Crops require light in order to carry out photosynthesis, produce carbohydrates, and increase biomass (grow!). Plants absorb light through their leaves, and therefore the more or bigger leaves in their canopy the more light they can absorb. As the amount of light absorbed by a plant increases, the photosynthetic rate also increases to a certain point as long as other nutrients are not limited. Heat as the result of light or photosynthesis is released from the plant through transpiration.

Too much light, either in length or power, can have negative effects on plant health. Plants can experience sun damage in the form of chlorosis- a yellowing of the leaf surface where the chlorophyll is lost. Chlorosis is not only caused by too much light, but can also be a sign of nutrient deficiencies and some diseases. Another way plants can protect themselves from too much light is the buildup of anthocyanins- deep purple or red molecules that act as a physical barrier to light.

Since plants require light to grow, if a light source is placed on one side of a plant, then that plant may grow in the direction of the light. This phenomenon is called phototropism.

Light can be supplied by natural sunlight or by artificial light sources.