what light does to leafy plants
Light provides the energy plants need to make the food required for them to grow and flower. Plants are the only organisms able to use the energy from light to produce sugars, starches and other substances needed by them as well as by other living organisms.
Give a plant too much sun and it will look bleached, pale, or event burned; too few hours and it will have thin leaves and elongated shoots. Some plants require about a half day of light, while others need up to 18 hours of light each day; the latter include vegetables, which will get pale without sufficient light.