Photosynthetically active radiation

The expression Photosynthetically Active Radiation, often abbreviated PAR, designates the spectral range of solar ozone layer in the stratosphere. Photons at longer wavelengths do not carry enough energy to allow photosynthesis to take place, and plants have developed, through billions of years of evolution, the capacity to scatter these photons away, hence the very high reflectance and transmittance of live green leaves.