Just like humans and animals, plants need energy to survive and thrive, and they make their food themselves via a process called photosynthesis, which occurs only in the presence of light. This process takes place in the plant's food-producing chloroplasts, which contain the pigment chlorophyll present in all green plants.
TL;DR (Too Long; Didn't Read)
Plants need light to photosynthesize, but it doesn't necessarily have to be sunlight. If the correct type of artificial light is used, photosynthesis can happen at night with lights that contain blue and red wavelengths.
The Photosynthetic Process
Plants take in water through their roots, carbon dioxide from the air and energy from sunlight, and a chemical process involving all three enables them to perform photosynthesis to make glucose and oxygen. Glucose travels around the plant as soluble sugars, forming cellulose for cell walls and proteins for growth and repair. Plants use oxygen during photosynthesis to release carbon dioxide into the air, which is known as respiration. In 1779 Dutch biologist and chemist Jan Ingenhousz furthered the work of earlier scientists by proving three things: plants need light to photosynthesize, only the green parts of the plant perform photosynthesis and the environmental benefits of respiration outweigh the damage.
Plants and Respiration
Plant respiration uses oxygen to produce energy and give off carbon dioxide as a waste product, which makes it the opposite of photosynthesis, which uses carbon dioxide and produces oxygen. Respiration is vital to the health of the planet, as humans, animals and all other respiring organisms need the process of plant photosynthesis and respiration to survive. Plants respire all the time, whether it is dark or light, because their cells need energy to stay alive. But they can only photosynthesize when they have light.
Photosynthesis at Night
Several elements may affect the rate of photosynthesis: carbon dioxide concentration, temperature and light intensity. If there is insufficient carbon dioxide, a plant cannot photosynthesize, even if it has plenty of light. If it is too cold, the rate of photosynthesis will drop. If it is too hot, plants will not be able to photosynthesize.
If a plant doesn't have enough light, it cannot photosynthesize very quickly, even if it has sufficient water and carbon dioxide. How efficient an artificial light is to allow a plant to photosynthesize at night depends on its wavelengths.
Some artificial light sources consist of a lot of wavelengths not useful to plants, like green and yellow, meaning a lot of light is wasted. These light sources can still promote photosynthesis, but light that contains more red and blue wavelengths is more efficient because those wavelengths are the main ones used by plants.
About the Author
Claire is a writer and editor with 18 years' experience. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc.