Solar radiation is radiant (electromagnetic) energy from the sun. It provides light and heat for the Earth and energy for photosynthesis. The three relevant bands, or ranges, along the solar radiation spectrum are ultraviolet, visible light (PAR), and infrared. PAR is the light wavelength range that is best fit for photosynthesis to occur. Photosynthesis is a process that requires light energy and optimally occurs in the 400 to 700 nanometer (nm) range.
Depending on which crop you are growing in your fields or greenhouse, you will be looking for different amounts of PAR. Knowing the PAR for your production space will help you determine whether open field production will work with your intended crop or not. Alternatively, knowing PAR will help you determine whether you require shade nets in your greenhouse, which percentage transparency, whether you need to add or remove chalk from your greenhouse.