Significantly, does it light up in a new way? (4)
I believe the answer is:
neon
'significantly does it light' is the definition.
I know that 'light' relates to this answer.
'up in a new way?' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'in' indicates putting letters inside.
'a new' becomes 'non' (I can't explain this - if you can you should believe this answer much more).
'way?' becomes 'e' (Compass direction - East).
'non' going around 'e' is 'noen'.
'noen' back-to-front is 'NEON'.
Can you help me to learn more?
(Other definitions for neon that I've seen before include "Element 10, used in lights" , "None (anag.)" , "illuminating agent" , "Atomic number 10" , "Small plant; colour" .)