PAR value is the photosynthetic photon flux, measured in micromoles (μmoles) per meter squared per second.
If that sounds confusing, don’t fret as we will try to simplify this metric.
Photosynthesis is the process by which plants use sunlight (or indoor grow lighting) to synthesize foods from carbon dioxide and water and give off oxygen as a by-product, resulting in plant growth. The number of photons of light determines the photosynthetic photon flux mentioned above.
Natural sunlight has a PAR value of 1200-1400 micromoles (μmoles). An effective grow light will have a PAR value between 800-1400μmoles. Using lighting with higher PAR values may be counterproductive and cause stunted growth of plants.