Plants usually come labelled with their sun exposure requirements. Measuring sun exposure for plants is not an exact science. There will always be variables such as cloudy days and places where it gets to be 100 degrees in the shade. The following descriptions are a good place to start.
FULL SUN: At least 6 full hours of direct sunlight. Many sun loving plants enjoy more then 6 hours per day but do need regular watering to endure the heat.
PARTIAL SUN/PARTIAL SHADE: These two terms are often used interchangeably to mean 3 to 6 hours of sun each day preferably in the morning and early afternoon. If a plant is listed as partial sun greater emphasis is on receiving the minimal sun requirements each day. If listed as partial shade the plant will need some relief from the intense late afternoon sun.
FULL SHADE: Less then 3 hours of direct sunlight each day with filtered sunlight the rest of the day. Full shade does not mean no sun. There aren’t many plants, except mushrooms, that can survive in the dark.