Thought i'd point you to a webpage of a company that have just redone
my kitchen. Look for the 'How Much Light?' bit of this page - it lists
a formula you can use to roughly calculate the amoutn of light needed.
As with anything, if you want a dead-on answer, probably best to email
them and ask. They were really friendly and helpful with me.
Here's the page :-
and their kitchen range.
Hope this helped!