Just looked at the plans and I can't see that it will have any (or any significant) effect on light - it's an "in-fill" extension of the side return of the house as I understand it - so the extension does not go beyond the line of the rear of the property - when it talks about extending approx 6m from the rear of the original property it means from the dining room window - not 6m from the kitchen (at least that's how I read the plans).