Most plants come with their sun exposure requirements on the lable but what does the terminology actually mean. Measuring plant sun exposure is not exact. There are always cloudy days and sometimes a particular spot in the shade will get really hot.
Plants graded as needing full sun conditions will require at least six hours of direct sunlight a day. The term that describe these plants is Heliophilous-helio for 'sun' and philous for 'like'. Generally a south facing wall will receive the most sun which is where these plants should be grown. Plants graded as requiring full sun need the energy from the sun to be at their best. They can be grown without full sun conditions but they will not do as well. These plants need all the energy that is available to produce their flowers,fruit or vegetables.