The sun, a torch, and a light bulb all emit energy in the form of particles called photons. The photons from the sun are a product of thermonuclear fusion. A torch uses a chemical reaction to burn. A light bulb converts electricity to photons. But a photon is a photon – and light is light – whether it comes from the sun or a flashlight.

Vastly more energy comes from the sun than from any artificial light. But the light from the sun is different from a street lamp another way: most artificial light doesn’t emit as much energy in the red and blue region of the light spectrum as sunlight does. In other words, different ratios of reds, yellows and blues all combine together to make up white sunlight.

Researchers can successfully grow plants using only artificial light in growth chambers. But sunlight is best for most plants. It’s generally more intense than artificial light, and it’s pretty equally distributed among the different wavelengths that earthly plants have evolved to like best.

And there’s another difference between lamps – even “grow lamps” – and sunlight. Grow lamps need energy to light up. Sunlight is unlimited and free.

Our thanks to:
John Frederick
Department of Geophysical Science
University of Chicago
Chicago, IL

Cheryl Mackowiak
USU Research Greenhouse Facility
Logan, UT