If the sun stops giving light following things will occur:
Photosynthesis is the process through which plants make food, and it is only possible when sunlight is available as a source of energy.
Photosynthesis emits considerable oxygen into the air; the atmosphere contains very little oxygen.
Many plants rely on light to fulfill their photoperiodic flowering requirements.
Many animals rely on light to time their feeding, reproductive, and migratory behaviors, and they employ daily and seasonal variations in light intensity and duration (photoperiod).