The sun, a torch, and a light bulb all emit energy in the form of particles called photons by scientists. The photons from the sun are a product of thermonuclear fusion, the torch uses a chemical reaction to burn, and the light bulb converts electricity to photons. Artificial light doesn't have the same spectral qualities as sunlight. In other words, it has different ratios of reds, yellows, and blues all combining together to make up white light. Artificial light doesn't emit as much energy in the red and blue region of the light spectrum as sunlight does.
Researchers can successfully grow plants using only artificial light in growth chambers.
Dafina, thanks for your question. With thanks to the National Science Foundation, we're Block and Byrd for Earth and Sky.