50 per cent of diaries, a hit when put on screen (4-4)

'screen' is the definition.
(I have seen 'French screen' mean 'abat jour' so perhaps 'screen' could also mean 'abat jour')

'50 per cent of diaries a hit when put on' is the wordplay.
'50 per cent of' indicates taking half.
'diaries' becomes 'journals' ('journal' can be a synonym of 'diary').
'hit when' becomes 'bat' (batting is a kind of hitting. I am not sure about the 'when' bit.).
'put on' is a charade indicator (letters next to each other).
'journals' cut in half is 'jour'.
'a'+'bat'='abat'
'jour' put after 'abat' is 'ABAT-JOUR'.

Can you help me to learn more?