If I trim 4 foot from the height of a hedge will this give me 4 foot more
light on my allotment?

The problem is, that during the day the sun travels the length of a hedge
that runs all the way up the side of the allotment and the hedge puts 50% of
the allotments's entire length in the shade. This is now - september. How
much will it decrease in winter and how much will it increase in summer?

My main question though, is does the amount you cut off equal the amount of
sunlight you gain.

Hope you can help, I think I've made a mistake with my choice of allotment
:-(