It throws light on what has been written (7,4)
I believe the answer is:
reading lamp
'it throws light on what has been written' is the definition.
The definition suggests a singular noun which matches the answer.
'it throws light on' is the wordplay.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'throws' becomes 'rading' (I can't explain this - if you can you should give a lot more credence to this answer).
'light' becomes 'lamp' (lamp is a kind of light).
'on' is an insertion indicator (as in clothing 'on' a person).
'rading'+'lamp'='radinglamp'
'e' placed into 'radinglamp' is 'READING-LAMP'.
Can you help me to learn more?
(Other definitions for reading lamp that I've seen before include "Pale and grim (anag) - source of illumination" , "An aid to lucubration" , "Light in library, perhaps" .)