HOW MUCH SUN IS CONSIDERED FULL SUN?

As a New York City garden designer I first take analysis of a site before designing. My recommendation as a garden designer is to first observe how the sun moves through your property during the course of a day. Take notes.   

Full sun is considered to be over 6 hours of unobstructed light each day.

Partial sun ranges between 3 and 6 hours, and shade is considered to be less than 3 hours of light each day. Typically, the sunniest areas will be the west and south sides of your home unless shaded by large trees or other buildings. The best way to determine sun levels for the area in question is to check it every hour on a sunny day.

One of my garden design tricks as a professional garden designer is to document the garden via photographs with my iphone at various times of the day.  Having a visual record can sometimes be an effective reference.