Lighter and firm dip at the end of the day? (6)
I believe the answer is:
sunset
'dip at the end of the day?' is the definition.
'lighter and firm' is the wordplay.
'lighter' becomes 'sun' (something which lights).
'and' is a charade indicator (letters next to each other).
'firm' becomes 'set' (I've seen this before).
'sun'+'set'='SUNSET'
(Other definitions for sunset that I've seen before include "brilliant decline?" , "The fading light of evening" , "Evening glow" , "End of the day, getting dark" , "Final declining phase (of something)" .)