Sunlight is the light and energy that comes from the Sun. When this energy reaches the earth's surface, it is called insolation. What we experience as sunlight is actually solar radiation. It is the radiation and heat from the Sun in the form of electromagnetic waves.Without sunlight, there could be no life on Earth. Plants need sunlight for the process of photosynthesis. Solar radiation can be both good and bad for a person's health. When in the light, the human body uses the ultraviolet part of sunlight to make its own Vitamin D.