Editor's note: This article has been reviewed and updated for accuracy in 2026. Lighting is one of, if not the most essential ingredient needed for a quick, high-yielding crop. Your lights may very well be your single greatest expense, but very well worth the investment. Maximizing light distribution to your plants will enhance photosynthesis tremendously. Photosynthesis is the process by which carbon dioxide and water are turned into sugary plant food and oxygen. This works the same for your common houseplant as it does for your favorite strain of sticky icky. Regardless of plant type, the effect is similar; the more light your plants receive, the faster and bigger they will grow. Understanding How Grow Lights Work Light is made of photons, which are tiny particles that inexorably travel at the speed of light. Photons in light beams vibrate with different frequencies and wavelengths. Humans can see photonic radiations within wavelengths from 380–680nm, while plants’ sensitivity to light ranges from 200–800nm. Not all wavelengths within this spectrum produce the same effects on photosynthesis; those that most activate biochemical processes in plants are called PAR (photosynthetically active radiation), which has a spectral range of 400–700nm. Light can be measured in photometric quantities derived from the human eye’s sensitivity to color, or else with radiometric quantities related to the energy transported by light beams. Lumens and lux are commonly used photometric units that refer to light perceived by the human eye. However, photometric measurements do not indicate how much light energy a lamp sends to a plant for photosynthesis because they don’t include the PAR variables.