Easy to cry on retirement — this should brighten things up (5,4)
I believe the answer is:
light bulb
'this should brighten things up' is the definition.
(I've seen this before)
'easy to cry on retirement' is the wordplay.
'easy' becomes 'light' (similar in meaning).
'to cry' becomes 'blub' (I've seen this before).
'on retirement' is a reversal indicator.
'blub' back-to-front is 'bulb'.
'light'+'bulb'='LIGHT-BULB'
(Other definitions for light bulb that I've seen before include "should brighten things up" , "may be subject to changing" , "glower" , "Source of illumination" , "One should make things clear" .)