What Does Photosynthentically Active Radiation (PAR) Mean?
Photosynthetically active radiation, abbreviated PAR, is that part of the visible spectrum of light that plants utilize to perform photosynthesis. It occurs at wavelengths between 400 and 700 nanometers (nm). Blue and violet light are at the lower end and red light is at the higher end. Plants utilize different wavelengths of light during different phases of their development. During the vegetative stage of development, cannabis utilizes light with PAR values generally in the 400-500 nm range. During the flowering phase, they need light with PAR values above 620 nm. Growers can measure the amount of PAR their lights are emitting with relatively inexpensive PAR meters.