A ‘right to light’ takes no account of sunlight, overshadowing or orientation.  It relates ONLY to view of the sky, and only to rooms served by a window (or glazed door) opening.  As such, concerns regarding loss of sunlight to windows, or to external for amenity areas such as gardens and patios, are not covered by right to light law.  You may have grounds for objecting on planning grounds, for loss of sunlight to windows and gardens, but, if Planning Permission has been granted, (or is not required), a ‘right to light’ will not help you with sunlight concerns.  Of course, having a legal right to light may ultimately help you if you can prove your view of the sky will be diminished to a certain level.