 'n' (abbreviation as in New Testament NT).
'one' anagrammed with 'n' gives 'NEON'.
(Other definitions for neon that I've seen before include "Element that gives a red glow in a vacuum tube" , "Type of lighting" , "None (anag.)" , "One of the six inert gases" , "Gas used in fluorescent lamps" .)